A [2+2+1] strategy for the conversion of olefins into cyclopentenones. Ring expansion of 2-N-methyl-N-tosylcyclobutanones

Article abstract of DOI:10.1016/S0040-4039(99)00948-X

α-N-Methyl-N-tosylcyclobutanones prepared by asymmetric cycloadditions of the corresponding keteniminium triflate to olefins have been converted into a mixture of epoxides using dimethylsulfonium ylide. Treatment of these epoxides with lithium iodide unexpectedly yielded the corresponding cyclopentenones. This sequence amounts to a [2+2+1] cyclopentannulation of an olefin.