STEREOSELECTIVE ALKENYLATION OF ALDEHYDES WITH PHOSPHORUS CARBANIONS - PREPARATION OF E-2-ALKOXY-2-ALKENOATES AND Z-2-ALKOXY-2-ALKENOATES AND 2-ARYLOXY-2-ALKENOATES

Eighteen phosphorus-based alkerrylation reagents 1a-6c were synthesize d and condensed with n-butyraldehyde 7a and benzaldehyde 7f. They were condensed with the aldehydes 7b-e,g-n to produce 2-methoxy-2-alkenoat es 8a-n and 2-phenoxy-2-alkenoates 9a-n. A discussion on different sel ectivities for the alkerrylation reagents under different experimental conditions (base, soh em, temperature), the influence of the aldehyde s on the geometrical outcome (electron rich or poor substituents steri c hindrance) and the selection of the most E-and Z-selective reaction conditions for each class of aldehydes are reported Namely, triphenyl phosphonium salt la at RT in THF with DBU was better for Z-selectivity while trifluoroethylphosphonates 5b, 6b and 6c at -78 degrees in THF with KN(SiMe3)(2) were better for E-selectivity. (C) 1997 Elsevier Sci ence Ltd.