Titanium-mediated spirocyclization reactions of 4-alkylpyridines.
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(O(i)Pr)(4). Cyclization products could be easily converted into spiro-piperidine derivatives or elaborated into more complex heterocyclic frameworks via Au-catalyzed cycloisomerization.
Parameswarappa
Sharavathi G
SG
Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, USA.
Pigge
F Christopher
FC