THE REACTION OF METHYLIDENETRIPHENYLPHOSPHORANE WITH AROMATIC AND HETEROCYCLIC 1,2-DIKETONES

Whereas treatment of both 2,2,6-trimethylthiochromane-3,4-dione (1a) and 3,3,6,8-tetramethyl-1,2,3,4-tetrahydronaphthalene-1,2-dione (1b) with 1 mol equivalent of Ph3P=CH2 (2) affords a 1,2-methylidene ketone (3) which on reaction with a further mol equivalent of 2 gives a 1,2-diphenylphosphinoylethyl ketone (7), direct treatment of 1a and 1b with 2 mol equivalent of 2 causes a ring contraction to occur, resulting in a resonance-stabilised ylide (10).