Arsonium Ylides

Abstract

This chapter discusses the methods of preparation of arsonium ylides from arsonium salts and their structure, physical properties, chemical reactions, and syntnetic applications. This experiment marked the birth of the Wittig reaction, a novel method for the conversion of carbonyl groups to olefins, and the entry of ylides into the arsenal of important synthetic tools. Treatment of an aqueous alcoholic solution of 9-fluorenyltriphenylarsonium bromide with dilute ammonia or dilute sodium hydroxide afforded fluorenylidene-(9)-triphenylarsorane. A facile method for the preparation of a variety of stabilized arsonium ylides in good yield has been developed by the action of active methylene compounds with tertiary arsine oxide or tertiary arsine dihalide. Arsonium ylides have also been prepared from the decomposition of diazonium compounds in the presence of a tertiary arsine. The reaction products of carbomethoxymethylene triphenylarsorane with tetrafluoroethylene and with perfluoropropylene on passing through an alumina column gave rise to the corresponding fluoroacyl derivatives. The ultraviolet spectra of some stable arsonium ylides are studied. The π-ionization energies of arsonium ylides are very low, as is typical for ylides. Phosphonium ylides that bear an electron-withdrawing substituent in the alkylidene moiety show considerably reduced nucleophilicity, and in many cases, will not react with carbonyl groups. The nature of the arsonium substituents also influences the course of the reaction. The reactions of benzoyl, acetyl, and carbethoxymethylene triphenylarsorane with diphenylcyclopropenone in benzene afforded 2-pyrones. Current results indicate that stabilized arsonium ylides, such as phenacylide, carbomethoxymethylide, cyanomethylide, fluorenylide, and cyclopentadienylide, afford only olefinic products upon reaction with carbonyl compounds.