Synthesis of Spiro[2.2]pentanes and Vinylcyclopropanes Using Sulfones as Carbene Equivalents

Spiro[2.2]pentanes are rigid carbocycles with well-defined exit vectors and high F(sp³), which makes them intriguing functional groups for medicinal chemistry campaigns. The high degree of strain present in these compounds, however, precludes the use of traditional cyclopropanation methodologies for the synthesis of densely functionalized spiropentane derivatives, making them difficult to obtain. Herein, we report a strategy for the synthesis of substituted arylspiro[2.2]pentanes (16 examples, 24-81% isolated yield) using sulfones as carbene equivalents. During the study, an unexpected formal C-H insertion process was observed when utilizing cyclopropyl sulfone anions as cyclopropylidene equivalents (14 examples, 24-79% isolated yield). Deuterium-labeling studies suggest that the vinylcyclopropane products arise from a stepwise addition-elimination/isomerization pathway.