Fused mesoionic heterocycles: synthesis of 1,3,4-oxadiazolo[3,2-a]pyridine and 1,3,4-thiadiazolo[3,2-a]pyridine derivatives
- 1 January 1982
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 1
- p. 351-355
- https://doi.org/10.1039/p19820000351
Abstract
Two general methods are reported for the preparation of mesoionic derivatives of 1,3,4-oxadiazolo[3,2-a] pyridine and 1,3,4-thiadiazolo[3,2-a]pyridine from 1-amino-4,6-diphenyl-2-pyridone (3) and 1-amino-4,6-diphenylpyridine-2-thione (4), respectively. The first involves the initial formation of N,N′-disubstituted ureas or thioureas (7)–(11), which undergo cyclization either by thermal treatment [to give (14) and (15)] or by the action of Ph3P–CCl4[to give (16)–(20)]. The second is based in the reaction of the iminophosphoranes (12) and (13) with carbon dioxide or carbon disulphide and isocyanates or isothiocyanates to give 2-olates [(14) and (15)], 2-thiolates [(21) and (22)], or 2-aminides [(16)-(20)]. The reactions of the N-amino-heterocycle (4) with phenyl isothiocyanate and ethoxycarbonyl isothiocyanate led directly to the mesoionic compounds (19) and (20), respectively.Keywords
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