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15.1.1.1.7.3.5.1 Variation 1: From Functionalized Enamines and Alkynones (Bohlmann–Rahtz Synthesis)

DOI: 10.1055/sos-SD-015-00002

Spitzner, D.Science of Synthesis, (20051568.

Acyl-, acetyl-, or cyano-substituted enamines, e.g. 232, react exothermally with alkynones and the intermediate, formed by Michael addition of the enamine to the alkynone, ­cyclizes under thermal or acidic conditions to give pyridines, e.g. 233 and 234 (Scheme 78).[‌285‌‌288‌] Ytterbium(III) trifluoromethanesulfonate, zinc(II) bromide, and Amberlyst 15 ion-exchange resin are the most efficient Lewis acids which catalyze the BohlmannRahtz reaction to generate highly functionalized pyridines, e.g. 235, from enamino ­esters, e.g. 84, and al­kynones in one pot.[‌289‌,‌290‌]

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