Totally diastereoselective synthesis of new P-chirogenic o-trimethylsiloxyaryl diazaphospholidines and o-hydroxyaryl diazaphospholidine–borane complexes

The totally diastereoselective synthesis of several P(III)-chirogenic o-trimethylsiloxyaryl diazaphospholidines 4 was achieved by exchange reactions in refluxing toluene from the key intermediates, o-trimethylsiloxyaryl bis(dimethylamino) phosphines 2, and various chiral diamines 3. In the case of the use of a non-C2-symmetric chiral auxiliary such as (S)-2-anilinomethylpyrrolidine (3a), compounds 4a–g, containing a stereogenic phosphorus atom, were obtained in diastereomerically pure form as the thermodynamic anti-diastereomers. Complexation of the diazaphospholidines 4 by borane-dimethylsulfide and subsequent methanolysis of the siloxy ether function lead to the formation of the desired o-hydroxyaryl diazaphospholidine-borane complexes 5 in good yields, ranging from 71 to 86%.