P-chiral 1,7-diphosphanorbornenes: synthesis and application in asymmetric allylic alkylation

Abstract

Oxidation of P-chiral 1,7-diphosphanorbornene 2 by atmospheric oxygen at 25°С or sulfurization with elemental sulfur at 80°С result in formation of enantiopure mixed-valent P^III, P^V 7-oxo(thia)-1,7-diphosphanorbornenes 3, 4 with high regioselectivity. The catalytic activity for the prepared enantiopure monodentate phosphines with rigid bicyclic [2.2.1] structure was evaluated in Pd-catalyzed asymmetric allylic substitution of rac-1,3-diphenylallyl acetate with dimethyl malonate. Selective oxidation of the bridgehead phosphorus atom in 1,7-diphosphanorbornene 2 allows increasing the enantioselectivity of allylic alkylation from 14% to 63% ee.

Graphical Abstract

Keywords:

• Chiral phosphine
• P-stereogenic
• caged phosphine
• asymmetric catalysis
• allylic alkylation

Acknowledgments

Experimental work was carried out by the government assignment for FRC Kazan Scientific Center of RAS. The authors gratefully acknowledge the Assigned Spectral-Analytical Center of FRC Kazan Scientific Center of RAS.