Synthesis and stereochemistry of some 3-substituted 2-methylbut-2-enoic acid derivatives

Abstract

U.v. irradiation of diethyl (E)-2,4,5-trimethyl-3-oxahex-4-enedioate gives the (Z)-isomer. The n.m.r. spectra of these two isomers and of other 3-substituted 2-methylbut-2-enoic acid derivatives are discussed. Diethyl (E)-2,4,5-trimethyl-3-oxahex-4-enedioate, identical with a product from the oxidation of ethyl α-methylacetoacetate by lead dioxide, has been synthesisedfrom ethyl (E)-3-halogeno-2-methylbut-2-enoates by highly stereo-selective substitution reactions, and further reactions of this type are described. The base-catalysed addition of ethanol to ethyl 2-methylbuta-2,3-dienoate is also highly stereoselective and gives ethyl (E)-3-ethoxy-2-methylbut-2-enoate.

The oxidation of mixtures of (E)- and (Z)-3-halogeno-2-methylbut-2-enals is described.