Simple large-scale preparation of 3,3-disubstituted cyclopropenes: Easy access to stereodefined cyclopropylmetals via transition metal-catalyzed hydrometalation

3,3-Disubstituted cyclopropenes have been readily prepared in a multigram scale via two different methods: (1) dehydrohalogenation of bromocyclopropanes, and (2) Rh-catalyzed addition of carbenoids to trimethylsilylacetylene followed by desilylation. Highly diastereoselective Pd-catalyzed hydrostannation and highly enantioselective Rh-catalyzed hydroboration of 3,3-disubstituted cyclopropenes afforded useful cyclopropylmetal building blocks in high yields.