Transition-Metal-Free Superbase-Catalyzed C–H Vinylation of Aldimines with Acetylenes to 1-Azadienes

Abstract

Aldimines react with aryl- and hetarylacetylenes in the presence of KOBu t /dimethyl sulfoxide (DMSO) or NaOBu t /DMSO systems under exceptionally mild conditions (14 °C, 1 h) to afford C–H-vinylated products, 1-azadienes of E configuration relative to the C–C bond, in up to 72% yield. Vinylation involves the unprecedentedly fast multiposition proton transfer in the intermediate adducts of acetylene to the CN bond. This new Csp2–Csp2 bond-forming reaction opens a straightforward pot-, atom-, step-, and energy-economic access to synthetically valuable 1-azadienes.

Quantum-Chemical Study of the Assembly Mechanism of 1-Pyrrolines from N-Benzylaldimines and Arylacetylenes in KOtBu/DMSO Superbasic Medium

“…Experimental studies of the interaction of imines with acetylenes in superbasic media such as MO t Bu/dimethyl sulfoxide (DMSO) (M = Na and K) have led to the discovery of a number of new reactions for the formation of C–C and C–N bonds. These are, in particular, the reactions of (i) ethynylation of N -arylketimines by acetylenes yielding propargylamines, (ii) α-C–H vinylation of N -benzylketimines by acetylene leading to 2-azadienes, and (iii) formal CH-vinylation of arylaldimines with arylacetylenes yielding 1-azadienes . Noteworthy, we have shown that ethynylation reactions of N -phenylacetaldimine and 2-pyridylphenylimine are the key steps of the assemblies of both N -phenyl-2,5-dimethylpyrroles , and ( Z )-stilbene- and benzylimidazopyridines…”

A Highly Stereoselective Redox Isomerization-Reductive Deuteration Sequence of Propargyl Amines to α-Deuterated Amino Acids

“…Ben-Efraim et al discovered that t -BuOK effectively mediates the isomerization of secondary propargylic amines to α,β-unsaturated imines . Subsequently, several studies on t -BuOK catalyzed redox isomerization have been reported . These base-catalyzed processes likely proceed through allenylamine intermediates, ultimately yielding thermodynamically stable E -configured α,β-unsaturated imines as the final product.…”

“…Although significant progress has been made in the redox isomerization of propargylic amines, ,, the corresponding transformation of α-alkynyl amino acid derivatives remains unexplored. Therefore, we initially evaluated the redox isomerization of α-phenylethynyl ethyl glycinate 1a (Table ).…”

Base-Catalyzed [3 + 2] Cycloaddition ofN-Benzyl Ketimines to Arylacetylenes Followed by Oxidation: A One-Pot Access to Polyarylated 2H-Pyrroles via Intermediate Pyrrolines

“…Earlier, we have reported that ketimines in the same superbasic medium are added to arylacetylenes as C sp -centered carbanions to deliver propargylamines (Scheme B). Arylaldimines under similar conditions are formally CH-vinylated with arylacetylenes to 1,2,4-triaryl-1-azabutadienes (Scheme C) …”

“…If, according to ref , the reaction starts with the addition of acetylide anions to the C=N bond, then another regioisomeric pyrroline (with R 4 in the position 4) would be formed.…”