Chirality breeding via asymmetric phosphination. Palladium-catalyzed diastereoselective synthesis of a P-stereogenic phosphine

摘要

Methylation of the crystallographically characterized primary alkylphosphine-borane PH(2)Men(BH3) (3, Men = (-)-menthyl) under phase-transfer conditions, followed by deprotection, gave the secondary phosphine PH(Me)(Men) (2). Cross-coupling of 2 with PhI in the presence of NaOSiMe3 selectively gave S-P-PPh(Me)(Men) (1, L) with a variety of Pd catalyst precursors, including a complex of diastereopure S-P-1, trans-PdL2(Ph)(I) (6a). In this reaction, the chiral phosphine L formally acted as a ligand in catalysis of its selective self-reproduction, but 6a was partially transformed to its diastereomers, trans-Pd(S-P-1)-(R-P-1)(Ph)(I) (6b) and trans-Pd(R-P-1)(2)(Ph)(1) (6c), and several other intermediates were observed during catalysis.