Synthesis 2001(8): 1236-1242
DOI: 10.1055/s-2001-15076
PAPER
© Georg Thieme Verlag Stuttgart · New York

Intramolecular [2+2] Photocycloaddition of Bichromophoric Derivatives of 3,5-Dihydroxybenzoic Acid and 3,5-Dihydroxybenzonitrile

Norbert Hoffmann*, Jean-Pierre Pete
Laboratoire des Réactions Sélectives et Applications, UMR CNRS et Université de Reims Champagne-Ardenne, UFR Sciences, B.P. 1039, 51687 REIMS, cedex 2, France
Fax: +33(0)326913166; e-Mail: norbert.hoffmann@univ-reims.fr;
Further Information

Publication History

Received 18 December 2000
Publication Date:
24 September 2004 (online)

Abstract

The irradiation of 3-alkenyloxy-5-hydroxybenzoic acid derivatives 1a-d yields highly functionalized alkyloxyenone derivatives when the reaction is carried out in the presence of acid. A higher reactivity is observed for the corresponding 3-alkenyloxy-5-hydroxybenzonitrile compounds 7a, b, which also react in neutral reaction media. In the first step of the reaction, a [2+2] photocycloaddition occurs. The following steps, leading to stable final products, need acid catalysis in the case of the substrates 1a-d. The irradiation of the benzonitrile derivative 7b also furnishes the side product 9, which results from a [2+3] photocycloaddition.

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When 7b was irradiated at λ = 300 nm in acetone, a decrease of the conversion rate and the amount of 8b was observed. No formation of compound 9 could be detected. In contrast, when the reaction of 7a was carried out in the presence of 1,3-cyclohexadiene (1.5 m/L, ET = 52.4 kcal/mol; (Murov, S. L. Handbook of Photochemistry; Marcel Dekker: New York, 1973) in acetonitrile-toluene (1:1), the formation of 8a was not affected. These results led us to conclude that the formation of the products 8a and 8b results from a transformation of 7a or 7b in their singlet excited state.