One-pot transformation of cyclic phosphine oxides to phosphine-boranes by dimethyl sulfide-borane

Different types of cyclic phosphine oxides, such as tetrahydrophosphole oxi de 1, phosphabicyclo[3.1.0]hexane 3-oxide 8 and phosphabicyclo[2.2.1]hepten e 7-oxides 10 and 12 were efficiently converted to phosphine-boranes 2, 9, 11 and 13, respectively, under relatively mild conditions by reaction with 4.4 equivalents of dimethyl sulfide-borane. The more strained hetero-ring t he starting phosphine oxide (in general 16) has, the easier to accomplish t he change in the P-function, that takes place through the corresponding pho sphine intermediate (20). It is noteworthy that the imide carbonyl groups i n starting materials 10 and 12 were fully reduced by the borane to give 11 and 13 respectively.