| Popis: |
Aza Wittig reaction of iminophosphoranes derived from ethyl α-azido-β-aryl(pyrazolyl)propenoates with α,β-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 α-azido-β-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). |
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