Synlett 2003(4): 0451-0472
DOI: 10.1055/s-2003-37505
ACCOUNT
© Georg Thieme Verlag Stuttgart · New York

Spin-Selectivity in Photochemistry: A Tool for Organic Synthesis

Axel G. Griesbeck*
University of Cologne, Institute of Organic Chemistry, Greinstr. 4, 50939 Köln, Germany
Fax: +49(221)4705057; e-Mail: griesbeck@uni-koeln.de;
Further Information

Publication History

Received 17 May 2002
Publication Date:
26 February 2003 (online)

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Abstract

The photochemistry of carbonyl substrates is largely dependent on the spin multiplicity of the excited state. Singlet and triplet excited carbonyls can differ strongly in chemo-, regio- and stereoselectivity. In bimolecular Paternò-Büchi reactions, both excited singlet and triplets states give rise to oxetane formation, albeit with different selectivities and completely different activation parameters. In unimolecular photocyclizations (Norrish-Yang reaction) the triplet state dominates the reaction. For triplet to singlet intersystem crossing at the biradical level, spin-orbit coupling optimizing geometries are crucial. These geometries are different from classical closed-shell interactions and thus give rise to unusual product stereochemistry as well as unusual concentration and temperature dependences.

  • 1 Introduction

  • 2 The Carbonyl-Ene Photocycloaddition

  • 2.1 First Surprises

  • 2.2. First Concepts

  • 2.3 Further Surprises

  • 2.4 Further Concepts and Examples

  • 2.5 Concentration and Temperature Studies

  • 3 The Enone-Ene Photocycloaddition

  • 4 The Norrish-Yang Photocyclization

  • 4.1 The Classical Version

  • 4.2 Extended Versions

  • 4.3 Chirality Transfer and Memory of Chirality

  • 5 Where to go?