Modified salen catalysts in atom-economic reactions: Enantioselective carbonyl-ene and Nazarov cyclization reactions.

摘要

Chiral metal salen complexes are a family of kinetically non-labile catalysts that have been utilized in a number of enantioselective reaction. This thesis discusses the development of the first highly enantioselective salen-catalyzed carbonyl-ene reaction and Nazarov cyclization reaction. Chiral 3,3'-trialkylsilyl-substituted cobalt salens were discovered to promote the carbonyl-ene reaction of various 1,1-disubstituted and trisubstituted alkenes with ethyl glyoxylate and pyridine carboxaldehyde. The reactions proceed at room temperature using catalyst loadings as low as 0.1 mol% and produce unsaturated-&agr-hydroxy carboxylic esters in excellent yields, enantioselectivities, and diastereoselectivities. In addition, a new class of 5,5'-(2,4,6-trialkyl)aryl chromium salen complexes were demonstrated as effective catalysts in the Nazarov electrocyclization of both enol-derived dienones and unactivated dienones. This is the first asymmetric catalytic cyclization of unactivated dienones. Chromium salens catalyze the cyclization of simple divinyl ketones generating cyclopentenones with up to three new stereocenters in good yields and excellent diastereo- and enantioselectivities. Appendices A and B contain crystal structure data for the Co (III) TIBS SbF6 complex and NMR spectral data for synthesized compounds.