Development and synthesis of novel organocatalysts

Abstract

The unfavourable use of metal-based catalysts in organic synthesis can be overcome by using small organic molecules; organocatalysts. Herein we report the development and synthesis of a novel range of organocatalysts derived from amino acids incorporating imidazole, thiourea and phosphoramide moieties to confer the capability to act as bifunctional organocatalysts. Our organocatalyst, a phosphoramide derived from valine, showed initial success in the catalytic allylation of aldimine with allyltrichlorosilane, producing 40% ee. Oxazoline catalysts derived from 2-pyridines have been shown to be effective activators of trichlorosilane for the reduction of ketones and ketimines. The reaction however suffered from chloride promoted ring opening of the catalyst. By replacing the oxygen of the oxazoline moiety with sulphur we were able to successfully avoid this problem. Further expansion of the substrate scope was achieved, heterocyclic imines were reduced in good enantioselectivity, up to 89% ee