Asymmetric synthesis of amines by the catalytic enantioselective additions of hydrazoic acid to ketenes

Abstract

The development of a planar-chiral catalyst for the enantioselective additions of HN3 to hindered ketenes was investigated. It was demonstrated that a new planar-chiral catalyst (1.5) is an excellent catalyst for the enantioselective addition of HN3 to hindered ketenes, en route to enantioenriched amines. The addition of HN3 to a ketene is likely occurring by the Bronsted acid catalysis mechanism. The evidence in support of the Bronsted acid catalysis mechanism include stereochemical and spectroscopic results, which are consistent with data from other additions believed to occur by the Bransted acid catalysis mechanism. Enantioenriched amines generated are a family of compounds distinct from the products yielded by earlier Bronsted acid catalyzed processes. In addition, with the use of highly acidic HN3, the pH range in which a planar-chiral catalyst can function as a Bransted acid catalyst was demonstrated to be much larger than previously known. ... The development of a tertiary amine catalyst for the enantioselective additions of HN3 to unhindered ketenes was investigated. Preliminary results indicate that catalyst 2.3a exhibits promising enantioselectivity for the addition of HN3 to unhindered ketenes and appears to be complementary to planar-chiral catalyst 1.5 in terms of substrate scope. ...