Synthesis of Indolizines and Heterocyclic Chalcones Catalyzed by Supported Copper Nanoparticles

Abstract

Solvent decides: Versatile copper nanoparticles (Cu NPs) on activated carbon have been found to catalyze the multicomponent synthesis of indolizines in dichloromethane and the synthesis of heterocyclic chalcones in the absence of solvent, in both cases, from pyridine-2-carbaldehyde derivatives, secondary amines, and terminal alkynes (see scheme).

Synthetic and Mechanistic Studies on the Solvent-Dependent Copper-Catalyzed Formation of Indolizines and Chalcones

“…24 With the optimized conditions in hand, a wide range of indolizines were synthesized in modest-to-high isolated yields by using low catalyst loading (0.5 mol%) ( Table 1). Pyridine-2-carbaldehyde (1a) was successfully combined with six different secondary amines (2a-f) and seven aryl acetylenes containing electron-neutral, -withdrawing or -releasing substituents (3a-g).…”

“…Owing to our interest in metal colloids 22 and the application of supported copper nanoparticles (CuNPs) in organic chemistry, 23 we have recently communicated the multicomponent synthesis of indolizines from pyridine-2-carbaldehyde derivatives, secondary amines and terminal alkynes catalyzed by copper nanoparticles on activated carbon in dichloromethane (Scheme 2). 24 Interestingly, the same starting materials (with piperidine as the secondary amine) and catalyst used for this purpose gave rise to heterocyclic chalcones in the absence of solvent, with this representing the first copper-catalyzed synthesis of chalcones (without rearrangement) from aromatic aldehydes and alkynes. We wish to present herein a complete study which includes the scope of this methodology, more focused on the synthesis of chalcones and, most importantly, our endeavour to understand mechanistically the formation of both the indolizines and chalcones.…”

Gold(I)‐Catalyzed Diastereoselective Hydroacylation of Terminal Alkynes with Glyoxals

“…To gain further insight, the a-deuterated phenylglyoxal was prepared by oxidation of deuterated phenylacetylene. [2] Its conversion under standard conditions showed no deuterium incorporation into the final product, which excludes a 1,3-hydrogen shift [8] as an elementary step of the reaction mechanism. Our next labeling experiment was conducted with D 2 O as a deuterium source and product 5 a' was obtained.…”

One‐Pot Alkynylation of Azaaryl Aldehydes and Spontaneous Base‐Free Rearrangement into Enone Esters: an Autoinductive Mechanism

“…[29][30][31][32][33] All these methods require first forming and isolating the propargylic alcohol and then submitting it to the rearrangement conditions. [35,36] We have recently reported on the use of the Soai's autocatalyst in the asymmetric alkynylation of azaaryl aldehydes with various zinc acetylinides. [34] The reaction was promoted by KOtBu and provided a rapid access to (E)-1-en-4-yn-3-ol and (Z)-2-en-4-yn-1-ol compounds.…”