Diastereoselective ring cleavage of azetidines with cyanogen bromide

N-alkyl azetidines bearing a chiral substituent at the nitrogen atom, and variable C-3 as prochiral centre, react readily with cyanogen bromide even low temperatures to produce corresponding 3-bromo-N-cyanamides diastereoisomeric mixtures via ring opening. This reaction was found be diastereoselective (up 80:20 dr). In one case, major diastereomer could isolated by recrystallization, configuration of newly created stereocentre determined X-ray crystallography.