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Photochemistry of 3‐Substituted 1‐Iminopyridinium Ylides . Regiospecific versus non‐regiospecific photoisomerization patterns [1]
Author(s) -
Fritz Hans,
Gleiter Rolf,
Nastasi Michel,
Schuppiser JeanLuc,
Streith Jacques
Publication year - 1978
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19780610815
Subject(s) - chemistry , isomerization , photoisomerization , ring (chemistry) , halogen , photochemistry , medicinal chemistry , stereochemistry , organic chemistry , catalysis , alkyl
Abstract 3‐Substituted 1‐iminopyridinium ylides 1 undergo photo‐induced ring enlargement to 1 H ‐1,2‐diazepines. With strongly electron‐withdrawing substituents the ring expansion process is regiospecific and leads exclusively to 4‐substituted 1 H ‐1, 2‐diazepines. Weak electron‐donating substituents, like a methyl group and halogen atoms, do not have any directing effect since both 4‐ and 6‐substituted 1 H ‐1,2‐diazepines are obtained. With strong electron‐donating substituents no diazepines are formed; instead one observes photo‐induced isomerization to the 2‐aminopyridine derivatives, the process being non‐regiospecific. Regiospecific photo‐induced ring expansion processes are explained in terms of a simple HMO model.