An Expedient Synthesis of Vicinal Diamines from Alkenes and Cycloalkenes

A new procedure for the facile preparation of various vicinal diamines is developed that utilizes diethyl N-(β-bromoalkyl)phosphoramidates 2 easily accessible by ionic addition of diethyl N,N-dibromophosphoramidate (DBPA) to alkenes and cycloalkenes 1. Crude phosphoramidates 2 are readily transformed into the corresponding ammonium ditosylates 5 by sequential azidation, Staudinger reaction with triethyl phosphite, and deprotection by refluxing with p-toluenesulfonic acid in aqueous ethanol. Diamination of cyclohexene and indene proceeds stereospecifically affording cis-1,2-diaminocyclohexane and cis-1,2-diaminoindane, respectively. Open-chain olefins do not react stereospecifically under conventional conditions yielding mixtures of diastereoisomers. Full stereochemical control of azidation can be, however, achieved when β-bromoamine hydrochlorides instead of diethyl N-(β-bromoalkyl)phosphoramidates are used as starting materials for this reaction.