Synthesis of E- and Z-vinyl ethers by the Horner–Wittig reaction

Abstract

Diphenyl(methoxymethyl)- and diphenyl-(1-methoxyethyl)-phosphine oxides form lithium derivatives which add to aldehydes and ketones. The adducts may be separated into crystalline diastereoisomers each giving a single geometrical isomer of a vinyl ether on treatment with base. Hydrolysis of the vinyl ethers provides a reliable aldehyde synthesis in which the lithium derivative (19) behaves as a formyl anion equivalent. The method has been used to convert an acyl indole into a vinyl ether in compounds related to the strychnos alkaloids.