REACTIONS OF CARBENE INTERMEDIATES FROM THE REACTION OF TRIALKYL PHOSPHITES WITH DIALKYL BENZOYLPHOSPHONATES - INTRAMOLECULAR CYCLIZATIONS OF 2-SUBSTITUTED DIALKYL BENZOYLPHOSPHONATES

The reaction of dialkyl benzoylphosphonates 1 with trialkyl phosphites leads to the formation of carbene intermediates 3 via the anionic int ermediates 2. The carbene intermediates 3 (R = 2-PhO, 2-PhOCH(2), and 2-PhS) have been generated by heating the corresponding 2-substituted dialkyl benzoylphosphonates with trimethyl phosphite and their subsequ ent reactions investigated. Reactions proceed either by intermolecular trapping of the carbene intermediates by trimethyl phosphite to give novel ylidic phosphonates 4, or by intramolecular routes involving car bene insertion into the pi-system of the phenyl ring in the substituen t, Studies using methyl-substituted derivatives have shown that the fo rmation of the thioxanthenylphosphonate 15 (X = S, R' = R '' = Me) pro ceeds via a spiro diene intermediate 14(X = S, R' = R '' = Me).