Practical synthesis and mechanistic study of polysubstituted tetrahydropyrimidines with use of domino multicomponent reactions

New frontiers in the transition-metal-free synthesis of heterocycles from alkynoates: an overview and current status

This review highlights the successful utilization of transition-metal-free approaches for the modular assembly of various heterocycles from alkynoates.

Water–DMSO-promoted one-pot synthesis of two new series of dihydropyrrolo[2,3-h]quinolines

Two new series of dihydropyrrolo[2,3-h]quinolines 4 and 6 were synthesized via a three-component reaction synergistically activated by water and DMSO, and new pyrrolo[2,3-h]quinolines 10 can be obtained by oxidation of 4 using Cu(NO₃)₂ as oxidant.

4-Aminoindoles as 1,4-bisnucleophiles for diversity-oriented synthesis of tricyclic indoles bearing 3,4-fused seven-membered rings

A straightforward access to tricyclic indoles bearing 3,4-fused seven-membered rings was established by using 4-aminoindoles as 1,4-bisnucleophiles in three-component reactions.

Ultrafast and efficient aza- and thiol-Michael reactions on a polyester scaffold with internal electron deficient triple bonds

A polyester scaffold possessing electron deficient triple bonds in the main chain was prepared and utilized as a precursor for aza- and thiol-Michael addition reactions.

Metal-Free Multicomponent Tandem Polymerizations of Alkynes, Amines, and Formaldehyde toward Structure- and Sequence-Controlled Luminescent Polyheterocycles

Sequence-controlled polymers, including biopolymers such as DNA, RNA, and proteins, have attracted much attention recently because of their sequence-dependent functionalities. The development of an efficient synthetic approach for non-natural sequence-controlled polymers is hence of great importance. Multicomponent polymerizations (MCPs) as a powerful and popular synthetic approach for functional polymers with great structural diversity have been demonstrated to be a promising tool for the synthesis of sequence-controlled polymers. In this work, we developed a facile metal-free one-pot multicomponent tandem polymerization (MCTP) of activated internal alkynes, aromatic diamines, and formaldehyde to successfully synthesize structural-regulated and sequence-controlled polyheterocycles with high molecular weights (up to 69 800 g/mol) in high yields (up to 99%). Through such MCTP, polymers with the in situ generated multisubstituted tetrahydropyrimidines or dihydropyrrolones in the backbone and inherent luminescence can be easily obtained with high atom economy and environmental benefit, which is inaccessible by other synthetic approaches.

Efficient Synthesis of a Series of Novel Octahydroquinazoline-5-ones via a Simple on-Water Urea-Catalyzed Chemoselective Five-Component Reaction

Multicomponent reactions (MCRs) have become a powerful tool for drug discovery and development owing to their advantages of fast and efficient construction of a large library of products with complexity and diversity. However, conventional MCRs usually proceed in environmentally unfriendly organic solvents rather than in water, a green solvent used by nature for biological chemistry. Herein, a simple and efficient on-water urea-catalyzed chemoselective five-component reaction (5CR) has been developed for the synthesis of a series of novel octahydroquinazoline-5-ones (6), the derivatives of quinazolinones possessing diverse biological activities. The molecular structure of 6{1,1,12} has been confirmed by single-crystal X-ray diffraction. The 5CR can proceed at room temperature under normal atmospheric pressure in good yields and afford a large library of octahydroquinazoline-5-ones with various aromatic and aliphatic substituents at N-1, C-2, and N-3. In addition, a green method has been developed for the synthesis of enaminones, important intermediates in the 5CR and in synthetic chemistry.

Nano-MoO3 as a Highly Efficient Heterogeneous Catalyst for a One-Pot Synthesis of Tetrahydropyrimidine Derivatives in Water

A green and highly efficient one-pot synthesis of 16 1,3,4,5-tetrasubstituted 1,2,3,6-tetrahydropyrimidines, four of which are new, using a three-component reaction involving an aniline, formaldehyde and a dialkyl acetylenedicarboxylate in aqueous media at room temperature catalysed by nano-MoO3 has been achieved.

Synthesis of tetrahydropyrimidin-2-ones via FeCl3 catalyzed one-pot domino reaction of amines, methyl propiolate, aromatic aldehydes, and urea

Polysubstituted 3-arylaminoacrylate and tetrahydropyrimidin-2-one derivatives could be selectively produced from the one-pot domino reaction of arylamines, methyl propiolate, aromatic aldehydes, and urea in ethanol in the presence of FeCl3 as catalyst. Under similar reactions secondary amines such as morpholine and piperidine predominately afford tetrahydropyrimidin-2-one derivatives in good yields.

Base-promoted annulation of α-hydroxy ketones and dimethyl but-2-ynedioate: straightforward access to pyrano[4,3-a]quinolizine-1,4,6(2H)-triones and 2H-pyran-2,5(6H)-diones

A novel direct synthesis of pyrano[4,3-a]quinolizine-1,4,6(2H)-triones and 2H-pyran-2,5(6H)-diones from α-hydroxy ketones and dimethyl but-2-ynedioate via a base-promoted cascade annulation has been developed.

Development of four-component synthesis of tetra- and pentasubstituted polyfunctional dihydropyrroles: free permutation and combination of aromatic and aliphatic amines

We previously reported the novel efficient proton/heat-promoted four-component reactions (4CRs) of but-2-ynedioates, two same/different primary amines, and aldehydes for the synthesis of tetra- and pentasubstituted polyfunctional dihydropyrroles. If aromatic and aliphatic amines were used as reagents, four different series of products should be obtained via the permutation and combination of aromatic and aliphatic primary amines. However, only three/two rather four different series of tetra-/pentasubstisuted dihydropyrroles could be prepared via the proton/heat-promoted 4CRs. Herein, Cu(OAc)2·H2O, a Lewis acid being stable in air and water, was found to be an efficient catalyst for the 4CR synthesis of all the four different series of tetra-/pentasubstisuted dihydropyrroles. The copper-catalyzed 4CR could produce target products at room temperature in good to excellent yields. Interestingly, benzaldehyde, in addition to being used as a useful reactant for the synthesis of pentasubstituted dihydropyrroles, was found to be an excellent additive for preventing the oxidation of aromatic amines with copper(II) and ensuring the sooth conduct of the 4CRs for the synthesis of tetrasubstituted dihydropyrroles with aryl R(3). In addition, salicylic acid was found to be needed to increase the activities and yields of the copper-catalyzed 4CRs for the synthesis of petasubstituted diyhydropyrroles. On the basis of experimental results, the enamination/amidation/intramolecular cyclization mechanism was proposed and amidation is expected to be the rate-limited step in the copper-catalyzed 4CRs.

A novel class of small-molecule caspase-3 inhibitors prepared by multicomponent reactions

A series of tetra- and pentasubstituted polyfunctional dihydropyrroles 5 and 6 were synthesized via practical multicomponent reactions (MCRs) for research on their structure-activity relationship as caspase-3 inhibitors. Among 39 compounds evaluated, 14 of them exhibited inhibition against caspase-3 with IC(50) ranging from 5 to 20 μM. The inhibitory activities of 5 and 6 depend on the nature of substituents on different positions. 5 and 6 possess a different scaffold from those previously reported and are the first caspase-3 inhibitors prepared via MCRs. The most active compounds 5k (IC(50) = 5.27 μM) could therefore be used as a lead for the development of highly potent caspase-3 inhibitors as drug candidates for therapeutic agents by taking advantage of MCRs.

Synthesis of heterocyclic [3.3.3]propellanes via a sequential four-component reaction

A highly chemoselective heteroannulation protocol for the synthesis of unreported polysubstituted heterocyclic [3.3.3]propellanes has been developed by sequential four-component reaction of ninhydrin, malononitrile, primary amines, and dialkyl acetylenedicarboxylates under mild conditions in water. To the best of our knowledge, there are no previous reports for the synthesis of these classes of heterocyclic [3.3.3]propellanes. The merit of this sequential Knoevenagel condensation/enamine formation/Michael addition/cyclization sequence is highlighted by its high atom-economy, excellent yields, the use of water as reaction media, and the efficiency of production without the use of any activator or metal promoters. This synthesis serves as a nice addition to group-assistant-purification (GAP) chemistry in which purification via chromatography and recrystallization can be avoided, and the pure products were obtained simply by washing the crude products with 95% ethanol.

Synthesis of 3,4-dihydropyridin-2(1H)-ones and 3,4-dihydro-2H-pyrans via Four-component reactions of aromatic aldehydes, cyclic 1,3-carbonyls, arylamines, and dimethyl acetylenedicarboxylate

A protocol has been developed for the efficient synthesis of structurally diverse 3,4-dihydropyridin-2(1H)-ones and 3,4-dihydro-2H-pyrans via four-component reactions of arylamines, acetylenedicarboxylate, aromatic aldehydes and cyclic 1,3-diketones. The selective formation of the very different pyridinone or pyran derivatives depends on the structure of cyclic 1,3-diketone. The key steps are proposed to involve Michael addition of the enamino ester formed in situ from the reaction of arylamine with dimethyl acetylenedicarboxylate to arylidine cyclic 1,3-diketones.

Concise and versatile multicomponent synthesis of multisubstituted polyfunctional dihydropyrroles

Tetra- and pentasubstituted polyfunctional dihydropyrroles have been concisely synthesized in high yields by two different processes of the one-pot multicomponent reactions (MCRs) of but-2-ynedioates 1, amines 2, and aldehydes 3 at room temperature or at 70 degrees C. The first one involves a domino hydroamination/nucleophilic addition/amidation-cyclization process and leads to the formation of tetrasubstituted polyfunctional dihydropyrroles 4. The second undergoes hydroamination/amidation/intramolecular cyclization/imine-enamine tautomerization sequence and results in pentasubstituted products 5. The structures of 4 and 5 were confirmed by single-crystal X-ray diffraction. These novel methodologies provide easy access to diversely multisubstituted polyfunctional dihydropyrrole libraries. The primary biological screening in vitro against HIV-1 has shown that 22 tested compounds have exhibited significant activity with IC(50) in micromolar range (38-58 microM).