Synthesis of 1,6-methano[10]annulenopyridines by tandem aza-Wittig reaction/electrocyclisation

Abstract

Iminophosphoranes 1(X = PPh₃) derived from the corresponding 1,6-methano[10]annulenes have been made to react with isothiocyanates and also with aromatic aldehydes to give, by an aza-Wittig reaction followed by cyclisation, novel 1,6-methano[10]annulenopyridines of structural types 2 and 6. Aza-Wittig reactions of the 2-triphenylphosphoranylideneamino derivative 3(X = PPh₃) with aromatic aldehydes or isothiocyanates led to the Schiff's bases 3(X = CHAr) or carbodiimides (X = CNAr) respectively. The latter on treatment with enamines gave, by a Diels–Alder cyclisation, the annuleno[2,3-b]pyridines 12.