N -►C-Migration of halogen

In 1972, Queguiner and co-workers established that treatment of 3-bromopyridine in excess with n-BuLi at low temperatures results in the formation of a halogen migration product, the 4-bromo isomer [72CR(C)(275) 1439]. 

P-450 has been shown to catalyze epoxidation with retention of the olefin configuration (114). Ortiz de Montellano and co-woiicers have shown that heme N-alkylation accompanies epoxidation when terminal olefins are oxidized by P-450 (775). Further, the oxidation of 1,1,2-trichloroethylene is known to give trichloroacetaldehyde along with epoxide (776, 777). A mechanism that explains simultaneous epoxidation, heme alkylation, and halogen migration is depicted in Scheme XVI (777). In this process, initial electron transfer affords a transient rr-radical cation that can collapse with C-0 bond formation to give either radical or cation intermediates. 

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