Enantioselective Template‐Directed [2+2] Photocycloadditions of Isoquinolones: Scope,Mechanism and Synthetic Applications |
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Authors: | Dr Susannah C Coote Dr Alexander Pöthig Prof Dr Thorsten Bach |
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Institution: | 1. Department Chemie, Technische Universit?t München, Lichtenbergstrasse 4, 85747 Garching (Germany);2. Current address: Department of Chemistry, Lancaster University, Bailrigg, Lancaster, LA1 4YB (U.K.) |
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Abstract: | A strategy for the enantioselective 2+2] photocycloaddition of isoquinolones with alkenes is presented, in which the formation of a supramolecular complex between a chiral template and the substrate ensures high enantioface differentiation by shielding one face of the substrate. Fifteen different electron‐deficient alkenes and ten different substituted isoquinolones undergo efficient photocycloaddition, yielding the cyclobutane products in excellent yields and with outstanding regio‐, diastereo‐ and enantioselectivities (up to 99 % ee). The mechanism of the reaction is investigated by means of triplet sensitization/quenching and radical clock experiments, the results of which are consistent with the involvement of a triplet excited state and a 1,4‐biradical intermediate. The variety of functionalized cyclobutanes obtained using this approach can be further increased by straightforward synthetic transformations of the photoadducts, allowing rapid access to libraries of compounds for various applications. |
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Keywords: | asymmetric synthesis enantioselectivity hydrogen bonding photochemistry synthetic methods |
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