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Tetrahedron 68 (2012) 3172e3178

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Tetrahedron

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A N-heterocyclic carbene (NHC) platinum complex as pre-catalyst for theintramolecular hydroamination of olefins with secondary alkylamines andoxidative amination of u-alkenic amines

Rui Zhang a, Qin Xu a,*, Liang-yong Mei a, Sheng-ke Li a, Min Shi a,b,*aKey Laboratory for Advanced Materials and Institute of Fine Chemicals, School of Chemistry & Molecular Engineering, East China University of Science and Technology,130 Mei-Long Road, Shanghai 200237, Chinab State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, China

a r t i c l e i n f o

Article history:Received 17 January 2012Received in revised form 21 February 2012Accepted 22 February 2012Available online 1 March 2012

Keywords:N-Heterocyclic carbenePlatinum complexIntramolecular hydroamination

* Corresponding authors. Fax: þ86 21 64166128;sioc.ac.cn (M. Shi).

0040-4020/$ e see front matter � 2012 Elsevier Ltd.doi:10.1016/j.tet.2012.02.060

a b s t r a c t

A N-heterocyclic carbene (NHC) platinum complex 3 prepared from BINAM was found to be a highlyeffective pre-catalyst for the intramolecular hydroamination of olefins with secondary alkylamines togive the corresponding intramolecular hydroamination products in excellent yields. The substrate scopehas been carefully examined and the plausible reaction mechanism has been also proposed.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Metal-catalyzed intramolecular hydroamination of unactivatedalkenes is one of the simplest and most atom-economical ap-proaches to the construction of nitrogen containing heterocycles.1

Although the synthetic potential of cyclohydroamination is signif-icant, the development of a catalytic system applicable to the ad-dition of primary or secondary amines to olefins remains aninteresting challenge. Various catalysts that involve differentmetals have been developed.2 For example, a variety of catalysts,based on rare earth elements and actinides,1i,3 alkali and alkalineearth metals,4 group 4 metals,5 are known to catalyze the hydro-amination with superb efficiency. Recently, a variety of late tran-sition metal complexes based on Pt,6 Rh in which anenantioselective hydroamination of unactivated alkenes withamines has been also presented,7 Pd,8 Ir,9 Cu,10 and Au6c,11 havebeen reported as catalysts for the intramolecular hydroamination.However, there still remains room for further investigation on thereaction efficiency.

N-heterocyclic carbenes (NHCs) ligands are stronger s-donorand weaker p-acceptor than phosphine ligands,12 and some metal

e-mail address: mshi@mail.-

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complexes derived fromNHCs ligands are often air/moisture stable,which makes handling much more convenient.13 Previously, ourresearch group has synthesized a novel class of cis-chelatedbidentate bis(NHC)-Rh, Pd and Ir complexes from 1,10-binaph-thalenyl-2,20-diamine (BINAM) and H8-BINAM, and successfullyapplied them in several catalytic reactions.14 In this paper, we wishto report the synthesis and application of a novel NHCePt(II)complex derived from BINAM in the intramolecular hydro-amination of olefins with secondary alkylamines under mildconditions.

2. Results and discussion

2.1. Synthesis of NHCePt(II) complex 3

As shown in Scheme 1, the NHCePt complex 3 was synthesizedin a three-step pathway starting from 2,20-di(1H-benzoimidazol-1-yl)-1,10-binaphthyl 1 (see Supplementary data for the details).Namely, the reaction of compound 1 with iodomethane in aceto-nitrile under reflux afforded the corresponding imidazolium salt 2in good yield, which could be smoothly transformed to the corre-sponding NHCePt(II) complex 3 upon treatingwith Pt(COD)Cl2. Thecrystal structure of complex 3 has been determined by X-ray dif-fraction. Its ORTEP drawing is shown in Fig. 115 and the related CIFdata are presented in the Supplementary data.

Scheme 1. Synthesis of NHCePt(II) complex 3.

Fig. 1. ORTEP drawing of NHCePt(II) complex 3 with thermal ellipsoids at the 30%probability level. Selected bond distances (�A) and angles (deg): PteC(1)¼1.978(14),PteI(1)¼2.6657(11), PteC(9)¼1.978(15), PteI(2)¼2.6679(11), C(9)ePteI(1)¼86.4(4),C(1)ePteI(2)¼87.7(5), N(1)eC(1)eN(2)¼108.2(12), N(3)eC(9)eN(4)¼107.2(12).

Table 1Optimization of reaction conditionsa

NHBn

Ph

PhNHC-Pt complex 3 (3 mol %)additive, solvent, temp

NPhPh

Bn

Me

4a 5a

Entry Solvent Additive Temp (�C) Yieldb (%)

1 1,4-Dioxane / 90 n.r.d

2c Benzene AgBF4 80 n.r.d

3 1,4-Dioxane AgBF4 90 404 Toluene AgBF4 90 835 Benzene AgBF4 80 >996 THF AgBF4 65 147 Cl2CHCHCl2 AgBF4 90 478 DCE AgBF4 80 849 AgBF4DMF AgBF4 90 1110 Chlorobenzene AgBF4 90 2511 CH3CN AgBF4 80 6312 Benzene AgBF4 20 n.r.d

13 Benzene AgBF4 60 4014 Benzene AgBF4 120f 2515 Benzene AgOAc 80 2016 Benzene AgOTf 80 8017 Benzene AgOTs 80 8218 Benzene AgSbF6 80 9019 Benzene AgOCOCF3 80 7020e Benzene AgBF4 80 45

a Reaction conditions: substrate 4a (0.25 mmol), NHCePt(II) complex 3 (3 mol %),solvent (1.0 mL), and additive (0.015 mmol, 6 mol %) for 48 h.

b Isolated yields.c Reaction conditions: substrate 4a (0.25 mmol), solvent (1.0 mL), and AgBF4

(0.015 mmol, 6 mol %) without NHCePt(II) complex 3 for 48 h.d No reaction.e Reaction conditions: substrate 4a (0.25 mmol), NHCePt(II) complex 3 (3 mol %),

solvent (1.0 mL), and additive (0.015 mmol, 6 mol %) for 24 h.f Oil-bath temperature.

R. Zhang et al. / Tetrahedron 68 (2012) 3172e3178 3173

2.2. NHCePt(II) complex 3 along with AgBF4 catalyzedintramolecular hydroamination

Initial examinations using 4a as substrate in the presence ofNHCePt(II) complex 3 (3 mol %) in 1,4-dioxane were aimed at de-termining the optimal conditions and the results of these

experiments are summarized in Table 1. It was found that no re-action occurred only in the presence of NHCePt complex 3 evenwhen the reactionwas carried out at 90 �C (oil-bath) as well as onlyin the presence of AgBF4 (Table 1, entries 1e2). However, the de-sired product 5a was obtained in 40% yield in the presence ofNHCePt pre-catalyst 3 (3 mol %) along with AgBF4 (6 mol %) in 1,4-dioxane for 48 h (Table 1, entry 3). The examination of solvent

Table 2Intramolecular hydroamination of unactivated alkenes in the presence of per-catalyst 3 along with AgBF4a

Entry Alkenyl amine Product Yieldb (%)

1 n¼1, R¼4-BrC6H4 5b 932 n¼1, R¼4-CNC6H4 5c 953 n¼1, R¼4-NO2C6H4 5d 944 n¼1, R¼4-CO2MeC6H4 5e 925 n¼1, R¼4-MeC6H4 5f 906 n¼1, R¼4-OMeC6H4 5g 857 n¼1, R¼Cy 5h 92

8 n¼1, R¼Ph 5i 95

9 n¼1 5j 8510 n¼2 5k 90

11 85

12 90

13 n.r.c

14 n¼1 5o 88

15 n¼2 5p 90

16 n¼1 5q 90 (1.8:1)17 n¼2 5r 92 (1.4:1)

18 90

19 95

a Reaction conditions: substrate (0.25 mmol), NHCePt(II) complex 3 (3 mol %),benzene (1.0 mL), and additives (0.015 mmol, 6 mol %) at 80 �C for 48 h.

b Isolated yields.c No reaction.

R. Zhang et al. / Tetrahedron 68 (2012) 3172e31783174

effects revealed that benzene was the best solvent, affording 5a in>99% yield under identical conditions (Table 1, entries 4e11).Lowering the reaction temperature to 60 �C produced 5a in 40%yield and no reaction occurred at 20 �C (Table 1, entries 12 and 13).Elevating the reaction temperature to 120 �C (oil-bath) dramati-cally decreased the yield of 5a (Table 1, entry 14). Moreover, varioussilver salts have been examined in this reaction as the additives andwe found that AgBF4 was the best choice for the intramolecularhydroamination (Table 1, entries 5 and 15e19). Shortening the re-action time to 24 h afforded 5a in 45% yield (Table 1, entry 20).

Having identified the optimal reaction conditions, substratescope of this intramolecular hydroamination has been evaluatedusing a variety of amino olefins. The results are summarized inTable 2. The presence of bromo, cyano, nitro, ester, methyl, ormethoxy substituents within the benzylamines did not signifi-cantly influence the reaction outcomes (Table 2, entries 1e6) andthe aliphatic N-methylcyclohexyl aminoalkene also provided thecorresponding product in good yield (Table 2, entry 7). gem-Dialkylor diphenyl substitution at the b-position of these g-amino olefinswas not essential, but it could facilitate this intramolecular hydro-amination to give the cyclized products in higher yields (Table 1,entry 5 and Table 2, entries 9, 11, 12, and 14). The hexenylaminesubstrates also underwent the cyclization efficiently under theoptimal conditions, affording the corresponding piperidine andmorpholine derivatives in good yields (Table 2, entries 8, 10, 12, 15,and 17). Amide substrate bearing electron-withdrawing N-sub-stituent, such as Ts group also underwent hydroaminationsmoothly in high yield (Table 2, entry 18), although using stericallybulky N-Boc group protected amide as substrate, no reaction oc-curred (Table 2, entry 13). As can be seen from entry 19 in Table 2,this NHCePt complex along with AgBF4 also tolerate the alkenylterminal substituted aminoalkene, giving the correspondingproduct 5t in 95% yield. All of the products were obtained as ra-cemates and using axially chiral NHCePt(II) complex 3 as the pre-catalyst with AgBF4 gave the product 5 in 3% ee.

Furthermore, this NHCePt complex along with AgBF4 catalyticsystem was also effective in the intramolecular hydroamination ofu-alkenic amine 6d to give the corresponding indole derivative 7din moderate yield in the presence of 3mol % of NHCePt pre-catalyst3 and AgBF4 (6 mol %) under air at 80 �C (oil-bath, 90 �C) in benzene(Scheme 2) (see Table SI-1 in the Supplementary data).

It should be also noted that NHCePd(II) complex 8 (Fig. 2),which was also prepared from compound 2 according to our pre-vious literature14a is totally ineffective in above intramolecularhydroamination of unactivated alkenes, although it is moderatelyeffective in the oxidative amination (see Table SI-1 in theSupplementary data).

On the basis of above investigation and previous mechanisticstudies by Widenhoefer,6a Stahl,16 and Hartwig,9b a plausible cata-lytic cycle is outlined in Scheme 3. The reaction of NHCePt(II) com-plex with 4a gives NHCePt complex I via ligand exchange. Theintramolecular nucleophilic attack of nitrogen atom to the olefin ofcomplex I affords zwitterionic Pt complex II, which rapidly reactswith amine (NR3) existed in reaction system to form complex IValong with the release of species III (HBF4$NR3). Subsequently, thecorresponding Pt(IV) complex V is formed via oxidative additionbetween species III and complex IV along with the regeneration ofNR3.Next, the reductive elimination takesplace to afford theNHCePtcomplex VI, which produces the desired product 5a via ligand ex-change with 4a along with the formation of Pt-amine complex VII.Then, the NHCePt complex I can be regenerated from species VII.

3. Conclusion

In summary, the NHCePt(II) complex along with AgBF4 catalyticsystem is highly efficient in the intramolecular hydroamination of

Scheme 2. NHCePt(II) complex 3 along with AgBF4 catalyzed oxidative amination of u-alkenic amine to produce indole.

Fig. 2. NHCePd(II) complex 8.

NPhPh Me

Bn

II

N

PhPh

Bn HPtL2BF4

NPhPh

Bn PtL2

N

PhPh

(H)L2BF4PtBn

NPhPh

Bn

MePtL2BF4

PhPh

NBn

PtL2

BF4

PhPh

NHBn

PtL2BF4

I

IV

V

VII

4a

5a H

VI

PhPh NHBn

[HNR3]BF4[HNR3]BF4NR3III

NR3

III

Scheme 3. A plausible mechanism for the catalytic intramolecular hydroamination.

R. Zhang et al. / Tetrahedron 68 (2012) 3172e3178 3175

olefins in benzene at 80 �C for a variety of amino olefins, giving pyr-rolidine and piperidine derivatives in excellent yields. Further studiesto find more efficient catalysts based on NHC ligands and to furtherelucidate the mechanistic details of this reaction are underway.

4. Experimental section

4.1. General remarks

All reactions and manipulations were performed using stan-dard Schlenk techniques. Melting points were measured ona Yanagimoto micro melting apparatus and uncorrected. NMRspectra were recorded with a Varian Mercury vx or Brukerspectrometer at 300 MHz or 400 MHz (1H NMR), 75 MHz or

100 MHz (13C NMR) in CDCl3, respectively. Chemical shifts werereported in parts per million down field from internal TMS.Optical rotations were determined at 589 nm (sodium D line)using a PerkineElmer 341 MC Polarimeter. [a]D values are givenwith units of 10 cm2 deg�1 g�1. Mass spectra were recorded onthe HP-5989 instrument by EI/ESI methods. Infrared spectrawere recorded on a PerkineElmer PE-983 spectrometer withabsorption in cm�1. Satisfactory CHN microanalyses were ob-tained by using a Carlo-Erba 1106 analyzer X-ray diffractionanalysis was performed by using a Bruker Smart-1000 X-raydiffractometer. Chiral HPLC was performed by using a SHIMADZU

SPD-10A vp series instrument with chiral columns (Chiralpak OJ-H, OD-H, and AD-H columns, ɸ 4.6�250 mm, Daicel Chemical Co.Ltd). Organic solvents used were dried by standard methodswhen necessary. Commercially obtained reagents were usedwithout further purification. All reactions were monitored by TLCwith Huanghai GF254 silica gel coated plates. Flash columnchromatography was carried out using by using 300e400 meshsilica gel at increased pressure.

4.2. General procedure for the synthesis of N-heterocycliccarbene Pt(II) complexe 3

2,20-di (1H-benzo[d]imidazol-1-yl)-1,10-binaphthyl 1. This isa known compound.14d White solid; mp 294.5e294.8 �C. 1H NMR

R. Zhang et al. / Tetrahedron 68 (2012) 3172e31783176

(400 MHz, CDCl3, TMS): d 8.06 (d, J¼8.8 Hz, 4H), 7.67e7.63 (m, 2H),7.55e7.48 (m, 6H), 7.43 (d, J¼8.8 Hz, 2H), 6.99 (s, 2H), 6.95 (d,J¼8.0 Hz, 2H), 6.50 (t, J¼7.6 Hz, 2H), 6.11 (d, J¼8.0 Hz, 2H).

4.3. The procedure for the synthesis of the imidazolium salt 2

Compound 1 (485 mg, 0.4 mmol) and MeI (8.0 mmol, 20 equiv)in MeCN (10 mL) were stirred under reflux for 12 h. After cooling toroom temperature, volatiles were removed under reduced pressureand the obtained solid compound 2 was used for the next reactionwithout any further purification.

Imidazolium salt 2. This is a known compound.14d A yellow solid.1H NMR (400MHz, CDCl3, TMS): d 10.20 (s, 2H), 8.28e7.34 (m, 20H),3.95 (s, 6H).

4.4. General procedure for the synthesis of the NHCePt(II)complex 3

Compound 2 (0.2 mmol), Pt(COD)Cl2 (96.5 mg, 0.2 mmol),NaOAc (0.2 mmol), KI (0.4 mmol) was added to a dry flask underargon, and then refluxed in MeCN (10 mL) for 48 h. The volatileswere removed under reduced pressure and the residue waspurified by a silica gel flash column chromatography (eluent:petroleum ether/EtOAc, 2/1 to 0/1) to give 3 as a yellow solid in77% yield.

NHCePt(II) complex 3. A yellow solid, mp >300 �C (dec); IR(CH2Cl2) n 3056, 2965, 2881, 2083, 1777, 1862, 1586, 1511, 1495,1479, 1433, 1374, 1337, 1301, 1263, 1223, 1091, 1025, 970, 870, 806,764, 747, 698, 673 cm�1. 1H NMR (400MHz, CDCl3, TMS): d 8.07 (dd,J¼12.8, 10.8 Hz, 4H), 7.71 (d, J¼8.4 Hz, 2H), 7.23 (dt, J¼0.4, 8.0 Hz,2H), 6.93e6.89 (m, 4H), 6.83 (dt, J¼0.8, 8.0 Hz, 2H), 6.75e6.71 (m,4H), 6.66 (d, J¼8.0 Hz, 2H), 3.72 (s, 6H) (we did not use CH2Cl2 as thesolvent during the purification). MS (ESI)m/z: 877.1 (Mþ�IþCH3CN,100). HRMS (ESI) calcd for C38H29IN5Pt requires: 877.1115. Found:877.1110. Anal. Calcd for C36H26I2N4Pt$CH2Cl2: C: 42.39%, H: 2.69%,N: 5.34%, found: C: 42.50%, H: 2.88%, N: 5.30%. Crystals that weresuitable for X-ray diffraction analysis were grown from solutions inCH2Cl2/hexane (2:1).

4.5. General procedure for the synthesis of N-heterocycliccarbene Pd(II) complex 8

Compound 2 (0.2 mmol) and Pd(OAc)2 (44.8 mg, 0.2 mmol) wasrefluxed in THF (10 mL) for 30 h. The volatiles were then removedunder reduced pressure and the residue was purified by a silica gelflash column chromatography (eluent: petroleum ether/EtOAc, 2/1to 0/1) to give 8 as a yellow solid in 65% yield.

NHCePd(II) complex 8. This is a known compound,14d a brownsolid; mp >300 �C (dec). 1H NMR (300 MHz, CDCl3, TMS):d 8.10e8.03 (m, 4H), 7.72 (d, J¼8.4 Hz, 2H), 7.25e7.19 (m, 2H),6.94e6.87 (m, 4H), 6.85e6.82 (m, 2H), 6.78e6.74 (m, 4H), 6.68 (d,J¼8.7 Hz, 2H), 3.82 (s, 6H).

4.6. General procedure for NHCePt(II) complex and AgBF4catalyzed intramolecular hydroamination of olefins withsecondary alkylamines

The NHCePt(II) pre-catalyst 3 (3 mol %, 7.5 mmol) were dissolvedin solvent (1.0 mL) in a flame-dried Schlenk tube equipped witha septum cap and stirring bar. The additive (15.0 mmol) was addedunder argon, and then the mixture was stirred under argon at roomtemperature for 10 min. Then the alkylamine (0.25 mmol) wasadded, and the reaction mixture was stirred at 80 �C (oil-bath,90 �C) for 48 h. After that, the saturated aqueous solution of H2O(5 mL) was added. The organic phase was separated and theresulting aqueous layer was extracted with EtOAc. The combined

organic phases were filtered through a thin-layer of Celite. Thefiltrate was washed with brine (5 mL), dried over anhydrousNa2SO4, concentrated under reduced pressure, and purified by flashchromatography on silica gel (eluent: EtOAc/petroleum ether¼1/16) to yield the pure corresponding product.

4.6.1. 1-Benzyl-2-methyl-4,4-diphenylpyrrolidine (Table 1, entry 5,5a). A known compound,6a 99% yield, white solid. 1H NMR(400 MHz, CDCl3, TMS): d 7.37e7.29 (m, 4H), 7.28e7.07 (m, 11H),4.08 (d, J¼13.6 Hz, 1H), 3.63 (d, J¼10.0 Hz, 1H), 3.24 (d, J¼13.2 Hz,1H), 2.91 (dd, J¼7.6, 12.8 Hz, 1H), 2.85e2.76 (m, 2H), 2.20 (dd, J¼7.6,12.4 Hz, 1H), 1.16 (d, J¼5.6 Hz, 3H). 13C NMR (100MHz, CDCl3, TMS):d 150.6, 148.7, 140.1, 128.6, 128.2, 128.1, 127.8, 127.4, 127.2, 126.8,125.8, 125.4, 66.4, 59.6, 58.0, 52.5, 48.0, 19.5.

4.6.2. 1-(4-Bromobenzyl)-2-methyl-4,4-diphenylpyrrolidine (Table 2,entry 1, 5b). A known compound,6a 93% yield, white solid. 1H NMR(400 MHz, CDCl3, TMS): d 7.43 (d, J¼8.4 Hz, 2H), 7.27e7.20 (m, 8H),7.18e7.09 (m, 4H), 3.99 (d, J¼13.6 Hz, 1H), 3.59 (d, J¼9.6 Hz, 1H),3.21 (d, J¼13.6 Hz, 1H), 2.91 (dd, J¼8.0, 12.8 Hz, 1H), 2.85e2.80 (m,1H), 2.76 (d, J¼9.6 Hz, 1H), 2.21 (dd, J¼7.6, 12.4 Hz, 1H), 1.15 (d,J¼6.4 Hz, 3H). 13C NMR (100MHz, CDCl3, TMS): d 150.4,148.5, 139.2,131.3, 130.2, 128.2, 127.8, 127.3, 127.1, 125.8, 125.5, 120.5, 66.3, 59.6,57.3, 52.5, 47.8, 19.4.

4.6.3. 4-((2-Methyl-4,4-diphenylpyrrolidin-1-yl)methyl)benzonitrile(Table 2, entry 2, 5c). A known compound,6a 95% yield, pale yellowsolid. 1H NMR (400 MHz, CDCl3, TMS): d 7.60 (d, J¼8.4 Hz, 2H), 7.46(d, J¼7.6 Hz, 2H), 7.29e7.21 (m, 2H), 7.19e7.12 (m, 8H), 4.08 (d,J¼14.0 Hz, 1H), 3.59 (d, J¼9.2 Hz, 1H), 3.36 (d, J¼14.0 Hz, 1H),2.94e2.82 (m, 3H), 2.30e2.22 (m, 1H), 1.16 (d, J¼5.6 Hz, 3H). 13CNMR (100 MHz, CDCl3, TMS): d 150.0, 148.3, 145.9, 132.1, 129.0,128.2, 127.9, 127.3, 127.0, 126.0, 125.6, 119.0, 110.7, 66.4, 59.7, 57.6,52.7, 47.6, 19.4.

4.6.4. 2-Methyl-1-(4-nitrobenzyl)-4,4-diphenylpyrrolidine (Table 2,entry 3, 5d). A known compound,6a 94% yield, yellow solid. 1HNMR (400 MHz, CDCl3, TMS): d 8.09 (d, J¼8.8 Hz, 2H), 7.43 (d,J¼8.4 Hz, 2H), 7.21e7.04 (m, 10H), 4.03 (d, J¼14.0 Hz, 1H), 3.51 (d,J¼10.0 Hz, 1H), 3.33 (d, J¼14.4 Hz, 2H), 2.87e2.80 (m, 2H), 2.76(d, J¼10.0 Hz, 1H), 2.23e2.16 (m, 1H), 1.10 (d, J¼5.6 Hz, 3H). 13CNMR (100 MHz, CDCl3, TMS): d 150.0, 148.3, 148.2, 147.0, 129.0,128.2, 127.9, 127.3, 127.0, 125.9, 125.6, 123.5, 66.4, 59.7, 57.3, 52.7,47.6, 19.4.

4.6.5. Methyl-4-((2-methyl-4,4-diphenylpyrrolidin-1-yl)methyl)ben-zoate (Table 2, entry 4, 5e). A known compound,6a 92% yield,yellow oil. 1H NMR (400 MHz, CDCl3, TMS): d 7.99 (d, J¼8.4 Hz,2H), 7.43 (d, J¼8.4 Hz, 2H), 7.27e7.20 (m, 6H), 7.19e7.09 (m, 4H),4.09 (d, J¼14.0 Hz, 1H), 3.91 (s, 3H), 3.60 (d, J¼10.0 Hz, 1H), 3.32(d, J¼14.0 Hz, 1H), 2.94e2.82 (m, 2H), 2.78 (d, J¼10.0 Hz, 1H),2.23 (dd, J¼7.6, 12.8 Hz, 1H), 1.16 (d, J¼6.4 Hz, 3H). 13C NMR(100 MHz, CDCl3, TMS): d 167.1, 150.3, 148.5, 145.7, 129.6, 128.7,128.4, 128.2, 127.9, 127.3, 127.1, 125.9, 125.5, 66.4, 59.7, 57.7, 52.6,52.0, 47.8, 19.5.

4.6.6. 2-Methyl-1-(4-methylbenzyl)-4,4-diphenylpyrrolidine (Table2, entry 5, 5f). An unknown compound, 90% yield, colorless oil. IR(CH2Cl2) n 3084, 3056, 3024, 2965, 2796, 1684, 1599, 1514, 1493,1446,1374, 1262, 1097, 1031, 806, 760, 699 cm�1. 1H NMR (400MHz,CDCl3, TMS): d 7.27e7.08 (m, 14H), 4.04 (d, J¼13.2 Hz, 1H), 3.63 (d,J¼10.0 Hz, 1H), 3.21 (d, J¼13.2 Hz, 1H), 2.91 (dd, J¼7.6, 12.4 Hz, 1H),2.83e2.75 (m, 2H), 2.34 (s, 3H), 2.19 (dd, J¼7.6, 12.4 Hz, 1H), 1.16 (d,J¼6.0 Hz, 3H). 13C NMR (100MHz, CDCl3, TMS): d 150.7, 148.8, 136.9,136.3, 128.9, 128.6, 128.1, 127.8, 127.4, 127.3, 125.8, 125.4, 66.3, 59.6,57.7, 52.5, 48.0, 21.1, 19.5. MS (%) m/z 341.2 (Mþ, 23), 326.2 (80),

R. Zhang et al. / Tetrahedron 68 (2012) 3172e3178 3177

161.1 (100), 105.1 (74), 77.0 (6), 56.0 (79). HRMS (EI) calcd forC25H27N requires: 341.2143. Found: 341.2138.

4.6.7. 1-(4-Methoxybenzyl)-2-methyl-4,4-diphenylpyrrolidine (Table2, entry 6, 5g). A known compound,17 85% yield, colorless oil. 1HNMR (400 MHz, CDCl3, TMS): d 7.28e7.08 (m, 12H), 6.86 (d,J¼8.8 Hz, 2H), 4.01 (d, J¼12.4 Hz, 1H), 3.81 (s, 3H), 3.62 (d, J¼9.6 Hz,1H), 3.19 (d, J¼12.8 Hz, 1H), 2.91 (dd, J¼7.6, 12.4 Hz, 1H), 2.83e2.75(m, 2H), 2.19 (dd, J¼8.0, 12.8 Hz, 1H), 1.15 (d, J¼5.6 Hz, 3H). 13C NMR(100 MHz, CDCl3, TMS): d 158.5, 150.7, 148.7, 132.0, 129.7, 128.1,127.8, 127.4, 127.2, 125.8, 125.4, 113.6, 66.2, 59.6, 57.3, 55.2, 52.4,47.9, 19.4.

4.6.8. 1-(Cyclohexylmethyl)-2-methyl-4,4-diphenylpyrrolidine (Table2, entry 7, 5h). A known compound,17 92% yield, colorless oil. 1HNMR (400 MHz, CDCl3, TMS): d 7.30e7.27 (m, 4H), 7.24e7.10 (m,6H), 3.82 (d, J¼9.2 Hz, 1H), 2.85e2.76 (m, 2H), 2.63e2.58 (m, 1H),2.53e2.48 (m, 1H), 2.12e1.99 (m, 3H), 1.73e1.66 (m, 4H), 1.54e1.45(m,1H), 1.21e1.15 (m, 3H), 1.06 (d, J¼5.6 Hz, 3H), 0.96e0.88 (m, 2H).13C NMR (100 MHz, CDCl3, TMS): d 151.2, 148.8, 128.1, 127.8, 127.5,127.2, 125.8, 125.4, 67.6, 61.4, 60.3, 52.8, 48.0, 37.3, 32.2, 31.8, 26.9,26.2, 26.0, 19.6.

4.6.9. 1-Benzyl-2-methyl-5,5-diphenylpiperidine (Table 2, entry 8,5i). A known compound,17 95% yield, yellow oil. 1H NMR (400MHz,CDCl3, TMS): d 7.36e7.27 (m, 5H), 7.19e7.09 (m, 10H), 4.05 (d,J¼13.2 Hz, 1H), 3.35 (d, J¼12.0 Hz, 1H), 3.13 (d, J¼13.6 Hz, 1H),2.47e2.40 (m, 3H), 2.17 (dt, J¼3.2, 12.0 Hz, 1H), 1.63e1.60 (m, 1H),1.43e1.31 (m, 1H), 1.13 (d, J¼6.0 Hz, 3H). 13C NMR (100 MHz, CDCl3,TMS): d 148.9, 147.1, 139.8, 129.8, 128.7, 128.3, 128.2, 127.9, 127.3,127.1, 125.9, 125.5, 60.9, 58.8, 56.0, 46.4, 34.0, 30.8, 18.3.

4.6.10. 2-Benzyl-3-methyl-2-azaspiro[5.5]undecane (Table 2, entry 9,5j). A known compound,17 90% yield, colorless oil. 1H NMR(400MHz, CDCl3, TMS): d 7.33e7.26 (m, 4H), 7.22e7.18 (m,1H), 4.00(d, J¼13.6 Hz, 1H), 3.07 (d, J¼13.2 Hz, 1H), 2.77 (d, J¼9.6 Hz, 1H),2.52e2.43 (m, 1H), 1.86 (d, J¼9.2 Hz, 1H), 1.73 (dd, J¼7.2, 12.8 Hz,1H), 1.45e1.24 (m, 11H), 1.13 (d, J¼6.4 Hz, 3H). 13C NMR (100 MHz,CDCl3, TMS): d 140.0, 128.6, 128.0, 126.5, 66.6, 59.0, 57.9, 46.9, 39.3,39.2, 38.5, 26.0, 23.6, 23.5, 19.2.

4.6.11. 2-Benzyl-3-methyl-2-azaspiro[5.5]undecane (Table 2, entry10, 5k). A known compound,6a 90% yield, colorless oil. 1H NMR(400MHz, CDCl3, TMS): d 7.34e7.27 (m, 4H), 7.23e7.19 (m,1H), 3.99(d, J¼14.0 Hz, 1H), 3.05 (d, J¼14.0 Hz, 1H), 2.52 (d, J¼11.6 Hz, 1H),2.27e2.22 (m, 1H), 1.62 (d, J¼11.2 Hz, 1H), 1.54e1.28 (m, 10H),1.17e1.03 (m, 7H). 13C NMR (100 MHz, CDCl3, TMS): d 140.7, 128.5,128.0, 126.4, 61.6, 58.3, 57.2, 37.9, 34.8, 33.2, 30.8, 26.9, 21.6, 19.1.

4.6.12. 1-Benzyl-2-methyl-4-phenylpyrrolidine (Table 2, entry 11,5l). An unknown compound, 85% yield, yellow oil. IR (CH2Cl2) n

3062, 3030, 2962, 2853, 2567, 1684, 1602, 1495, 1453, 1375, 1080,1030, 759, 700 cm�1. 1H NMR (400 MHz, CDCl3, TMS): d 7.37e7.35(m, 2H), 7.31e7.19 (m, 7H), 7.16e7.12 (m,1H), 4.10 (d, J¼13.2 Hz,1H),3.22e3.14 (m, 2H), 2.97 (dd, J¼4.0, 10.0 Hz, 1H), 2.67e2.59 (m, 2H),2.46e2.39 (m, 1H), 1.62e1.55 (m, 1H), 1.23 (d, J¼6.0 Hz, 3H). 13CNMR (100 MHz, CDCl3, TMS): d 128.6, 128.3, 128.1, 127.2, 126.7,125.8, 61.6, 60.5, 58.0, 43.9, 41.2, 18.9. MS (%) m/z 251.2 (Mþ, 6),236.1 (100), 147.1 (4), 117.1 (4), 91.1 (35), 56.0 (10). HRMS (EI) calcdfor C18H21N requires: 251.1674. Found: 251.1673.

4.6.13. 4-Benzyl-3-methylmorpholine (Table 2, entry 12, 5m). Aknown compound,18 90% yield, yellow oil. IR (CH2Cl2) n 3084, 3062,3028, 2964, 2884, 2844, 2802, 2644, 2595, 1950, 1876, 1810, 1755,1679, 1601, 1494, 1452, 1393, 1374, 1352, 1331, 1127, 1095, 1068, 894,733, 698 cm�1. 1H NMR (400 MHz, CDCl3, TMS): d 7.33e7.29 (m,

4H), 7.25e7.22 (m, 1H), 4.06 (d, J¼13.2 Hz, 1H), 3.74e3.69 (m, 2H),3.61e3.56 (m, 1H), 3.34e3.28 (m, 1H), 3.14 (d, J¼12.8 Hz, 1H),2.60e2.57 (m, 1H), 2.51e2.47 (m, 1H), 2.22e2.16 (m, 1H), 1.09 (d,J¼6.4 Hz, 3H). 13C NMR (100MHz, CDCl3, TMS): d 138.3, 128.8, 127.9,126.7, 72.7, 67.1, 58.0, 55.2, 51.0,14.2. MS (%)m/z 191.1 (Mþ, 15),176.1(71), 160.1 (19), 132.1 (13), 91.1 (100), 65.0 (8). HRMS (EI) calcd forC12H17NO requires: 191.1310. Found: 191.1315.

4.6.14. 1-Benzyl-2,4,4-trimethylpyrrolidine (Table 2, entry 14, 5o). Aknown compound,17 88% yield, colorless oil. 1H NMR (400 MHz,CDCl3, TMS): d 7.34e7.27 (m, 4H), 7.23e7.19 (m, 1H), 4.00 (d,J¼13.2 Hz, 1H), 3.10 (d, J¼13.6 Hz, 1H), 2.63 (d, J¼8.8 Hz, 1H),2.59e2.51 (m, 1H), 1.93 (d, J¼9.2 Hz, 1H), 1.72 (dd, J¼7.2, 12.4 Hz,1H), 1.33e1.26 (m, 1H), 1.14 (d, J¼6.0 Hz, 3H), 1.07 (s, 3H), 0.97 (s,3H). 13C NMR (100 MHz, CDCl3, TMS): d 140.1, 128.7, 128.0, 126.5,66.4, 59.7, 58.0, 49.1, 35.4, 30.6, 29.2, 19.5.

4.6.15. 1-Benzyl-2,5,5-trimethylpiperidine (Table 2, entry 15, 5p). Aknown compound,19 90% yield, colorless oil. 1H NMR (400 MHz,CDCl3, TMS): d 7.37e7.32 (m, 2H), 7.29e7.25 (m, 2H), 7.20e7.17 (m,1H), 3.99 (d, J¼14.0 Hz, 1H), 3.07 (d, J¼13.6 Hz, 1H), 2.30 (dd, J¼2.0,11.2 Hz, 1H), 2.27e2.19 (m, 1H), 1.68 (d, J¼10.8 Hz, 1H), 1.59e1.44(m, 2H), 1.38e1.32 (m, 1H), 1.19e1.13 (m, 1H), 1.11 (d, J¼6.0 Hz, 3H),0.95 (s, 3H), 0.79 (s, 3H). 13C NMR (100 MHz, CDCl3, TMS): d 140.6,128.5, 128.0, 126.4, 63.8, 58.3, 56.6, 37.1, 31.6, 30.9, 28.9, 25.2, 18.9.

4.6.16. 1-Benzyl-2,4-dimethyl-4-phenylpyrrolidine (Table 2, entry 16,5q). An unknown compound, 90% yield, yellow oil. IR (CH2Cl2) n

3084, 3060, 3026, 2962, 2925, 2868, 2786, 2726, 1946, 1870, 1805,1602, 1495, 1450, 1375, 1074, 803, 763, 736, 698 cm�1.Major:minor¼1:0.6. 1H NMR (400 MHz, CDCl3, TMS, major di-astereomer): d 7.39e7.11 (m, 10H), 4.10 (d, J¼13.2 Hz, 1H),3.29e2.99 (m, 1H), 2.87e2.79 (m, 1H), 2.47e2.06 (m, 1H), 1.91 (dd,J¼9.6, 12.4 Hz, 1H), 1.35 (s, 3H), 1.18 (d, J¼5.6 Hz, 3H). 1H NMR(400 MHz, CDCl3, TMS, minor diastereomer): d 7.39e7.11 (m, 10H),4.07 (d, J¼13.2 Hz, 1H), 3.29e2.99 (m, 1H), 2.70e2.63 (m, 1H),2.47e2.06 (m, 1H), 1.69 (dd, J¼7.6, 12.8 Hz, 1H), 1.44 (s, 3H), 1.24 (d,J¼6.4 Hz, 3H). 13C NMR (100 MHz, CDCl3, TMS): d 151.4, 150.5, 140.1,140.0, 128.6, 128.1, 128.0, 126.7, 125.9, 125.8, 125.5, 125.3, 68.4, 66.9,59.9, 59.2, 58.1, 57.9, 50.5, 47.9, 43.8, 43.0, 32.5, 29.7, 20.3, 19.0. MS(%) m/z 265.2 (Mþ, 8), 250.2 (100), 147.1 (19), 91.1 (73), 56.0 (100),65.0 (77). HRMS (EI) calcd for C19H23N requires: 265.1830. Found:265.1832.

4.6.17. 1-Benzyl-2,5-dimethyl-5-phenylpiperidine (Table 2, entry 17,5r). An unknown compound, 90% yield, yellow oil. IR (CH2Cl2) n

3028, 2850, 1670, 1495, 1448, 1261, 1124, 1081, 862, 801, 698 cm�1.Major:minor¼1:0.7. 1H NMR (400 MHz, CDCl3, TMS, major di-astereomer): d 7.36e7.24 (m, 9H), 7.17e7.12 (m, 1H), 4.07 (d,J¼13.6 Hz, 1H), 3.16e3.27 (m, 2H), 2.44e1.58 (m, 6H), 1.33 (s, 3H),1.19 (d, J¼6.8 Hz, 3H). 1H NMR (400 MHz, CDCl3, TMS, minor di-astereomer): d 7.36e7.24 (m, 9H), 7.17e7.12 (m, 1H), 4.00 (d,J¼13.2 Hz, 1H), 3.16e3.27 (m, 2H), 2.44e1.58 (m, 6H), 1.28 (s, 3H),1.06 (d, J¼6.0 Hz, 3H). 13C NMR (100 MHz, CDCl3, TMS): d 149.6,147.9, 140.2, 139.8, 129.2, 128.6, 128.05, 127.98, 127.9, 127.7, 126.73,126.66, 126.5, 125.6, 125.5, 125.2, 62.1, 61.2, 58.9, 58.3, 56.5, 56.4,38.4, 37.8, 36.0, 35.6, 31.5, 31.3, 30.3, 29.7, 25.4, 19.1. MS (%) m/z279.2 (Mþ, 3), 264.2 (100), 148.1 (13), 118.1 (6), 91.1 (25). HRMS (EI)calcd for C20H25N requires: 279.1978. Found: 279.1979.

4.6.18. 2-Methyl-4,4-diphenyl-1-tosylpyrrolidine (Table 2, entry 18,5s). A known compound,11c 90% yield, white soild. 1H NMR(400MHz, CDCl3, TMS): d 7.54 (d, J¼8.4 Hz, 2H), 7.20e7.01 (m,13H),4.10 (d, J¼10.4 Hz, 1H), 3.89 (d, J¼10.8 Hz, 1H), 3.75e3.67 (m, 1H),2.71 (ddd, J¼0.8, 7.6, 12.8 Hz, 1H), 2.32 (s, 1H), 2.19 (dd, J¼4.8,12.4 Hz, 1H), 1.18 (d, J¼4.8, 6.4 Hz, 3H). 13C NMR (100 MHz, CDCl3,

R. Zhang et al. / Tetrahedron 68 (2012) 3172e31783178

TMS): d 145.6, 144.8, 143.0, 135.4, 129.5, 128.5, 127.2, 126.7, 126.5,126.4, 126.2, 58.4, 55.4, 52.3, 46.0, 22.1, 21.5.

4.6.19. 1,2-Dibenzyl-4,4-diphenylpyrrolidine (Table 2, entry 19,5t). An unknown compound, 95% yield, colorless oil. IR (CH2Cl2) n3029, 2851, 1672, 1492, 1448, 1261, 1124, 1081, 861, 804, 699 cm�1.1H NMR (400 MHz, CDCl3, TMS): d 7.39e7.31 (m, 4H), 7.27e7.15 (m,10H), 7.13e7.09 (m, 6H), 4.06 (d, J¼13.2 Hz, 1H), 3.74 (d, J¼9.6 Hz,1H), 3.38 (d, J¼13.2 Hz, 1H), 3.12e3.05 (m, 1H), 2.90 (dd, J¼4.4,13.2 Hz), 2.81 (d, J¼10.0 Hz, 1H), 2.71 (dd, J¼8.4, 12.8 Hz, 1H), 2.42(dd, J¼9.2, 12.8 Hz, 1H), 2.33 (dd, J¼10.0, 13.2 Hz, 1H). 13C NMR(100 MHz, CDCl3, TMS): d 149.4, 148.1, 140.0, 139.9, 129.3, 128.6,128.3, 128.1, 127.9, 127.3, 127.1, 126.9, 125.9, 125.8, 125.5, 65.7, 65.3,59.0, 52.7, 44.3, 41.3. MS (ESI) m/z: 426 (MþþNa, 100). HRMS (ESI)calcd for C30H29NNa requires: 426.2198. Found: 426.2196.

Acknowledgements

We thank the Shanghai Municipal Committee of Science andTechnology (11JC1402600), National Basic Research Program ofChina (973)-2009CB825300, the Fundamental Research Funds forthe Central Universities and the National Natural Science Founda-tion of China for financial support (21072206, 20472096, 20872162,20672127, 21121062 and 20732008).

Supplementary data

The 1H and 13C NMR spectroscopic data and charts of thecompounds and X-ray crystal data of complex 3 are included in theSupplementary data. Supplementary data related to this article canbe found online at doi:10.1016/j.tet.2012.02.060.

References and notes

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15. The crystal data of NHCePt complex 3 have been deposited in CCDC withnumber 741879. Empirical Formula: C36H28I2N4OPt; Formula Weight: 981.51;Crystal Color, Habit: colorless, prismatic; Crystal Dimensions: 0.289�0.112�0.078 mm; Crystal System: Monoclinic; Lattice Type: Primitive; Lattice Parame-ters: a¼12.9388(13) �A, b¼9.0856(9) �A, c¼14.7605(14) �A, a¼90� , b¼106.522� ,g¼90� , V¼1663.6(3) �A3; Space group: P2(1); Z¼2; Dcalcd¼1.959 g/cm3;F000¼928; Diffractometer: Rigaku AFC7R; Residuals: R; Rw: 0.0586, 0.1504.

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