Flash vacuum pyrolysis of stabilised phosphorus ylides. Part 2. Two-step conversion of acid chlorides into acetylenic esters and terminal alkynes

Abstract

The known thermal extrusion of Ph₃PO from α-acyl-α-ethoxycarbonyl ylides 1 to give acetylenic esters 2 can be accomplished in excellent yield by using flash vacuum pyrolysis (FVP) at 500 °C. Upon raising the furnace temperature to 750 °C, this reaction is accompanied by the unexpected loss of the ethoxycarbonyl group to give the terminal alkynes 7 in moderate yield. A mechanism is proposed for this reaction based on isotopic labelling studies. Ten new examples of ylides 1 have been prepared for the first time.