Pyridine Ring Heterannulation via Imine-eneyne Ring Closure

Significance

Reported is a synthesis of ring-annulated pyridines from iodine-induced cyclization of azadienyne intermediates. The lithio enyne, generated by metal-halogen exchange or deprotonation with t-BuLi, undergoes reaction with p-TolCN to give the conjugated imine which, by treatment with iodine undergoes an overall 6-endo-dig ring closure to give the substituted pyridine. The eneynic systems may be obtained through the use of a copper alkyne coupling methodology as shown.