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Lewis Acid Catalyzed Enantioselective Photochemical Rearrangements on the Singlet Potential Energy Surface.

ABSTRACT: The oxadi-?-methane rearrangement of 2,4-cyclohexadienones to bicyclic ketones was found to proceed with high enantioselectivity (92-97% ee) in the presence of catalytic amounts of a chiral Lewis acid (15 examples, 52-80% yield). A notable feature of the transformation is the fact that it proceeds on the singlet hypersurface and that no triplet intermediates are involved. Rapid racemic background reactions were therefore avoided, and the catalyst loading could be kept low (10 mol %). Computational studies suggest that the enantioselectivity is determined within a Lewis acid bound singlet intermediate via a conical intersection. The utility of the method was demonstrated by a concise synthesis of the natural product trans-chrysanthemic acid.

SUBMITTER: Leverenz M

PROVIDER: S-EPMC6935867 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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Lewis Acid Catalyzed Enantioselective Photochemical Rearrangements on the Singlet Potential Energy Surface.

Leverenz Malte M Merten Christian C Dreuw Andreas A Bach Thorsten T

Journal of the American Chemical Society 20191216 51

The oxadi-π-methane rearrangement of 2,4-cyclohexadienones to bicyclic ketones was found to proceed with high enantioselectivity (92-97% <i>ee</i>) in the presence of catalytic amounts of a chiral Lewis acid (15 examples, 52-80% yield). A notable feature of the transformation is the fact that it proceeds on the singlet hypersurface and that no triplet intermediates are involved. Rapid racemic background reactions were therefore avoided, and the catalyst loading could be kept low (10 mol %). Comp ...[more]

PMID: 31814393

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