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Photochemical reactions. 152nd Communication. Photochemistry of acylsilanes; photolysis and thermolysis of cyclopropyl silyl ketones

✍ Scribed by Markus E. Scheller; Bruno Frei

Publisher
John Wiley and Sons
Year
1990
Tongue
German
Weight
587 KB
Volume
73
Category
Article
ISSN
0018-019X

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✦ Synopsis

Abstract

The photolysis and thermolysis of the Cyclopropyl silyl ketones 3, 4, and 5 are described. On n,π* excitation, the silyl ketones 3 and 4 undergo a Norrish‐type‐II reaction involving γ‐H abstraction, cyclopropyl ring cleavage followed by retro‐enolization to the acylsilanes 6 and (E/Z)‐12, respectively. As a common product of 3 and 4, the dihydrofuran 7 is formed via the alternative C(α)‐C(β) cleavage of the cyclopropyl moiety. Compounds 6, 7, and (E/Z)‐12 are new types of acylsilane photoproducts. The irradiation of acylsilane 5 gave the analogous dihydrofuran 15 as the only product. On photolysis of 3 and 4, products 8A + B and 13A + B, derived from a siloxy carbene intermediate, were found as well. On thermolysis of 3 and 4, the acylsilanes 6 (80%), and (E)‐12 (33%) and (Z)‐12 (34%), respectively, are formed as the only products. Their formation may occur via a [1, 5] sigmatropic H‐shift. The thermolysis of 5 gave the diene 16 whose formation can be explained by insertion of a siloxycarbene into the neighboring cyclopropane leading to the cyclobutene 28 as thermally unstable intermediate.

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