Erythro phosphinyl alcohols 3 and the threo isomers 4 give (E)- and (Z)-alkenes, respectively, by an anti elimination in contrast to the syn HornerâWittig elimination of the corresponding phosphinoyl alcohols.
The reduction of an α-alkyl-β-ketophosphine oxide with LiBH4 in presence of a strong chelating agent, such as TiCl4, gives the corresponding β-hydroxyphosphine oxide in high yields and with high anti-diastereoselectivity independently from the size of both the α- and β-alkyl chains.
Stereochemically pure E- and Z- alkenes by the Wittig–Horner reaction
作者:Antony D. Buss、Stuart Warren
DOI:10.1039/c3981000100b
日期:——
Pure Z-alkenes are obtained stereospecifically from erythro-alcohols (3) formed on addition of Ph2PO-stabilised anions to aldehydes; acylation of the same anions, reduction of the α-Ph2P(O) ketones (5) to the threo-alcohol (6), and elimination gives pure E-alkenes.