On the preparation of (E)- and (Z)-stilbene from the diastereoisomeric 1,2-diphenyl-2-diphenylphosphinoylethan-1-ols

Abstract

(1RS,2SR)-1,2-Diphenyl-2-diphenylphosphinoylethanol(erythro-isomer)(1) and its threo-isomer (2) have been prepared stereospecifically by opening the appropriate stilbene oxides with Ph₂PLi followed by oxidation with H₂O₂–AcOH. Compounds (1) and (2) can also be obtained stereoselectively (erythro-isomer predominating)via treatment of Ph₂POCHLiPh with PhCHO.

Under all the conditions tried, treatment of the threo-isomer (2) with base gave (E)-stilbene. The erythro-isomer (1) under most conditions gave predominantly (E)-stilbene, together with variable amounts of Ph₂POCH₂Ph, though in one case mainly (Z)-stilbene was formed. The conversion erythro-(E)-stilbene was shown to occur via fragmentation to Ph₂POCHLiPh and PhCHO by trapping experiments using m-chlorobenzaldehyde.