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■ Interne Photocyclisierungen von Bi-1,2-dihydroisochinolinen und eines Methylen-bis-naphthalinones

Yushin Nakamura, Janos Zsindely, and Hans Schmid*

*Organisch-chemisches Institut, Universität, Rämistrasse 76, CH-8001 Zürich, Switzerland

Abstract

The bi-dihydro isoquinoline derivative rac-1 upon short triplet sensitized irradiation leads in high yield by an internal [2+2] cyclisation to product 3 (scheme 1). Reduction with di-isobutylaluminium hydride gives the bis-amine 4. Analogous irradiation of meso-1 gives the expected cyclisation product 5 only in moderate yield; the main product is again 3. Its formation must have been preceded by a photochemical meso-1 → rac-1 isomerization. The 3,3’-dimethyl derivates rac-2 and meso-2 undergo similar internal photocyclisations (scheme 1).
The structure of the above mentioned compounds was established by spectroscopic methods, especially ¹H-NMR-spectra. A cyclobutane derivative, namely 13, is also formed upon direct irradiation of the bisnaphthalene derivative 10. 10 is a component of the equilibrium mixture that is formed by heating the bis-allylether 11 to 160 °. The main components of this equilibrium mixture, however, are 11 and 12.