STERIC COURSE OF CONVERSION OF SOME BROMOHYDRINS INTO DIBROMIDES WITH PHOSPHORUS TRIBROMIDE AND THIONYL BROMIDE

The conversion of (S)-(-)-2-bromo-1-butanol into 1,2-dibromobutane with SOBr2, SOBr2-pyridine. and PBr3 was investigated. While the reactions with SOBr2 produced dibromides with low specific rotations (positive in the absence and negative in the presence of pyridine), PBr3 gave a levorotatory product with much higher optical activity. Equilibrated mixtures of trans-dibromides were obtained in the reactions of the 4-t-butylcyclohexene trans-diaxial bromohydrins with SOBr2 and SOBr2-pyridine, whereas with PBr3 the dibromide was more than 90% diaxial. It can be deduced from the data that (-)-1,2-dibromobutane almost certainly has the (S) configuration. Asymmetric bromination of 1-butene in the presence of dihydrocinchonine afforded dextrorotatory 1,2-dibromobutane. © 1969.