Systematic Evaluation of 1,2-Migratory Aptitude in Alkylidene Carbenes

Alkylidene carbenes undergo rapid inter- and intramolecular reactions rearrangements, including 1,2-migrations of β-substituents to generate alkynes. Their propensity for substituent migration exerts profound influence over the broader utility alkylidene carbene intermediates, yet prior efforts categorize 1,2-migratory aptitude in these elusive species have been hampered by disparate modes generation, ultrashort lifetimes, mechanistic ambiguities, need individually prepare a series 13C-labeled precursors. Herein we report on rearrangement 13C-alkylidene generated situ homologation carbonyl compounds with [13C]-Li-TMS-diazomethane, an approach that obviates isotopically labeled substrates has expedited systematic investigation (13C{1H} NMR, DLPNO-CCSD(T)) migratory aptitudes unprecedented range more than 30 carbenes. Hammett analyses 26 differentially substituted benzophenones reveal several counterintuitive features 1,2-migration may prove study synthetic application unsaturated generally.