Reactions of carbene intermediates from the reaction of trialkyl phosphites with dialkyl benzoylphosphonates: Intramolecular cyclisations 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 intermediates 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 subsequent 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 carbene insertion into the pi-system of the phenyl ring in the substituent, Studies using methyl-substituted derivatives have shown that the formation of the thioxanthenylphosphonate 15 (X = S, R' = R '' = Me) proceeds via a spiro diene intermediate 14(X = S, R' = R '' = Me).