2008

Pyran derivativesR 0340 Enantioselective Assembly of Substituted Dihydropyrones via Organocatalytic

Reaction in Water Media. — The two step method includes addition of aldehydes to α-keto-α,β-unsaturated esters, catalyzed by diarylpropynol ether and AcOH in water, to afford the cyclic hemiacetals, followed by oxidation with PCC or Dess—Martin per-iodinane to yield the desired dihydropyrones with high enantioselectivity. The reaction is applicable to functionalized β-arylenones (V) and is insensitive to the (E)- or (Z)-structure of the substrates. The reaction of β,γ-unsaturated esters requires the use of benzoic acid instead of AcOH [cf. (XIII)]. — (WANG, J.; YU, F.; ZHANG, X.; MA*, D.; Org. Lett. 10 (2008) 12, 2561-2564; State Key Lab. Bioorg. Nat. Prod. Chem., Shanghai Inst. Org. Chem., Acad. Sin., Shanghai 200032, Peop. Rep. China; Eng.) — R. Steudel

45- 143

2008