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Reactions with diazoazoles. Part VI. Unequivocal synthesis of 3‐methyl‐3 h ‐azolotetrazoles. Correction of the formerly described 3‐methylazolotetrazoles in favour of mesoionic 2‐methylazolotetrazoles
Author(s) -
Ege Günter,
Heck Reinhard,
Gilbert Karlheinz,
Irngartinger Hermann,
HuberPatz Ursula,
Rodewald Hans
Publication year - 1983
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570200640
Subject(s) - mesoionic , chemistry , tetrazole , moiety , substituent , sodium ethoxide , medicinal chemistry , stereochemistry , annulation , thiazine , organic chemistry , ethanol , catalysis
3‐Methyl‐3 H ‐pyrazolo[1,5‐ d ]tetrazoles 2 and 3‐methyl‐6‐phenyl‐3 H ‐1,2,4‐triazolo[1,5‐ d ]tetrazole (4) have been unequivocally synthesized by annulation of the tetrazole moiety to the pyrazole resp. 1,2,4‐triazole system. The constitution of some N ‐methyl substituted azolotetrazoles, formerly described as 3‐methyl‐3 H ‐pyrazolo[1,5‐ d ]tetrazoles 2, 3‐methyl‐6‐phenyl‐3 H ‐1,2,4‐triazolo[1,5‐ d ]tetrazole (4) and 1‐methyl‐6‐phenyl‐1 H ‐1,2,4‐triazolo[4,3‐ d ]tetrazole (5), has to be revised in favour of the corresponding mesoionic 2‐methyl derivatives 2′, 4′, 5′. The structures of 3‐methyl‐3 H ‐ as well as of 2‐methyl‐2 H ‐pyrazolo[1,5‐ d ]tetrazole derivatives 2a, 2c, 2′a have been determined by X‐ray analyses. The azapentalenic system is aromatic in all three measured compounds and mesoionic in the case of the 2‐methyl‐2 H ‐ substitution pattern. The phenyl and ester substituents are coplanar with the azapentalene system. 3‐, 2‐, and 1‐Methylpyrazolo[1,5‐ d ]tetrazoles exhibit different behaviour when allowed to react with stannous chloride or sodium ethoxide. Azolotetrazoles with a methyl substituent at N‐1, N‐2 or N‐3 of the tetrazole moiety can be distinguished by a combination of 1 H and 13 C nmr with respect to the chemical shifts of the N ‐methyl group and the bridgehead carbon. Results of semiempirical calculations of the pyrazolo[1,5‐ d ]tetrazole anion and of its N ‐methyl derivatives are discussed.