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Enantioselective intermolecular [2+2] photocycloadditions of isoquinolone mediated by a chiral hydrogen-bonding

Susannah C Coote1, Thorsten Bach

  • 1Lehrstuhl für Organische Chemie I and Catalysis Research Center, Technische Universität München , Lichtenbergstrasse 4, 85747 Garching, Germany.

Journal of the American Chemical Society
|October 2, 2013
PubMed

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Photochemical Electrocyclic Reactions: Stereochemistry

The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
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The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.