Regioselective and stereoselective Diels -Alder reactions via a one or two metal center template.

摘要

The Diels-Alder (DA) reaction is perhaps the most powerful and versatile reaction in the synthetic chemist's arsenal, in part because of the continuous evolution of strategies to improve reactivity and selectivity. A new strategy has been developed to control Diels-Alder reactions based on simultaneous coordination of the diene and dienophile components to a Lewis acid to achieve both self-assembly and catalysis of the reaction. In this thesis the results of a systematic study to identify conditions for high selectivity are reported. Compelling evidence is presented that the mechanism for selective cycloaddition of C-1 allylic and homoallylic dienols 1a-4a involves Lewis acid catalyzed reaction of a self-assembled complex.*.;It has been established that 1-hydroxymethyl-1,3-butadienes participate in LACASA-DA (Lewis acid catalyzed and self-assembled Diels-Alder) reactions with methyl acrylate 172. However intrinsic electronic effects must now be considered when applying the strategy to 2-hydroxymethyl-1,3-butadienes. "Do 2-hydroxymethyl-1,3-butadienes participate in Diels-Alder reactions via self-assembly of the components on a Lewis acid template?" To assess the directing effect of a C-2 hydroxymethyl group via a LACASA-DA pathway, DA reactions with dienes 5-8 were conducted. The directing effect of a C-2 hydroxymethyl group via a LACASA-DA pathway was modest at best. It was evident that the high meta regioselectivity observed during DA reaction of 2-(hydroxymethyl)-1-alkyl-1,3-butadienes with methyl acrylate (MAC) was a result of the activating group at the C-1 position; not a LACASA-DA or hydroxy-directing Diels-Alder (HDDA) effect. Substituents on the butadiene moiety may control the regioselectivity of DA reactions with MAC, but the presence of a LACASA-DA effect was still apparent.*.;The next objective was to establish an enantioselective version of the LACASA-DA reaction. This objective was ultimately achieved by developing a novel heterobimetallic bifunctional catalyst with 1,1'-bi(2-naphthol) (BINOL) as the chiral non-racemic ligand.*.;*Please refer to dissertation for diagrams.