Preparation of P‐amino‐3‐phosphabicyclo[3.1.0]‐hexane 3‐oxides either by addition of dichlorocarbene to the double bond of 1‐amino‐2,5‐dihydro‐1H‐phosphole 1‐oxides or by substitution of the P‐chloro derivative of the bicyclic system was accomplished. Two different diastereomers are obtained by the two approaches; their 13C NMR spectra were interpreted on the basis of the P‐ethoxy isomers, whose structures were confirmed by X‐ray analysis. The P‐hydroxy adduct was also prepared, and it was found that intermolecular OH … O hydrogen bonding connects the molecules together in the solid phase. This effect eliminates the possibility of diastereoisomerism, as was also observed in the case of P‐hydroxy tetrahydrophosphinine oxides. Thermolysis of the P‐hydroxy adduct is a better way to synthesize 1‐hydroxy‐1,2‐dihydrophosphinine oxides than by hydrolysis of the phosphinic chlorides.
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