One pot synthesis of nitrogen-containing polycyclic δ-lactones by double nucleophilic addition of bis(trimethylsilyl)ketene acetals to pyridinesAll new compounds described in this paper were fully characterized by 200 and 400 MHz 1H NMR, 50 or 100 MHz 13C NMR, mass spectrometry and/or elemental analyses.
Pyridine and bis(TMS)ketene acetals (TMS = trimethylsilyl) react successively with methylchloroformate and iodine (or peracids) to give, via functionalized dihydropyridines, bicyclic nitrogen-containing lactones which have been characterized by X-ray crystallography.
Whereas for 3-fluorodihydropyridine-substituted carboxylic acids electrophiles such as HCl, iodine, bromine and peracids discriminate the double bond lacking and that bearing fluorine, no such differentiation took place in the case of electrophilic fluorine since the formation of both mono and gem-difluorolactones took place.