Flash vacuum pyrolysis of stabilised phosphorus ylides. Part 4. Stepwise construction of terminal 1, 3-diynes, conjugated diacetylenic esters and a triacetylenic ester

Thirteen examples of stabilised alkynoyl ylides 6 have been prepared and are found, upon flash vacuum pyrolysis (FVP) at 500 degrees C, to undergo extrusion of Ph(3)PO to give the diacetylenic esters 7 in moderate yield. At 750 degrees C the same ylides afforded terminal 1.3-diynes 8 although often in poor yield. For R = 2-MeSC(6)H(4) both 7 and 8 undergo secondary loss of Me(.) and cyclisation to give 2-alkynylbenzothiophene derivatives 9 and 10 in low yield. The first example of an alkadiynoyl ylide 11 has been prepared and is converted by FVP at 500 degrees C into the triacetylenic ester 12.