A Cu(I)-catalyzed coupling of a ω-chloro ketone, a primary amine, and an alkyne is described. This protocol allows for the synthesis of α-quaternary carbons in 2-alkynyl-substituted N-heterocycles. The key step is the in situ generation of a cyclic ketiminium species, which has enhanced reactivity for alkynylation compared to acyclic ketiminium species.

Calcium carbide was used in a Cu -catalysed three-component coupling with ω-chlorinated ketones and primary amines to generate terminal 2-alkynyl-N-heterocycles. The formation of an imine and the subsequent intramolecular substitution results in an active electrophilic iminium species, which can be alkynylated by in situ formed copper acetylide. A number of aliphatic primary (functionalised) amines and aliphatic or aromatic alkynes together with different alkyl- or aryl-substituted γ- or δ-chloroketones could be used. Simple acid-base workup instead of column chromatography can be applied to obtain the resulting 2-alkynylpyrrolidines and 2-alkynylpiperidines.

A new synthetic methodology for the functionalization of the dichloromethylene moiety in 3,3‐dichloropiperidines via Pd‐catalyzed cross‐coupling reactions is reported. A range of 3,3‐dichloropiperidines was synthesized via a hydride induced cyclization of α,α,δ‐trichloroaldimines or an indium(III) triflate catalyzed alkynylation/cyclization procedure of α,α,δ‐trichloroaldimines. Subsequently, a dehydrochlorination followed by a cross‐coupling with the thus formed vinylic chloride was envisioned. The non‐alkynylated 3,3‐dichloropiperidines could be regioselectively eliminated and by careful choice of solvent and base both of the two regioisomeric vinyl chlorides could be exclusively formed. Palladium‐catalyzed Suzuki cross‐coupling of the thus formed 5‐chloro‐1,2,3,6‐tetrahydropyridines led to C3‐substituted 1,2,3,6‐tetrahydropyridines, which could be easily reduced to 3‐substituted piperidines, generating therapeutic agent (±)‐Preclamol for example. The 2‐alkynyl‐3,3‐dichloropiperidines were regioselectively eliminated giving the cyclic enamine, which was subsequently cross‐coupled in one‐pot. The presence of the alkynyl function, in this case, clearly directs elimination towards enamine structures. Hydrogenation of the resulting, unstable 2‐alkynyl‐3‐substituted‐1,2,3,4‐tetrahydropyridines, yields stable 2,3‐disubstituted piperidines.

A one-pot, three-component, Cu(I)-catalyzed coupling of primary hydrazines, 5-chloropentan-2-one, and terminal alkynes was developed. The resulting 1-aza-6,7-dehydrotropanes compose a new class of substances while related 1-azatropanes are scarcely described in literature and closely resemble tropane alkaloids. Hydrogenation of the double bond in 1-aza-6,7-dehydrotropanes triggered a rearrangement, involving a [1,3]-hydride shift, forming cyclic hydrazones.