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Stereo- and spinselectivity of primary (singlet) and secondary (triplet) Norrish type II reactions

โœ Scribed by Axel G. Griesbeck; Andreas Henz; Wolfgang Kramer; Peter Wamser; Karl Peters; Eva-Maria Peters

Book ID
104258834
Publisher
Elsevier Science
Year
1998
Tongue
French
Weight
205 KB
Volume
39
Category
Article
ISSN
0040-4039

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โœฆ Synopsis

The influence of reactive conformation and substitution pattern on the Norrish Type II reactivity and selectivity of singlet-excited phthalimides was investigated. Only the cis-diasteroisomer of the 4-tert.-butyl cyclohexylamine derivatives 1 underwent Yang cyclization. The phthaloyl leucine esters 3a and 3b both gave primarily Yang cyclization with subsequent ring expansion. As a secondary photoreaction, 3a gave Norrish II cleavage solely, wheras photolysis of the tert.-butyl ester 3b resulted in a I: 1 mixture of Norrish II cleavage and Yang cyclization product 4 and 5.

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E&r since It was disrxvemd that both slrglet, and triplet states of allphatic ketones participate in Type II photoeliminat.icn processes (11, there has been speculation abmt the relative reactlvlties of the two excited states. In the cwl&lal report of polar solvent effects on photoelimination (2), o