Boron trifluoride ionic dissociation

The anti addition of diethyl 7V,Ar-dibromophosphoramidates to acyclic and cyclic alkenes was achieved in the presence of boron trifluoride, which makes the ionic dissociation of the N —Br bond more labile94,9s. After reduction of the initial /J,lV-dibromo adducts with sodium bisulfite, the /i-bromo-A -hydrophosphoramides 3 precursor of / -bromo amine hydrochlorides 4 were obtained (Table 4). However, a mixture of diastereomers was obtained from (Z)-l-phenyl-l-propene and (E)- and (Z)-l,2-diphenylethylene. Direct assignment of stereochemistry by H NMR of the phosphoroamidates derived from 2-butenes was not possible. Detailed analysis is, however, possible for the H-NMR spectra of the /J-bromo amine hydrochlorides. As determined by 31P NMR spectroscopy all additions to unsymmetrical aliphatic alkenes were not regiospecific. The /f-bromo amine hydrochlorides were converted to 1,2-diamines95. 

---