Amidinium ring closure with

Ring closures with vinylogous amidinium salts O... 

Aminocrotonate ester or aminocrotonitriles are cyclocondensed with vinylogous amidinium salts or enaminone ketals to give pyridine-3-carboxylic acid derivatives via electrocyclic ring closure of an intermediate adduct68-70 (equation 50). 

Precursor 12 for a N-heterocyclic diaminocarbene possessing a six-mem-bered heterocycle was obtained from the reaction of a suitable 1,3-diamino-propane with triethyl orthoformiate (Scheme 1.7d). Related compounds with an aromatic backbone were obtained from diaminonaphthalene. While these methods are based on the ring closure by introduction of a CH" fragment, Bertrand and co-workers presented a dilferent approach based on the reaction of a 1,3-diazaallyl anion with compounds featuring two leaving groups. Amidinium salts with both six- or seven-membered heterocycles (12 or 13) were obtained by this method (Scheme 1.7e) which was further developed by Cavell ... 

---