Intramolecular Cyclization of Alkynylheteroaromatic Substrates Bearing a Tethered Cyano Group: A Strategy for Accessing Fused Pyridoheterocycles

Heterocyclic substrates containing a conjugated alkyne and a pendant nitrile were shown to cyclize in an overall tetradehydro-Diels-Alder reaction to give products in which the initial heterocycle bears a newly fused pyridine ring. Base-promoted tautomerization of the alkyne to its isomeric allene allows this process to occur at ambient temperature. DFT studies support many of the mechanistic interpretations of the overall results.