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.