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Mechanistic Investigation of the Ring Opening in the Staudinger Cycloaddition Involving Ketenes with Electron‐Withdrawing Substituents
Author(s) -
Mo Shanyan,
Xu Jiaxi
Publication year - 2012
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.201100483
Subject(s) - chemistry , cycloaddition , isomerization , ring (chemistry) , polar effect , staudinger reaction , medicinal chemistry , stereochemistry , photochemistry , organic chemistry , catalysis
The cycloaddition of ketenes and imines ( Staudinger cycloaddition) is a general method for the synthesis of various β ‐lactams. However, reactions of imines and ketenes with electron‐withdrawing substituents produce α , β ‐unsaturated alkenamides, ring‐opening products of the intermediates generated from imines and the ketenes, even as sole products, besides the desired β ‐lactams. The mechanism of the formation of α , β ‐unsaturated alkenamides was investigated. The results indicate that the α , β ‐unsaturated alkenamides are generated via a base‐induced CC bond isomerization followed by electrocyclic ring opening of the formed azacyclobutenes (=1,2‐dihydroazetes; cf. Scheme 3 ).