Effect of solvent polarity on N–H insertion versus rearrangement of alkylidene carbenes

Alkylidene carbenes, when generated from o-aminobenzophenones and lithiated trimethylsilyldiazomethane, give a mixture of alkyne (by rearrangement) and indole (by N–H insertion). It has been found that this ratio of indole to acetylene shows a linear dependence on the polarity of the ethereal solvent.