Reaction of α,β‐unsaturated carbodiimides with enamines leading to fused pyridine derivatives

Abstract

The treatment of (5,5‐dimethyl‐3‐oxo‐1‐cyclohexenyl)iminotriphenylphosphorane (2) with phenyl isocyanate (3a) gave N‐(5,5‐dimethyl‐3‐oxo‐1‐cyclohexenyl)‐N'‐phenylcarbodiimide (4a) in situ. The reaction of 4a with enamines proceeded smoothly to afford the pyridine ring formation with the elimination of amine. This means that 4a is regarded as a new class of 2‐aza‐1,3‐butadiene. The scopes and limitation of this reaction are also discussed.

Chichibabin-Type Condensation of Cyclic Ketones with 3-R-1,2,4-triazin-5(4H)-ones

“…The reaction requires high pressure , or hydrothermal conditions in aqueous ammonium chloride . Procedures that utilize activated forms of cyclic ketones, such as the product of dimerization of cyclohexanone-1,1′-bi(cyclohexilidene)-2-one, enamines of cyclic ketones, , are noteworthy. Syntheses from pyrylium salts and cyclobutadienes are also known.…”