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J . Org. Chern., Vol. 40, No. 16, 1975
Baccolini and Todesco
Trichlorosilane Reduction of Some Diazaphospholene Oxides Graziano Baccolini* and Paolo E. Todesco
istituto di Chimica Organica, Universita' di Bologna, Viale Risorgimento, 4, Bologna 40136, Italy Received February 18,1975 Trichlorosilane reduction of pure diazaphospholene oxides gives mixtures of cis and trans isomers of the corresponding phosphines; their configuration has been deduced from their NMR spectra. The lack of stereospecificity is explained in terms of formation of pentacoordinate phosphorus intermediates. Stereomutation of the starting phosphine oxides is observed on treatment with hexachlorodisiloxaneas well as with silicon tetrachloride. In the initiation of a general program designed to explore the synthesis,' chemical reactions, and physical properties of some derivatives of 1,2-diaza-5-phospholene 3-oxide which represent the first cases of a new heterocyclic system, we were prompted to investigate the trichlorosilane reduction of these compounds. Several years ago, trichlorosilane was introduced as a reagent with high stereospecificity for reducing phosphine oxides to phosphines2 and the method has since found wide use.3 We have found that also the diazaphospholene oxides 1 react with HSiCl3 in the presence of triethylamine in benzene solution to afford the corresponding phosphines 2 but with lack of stereospecificity. Reduction of the pure cis4 or trans isomers of 1 with trichlorosilane under identical conditions gives mixtures of different proportions of cyclic phosphines, cis-2 and trans-2.
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