REACTION OF ALDEHYDES WITH STABILIZED SULFUR YLIDES - HIGHLY STEREOSELECTIVE SYNTHESIS OF 2,3-EPOXY-AMIDES

Reaction of benzaldehyde (1a), 4-chloro-benzaldehyde (1b), or 3-nitro-benzaldehyde(1c), with N,N-dimethyl-2-(dimethylsulfuranylidene)acetamide (2), gives only the trans-3-phenyl-2,3-glycidamide derivatives 3a-c in good yields. The same reaction with 2-nitro-benzaldehyde (1d), gives a 15:1 mixture (trans-cis) of analogous products 3d. Reaction of 2 with 2,3-O-isopropylidene-D-glyceraldehyde (4) results in a highly stereoselective synthesis of (2S,3R,4R)- and (2R,3S,4R)-N,N-dimethyl-2, 3-epoxy-4,5-o-isopropylidene-4,5-dihydroxypentanoamides (5a) and (5b), (86:14 at r.t., 96:4 at -5 to 0°C, 5a:5b). Configurational analysis was made by three different methods: 1) 1H-NMR coupling constants analysis; 2) comparison with the cis-trans analogous 15a,b and 7a,b, prepared by epoxidation of the cis or trans alkenes 13 and 12; and 3) the transformation of the 5a, 7a and 15a (or 5b,7b and 15b) isomers into the known (3S,4R)-3,4,5-trihydroxypentanoic acid 1,4-lactone (10a) (or 3(R)-isomer, 10b respectively). © 1990.