Titanium-Mediated Spirocyclization Reactions of 4-Alkylpyridines
摘要:
Pyridines substituted at the 4-position with alkyl tethers containing beta-dicarbonyl moieties were converted to spirocyclic 4,4-disubstituted dihydropyridines. Optimal conditions for these transformations involved N-acylation of the pyridine substrate with a chloroformate electrophile in the presence of Ti((OPr)-Pr-i)(4). Cyclization products could be easily converted into spiro-piperidine derivatives or elaborated into more complex heterocyclic frameworks via Au-catalyzed cycloisomerization.