Oxygen greatly accelerates the generation of the bromocarbenoid reagent of zinc from diethylzinc and bromoform. Olefins, including cyclohexene, cyclooctene, 1-hexene, cis-and trans-2-butene, isobutene, and 2-methyl-2-butene were bromocyclopropanated in yields of ca. 60–85% using a diethylzinc-bromoform-oxygen system. The bromocarbenoid showed high syn-selectivity for the addition to cyclooctene and cis-2-butene. 9-Bromo-9-deutero [ ...
