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Ring Expansion of Heterocyclic Ketene N,X ‐Acetals and 2‐Alkylidenedihydroindoles with Methanesulphonyl Azide by [3 + 2] Cycloaddition and Subsequent Extrusion of Molecular Nitrogen
Author(s) -
Quast Helmut,
Ivanova Svetlana,
Peters EvaMaria,
Peters Karl,
Schnering Hans Georg Von
Publication year - 1996
Publication title -
liebigs annalen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0947-3440
DOI - 10.1002/jlac.199619961008
Subject(s) - ketene , chemistry , ring (chemistry) , cycloaddition , nitrogen atom , azide , deprotonation , nitrogen , solvent , extrusion , molecule , stereochemistry , medicinal chemistry , crystallography , organic chemistry , catalysis , materials science , metallurgy , ion
Methanesulphonyl azide ( 2 ) reacts readily with isolated cyclic ketene N,X ‐acetals of type 1 , viz. 10a, d, 15b, d , and 22a–c , or those that are generated in situ by deprotonation of the corresponding 2‐alkylbenzazolium tetrafluoroborates, i.e. 14a → 15a, 14b → 15b , and 18 → 19 . Ring‐expanded products are formed by extrusion of molecular nitrogen from intermediate labile [3 + 2] cycloadducts 3 with concomitant 1,2‐shift of N (route A1 → 12, 24 ) or X (route A2 → 16, 20, 21 ). In addition, 3 may undergo [3 + 2] cycloreversion into N ‐sulphonylimine 5 and diazoalkane 6 (route B → 13, 17, 25 ). The configurations of the cyclic N ‐sulphonylamidines 16b and 21b , the N ‐sulphonylimine 24 and the N ‐sulphonylamine 27 are elucidated by means of X‐ray diffraction analyses. The ratio of the (useful) ring‐expansion reactions vs. the unwanted formation of 5 + 6 is hardly influenced by the solvent employed and temperature of the experiment but strongly by the nature of the potential migrating atom and the substituents at the α‐carbon atom.