SYNTHESIS AND DEPROTECTION OF [1-(ETHOXYCARBONYL)-4-[(DIPHENYLMETHOXY)CARBONYL]-1-METHYL-2-OXOBUTYL]-TRIPHENYLPHOSPHONIUM CHLORIDE - A KEY INTERMEDIATE IN THE WITTIG REACTION BETWEEN A CYCLIC ANHYDRIDE AND A STABILIZED YLIDE

[l-(Ethoxycarbonyl)-4-[(diphenylmethoxy)carbonyl]-l-methyl-2-oxobutyl]triphenylphosphonium chloride (16) has been synthesized as an unstable oil. Removal of the (diphenylmethoxy)carbonyl group gave E enol lactone 5 stereoselectively and without evidence of phosphonium salt 8. When enol lactone formation is not favored as with phosphonium salt 27, loss of triphenylphosphine oxide occurs to yield an allene. Phosphonium salts 16, 17,18,20, and 35 have also been shown to yield an allene on treatment with base. The chemistry of these derivatives and the mechanism of enol lactone and allene formation is discussed. Phosphonium salts such as 8 and 27 are postulated as key intermediates in the Wittig reaction between a cyclic anhydride and a stabilized ylide. © 1990, American Chemical Society. All rights reserved.