Ionic addition of t-butyl N,N-dibromocarbamate (BBC) to alkenes and cycloalkenes

The addition of t-butyl N,N-dibromocarbamate (BBC) to alkenes and cycloalkenes in the presence of BF3·Et2O proceeds smoothly at −20°C in CH2Cl2 affording upon reduction with aqueous Na2SO3 the corresponding β-bromo-N-Boc-amines. Immediate deprotection of these adducts with gaseous HCl yields β-bromoamine hydrochlorides in moderate yields. The regioselectivity typical for Markovnikov addition was observed for styrene. Stereospecific anti-addition of BBC to cyclohexene and (E)-hex-3-ene, as proven by 1H NMR evidence, is compatible with an ionic addition pathway and can be rationalized by assuming the intermediate complex formation between BBC and BF3.