6π-electrocyclization of azahexa-1,3,5-trienes: a new entry to a regiospecific synthesis of 3-aryl(heteroaryl)pyridines
作者:Pedro Molina、Aurelia Pastor、Maria Jesús Vilaplana
DOI:10.1016/s0040-4020(01)87250-1
日期:1993.8
Aza Wittig reaction of iminophosphoranes derived from ethyl alpha-azido-beta-aryl(pyrazolyl)propenoates with alpha,beta-unsaturated aldehydes leads to aldimines which by heating undergo electrocyclic ring-closure through the 3-azahexa-1,3,5-triene moiety to give 3-aryl(pyrazolyl)pyridines in a completely regiospecific fashion. However, iminophosphoranes derived from ethyl alpha-azido-beta-furyl(thienyl)propenoates furnish a mixture (1.2:1 ratio) of the corresponding furo- or thieno-pyridine(2-azahexa-1,3,5-triene electrocyclization product) and 3-furyl(thienyl)pyridine(3-azahexa-1,3,5-triene electrocyclization product).