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4‐Substituted 2,3‐Dihydroisoxazoles as Masked Azomethine Ylides: Access to Pyrrole Derivatives by 1,5‐ and 1,7‐Dipolar Electrocyclizations of Enynyl Derivatives
Author(s) -
Friebolin Wolfgang,
Eberbach Wolfgang
Publication year - 2001
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 - 10.1002/1522-2675(20011219)84:12<3822::aid-hlca3822>3.0.co;2-o
Subject(s) - chemistry , alkyne , pyrrole , medicinal chemistry , conjugated system , thermal decomposition , combinatorial chemistry , ring (chemistry) , bicyclic molecule , catalysis , organic chemistry , polymer
The enynyl‐substituted 2,3‐dihydroisoxazoles (‘isoxazolines') 9 – 14 were prepared by highly ( Z )‐selective Peterson olefination reaction from the corresponding carbaldehydes 6 – 8 . On short‐time thermolysis (280 – 406°/10 s) the TMS derivatives 9 – 11 give rise to the annulated pyrrolines 18 – 20 , which, in some cases, suffer CH 4 elimination affording the pyrroles 15 – 17 . In contrast, thermolysis of the terminal alkyne derivatives 12 – 14 leads to the bicyclic compounds 21 – 23 . The reaction pathways are discussed on the basis of the formation of conjugated azomethine ylides as key intermediates, which either undergo a 1,5‐cyclization to 18 – 20 or a 1,7‐ring‐closure affording cycloallene intermediates of type V , which are further transformed into the azepino pyrroles 21 – 23 .