Synthesis and Molecular Structure of [beta]-Phosphinoyl Carboxamides: An Unexpected Case of Chiral Discrimination of Hydrogen-Bonded Dimers in the Solid State

A series of N,P,P-trisubstituted aminophosphanes react with diphenylcyclopropenone to afford an easily separable mixture of two diastereomeric [alpha],[beta]-diphenyl-[beta]-phosphinoyl carboxamides in good yields. X-ray crystal structures reveal that these compounds associate into dimers, formed from two enantiomeric units linked by two bifurcated hydrogen bonds, whereby the oxygen atom of the phosphoryl group acts as a dual acceptor for the vicinal NH and CH of a carbonyl group of a neighbouring molecule. Studies on the interconversion between diastereomeric phosphinoyl carboxamides in basic solution show that the thermodynamically most stable isomer depends on the nature of the substituent at the nitrogen atom. Simple computational calculations explain this phenomenon.