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.