Competition between Inter- and Intramolecular Photocycloaddition Reactions of 9-Substituted Anthracenes

Abstract

A number of 9-[(arylmethoxy)methyl]anthracenes were prepared and their photoreactivity was studied. The intramolecular [4π+4π]cycloaddition competes with the intermolecular head-to-tail [4π+4π] cyclodimerization. The aryl substituents control the selectivity; concentration only plays a role in selectivity in certain cases. The complete reversibility of the cycloaddition makes this process suitable as a molecular switch, provided that traces of acids are avoided; when acid is present the cyclomers pursue an irreversible enol ether cleavage route.

Key words

cycloaddition - cyclodimerization - ether cleavage - regio­selectivity - retrocycloaddition

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9

Dimers in which the benzene rings and the anthracene units react mutually, were found for 9,10-disubstituted anthracenes¹⁰ and can be ruled out here under the reaction conditions used.

13

We attribute the quantitatively different concentration effects to different aggregation tendencies.

14

Commercially available.

15

The bromo compound 3k is thermolabile and light-sensitive, correct elemental analysis could not be obtained.