Heteroring-Annulated Pyrrolino-Tetrahydroberberine Analogues

Diaza-1,3-butadienes as Useful Intermediate in Heterocycles Synthesis

Many heterocyclic compounds can be synthetized using diaza-1,3-butadienes (DADs) as key structural precursors. Isolated and in situ diaza-1,3-butadienes, produced from their respective precursors (typically imines and hydrazones) under a variety of conditions, can both react with a wide range of substrates in many kinds of reactions. Most of these reactions discussed here include nucleophilic additions, Michael-type reactions, cycloadditions, Diels–Alder, inverse electron demand Diels–Alder, and aza-Diels–Alder reactions. This review focuses on the reports during the last 10 years employing 1,2-diaza-, 1,3-diaza-, 2,3-diaza-, and 1,4-diaza-1,3-butadienes as intermediates to synthesize heterocycles such as indole, pyrazole, 1,2,3-triazole, imidazoline, pyrimidinone, pyrazoline, -lactam, and imidazolidine, among others. Fused heterocycles, such as quinazoline, isoquinoline, and dihydroquinoxaline derivatives, are also included in the review.

Application of 3-Alkyl-2-vinylindoles in Catalytic Asymmetric Dearomative (2+3) Cycloadditions

The first application of 3-alkyl-2-vinylindoles in catalytic asymmetric dearomative cycloadditions was established by chiral phosphoric acid (CPA)-catalyzed (2+3) cycloaddition with azoalkenes, leading to the generation of chiral pyrroloindolines bearing two tetrasubstituted stereogenic centers in good yields (61-96%) and excellent stereoselectivities (all >95:5 dr, 86-99% ee). This reaction has realized the first enantioselective dearomative cycloaddition of 3-alkyl-2-vinylindoles, which brings a new reactivity to this class of vinylindoles and will enrich the chemistry of 3-alkyl-2-vinylindoles. In addition, this approach has provided a useful strategy for the construction of enantioenriched pyrroloindoline skeletons bearing two tetrasubstituted stereogenic centers. More importantly, the bioassay of these chiral pyrroloindolines has revealed that some compounds exhibit strong anti-cancer activity against Hela and MCF-7 cell lines, which will be helpful for discovering anti-cancer drug candidates.

Synthesis of new dihydroberberine and tetrahydroberberine analogues and evaluation of their antiproliferative activity on NCI-H1975 cells

Dihydroberberine (DHBER), the partially reduced form of the alkaloid berberine (BER), is known to exhibit important biological activities. Despite this fact, there have been only few studies that concern the biological properties of functionalized DHBER. Attracted by the potentiality of this latter compound, we have realized the preparation of new arylhydrazono-functionalized DHBERs, starting from BER and some α-bromohydrazones. On the other hand, also the fully reduced form of BER, namely tetrahydroberberine (THBER), and its derivatives have proven to present different biological activities. Therefore, the obtained arylhydrazono-functionalized DHBERs were reduced to the corresponding arylhydrazono-THBERs. The antiproliferative activity of both arylhydrazono-DHBERs and -THBERs has been evaluated on NCI-H1975 lung cancer cells.

Catalytic Asymmetric Formal [3+2] Cycloaddition of Azoalkenes with 3-Vinylindoles: Synthesis of 2,3-Dihydropyrroles

Chiral phosphoric acid-catalyzed highly enantioselective formal [3 + 2] cycloaddition reaction of azoalkenes with 3-vinylindoles has been established. Under mild conditions, the projected cycloaddition proceeded smoothly, affording a variety of 2,3-dihydropyrroles in high yields and excellent enantioselectivities, and also in a diastereospecific manner. As opposed to the common 4-atom synthons in the previous literature reports, azoalkenes served as 3-atom synthons. Besides, the observed selectivity was supported by primary theoretical calculation. The unique chemistry of azoalkenes disclosed herein will empower asymmetric synthesis of nitrogen-containing ring structural motifs in a broader context.

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Chiral phosphoric acid catalyzed formal [3 + 2] cycloaddition reaction

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2,3-Dihydropyrroles were enantioselectively synthesized

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Azoalkenes served as 3-atom synthons

Metal and Oxidant-Free Brønsted Acid-Mediated Cascade Reaction to Substituted Benzofurans

Substituted hydroxy-benzofurans are easily accessible by treatment of resorcinols and 1,2-diaza-1,3-dienes (DDs) under acidic conditions. The reaction happens through an uncommon Michael reaction between aromatic derivatives as aromatic C(sp²)-H nucleophiles and DDs as acceptors. Also, the behavior of different phenols and 2-naphthol was investigated.

Recent Advances in the Chemistry of Conjugated Nitrosoalkenes and Azoalkenes

This review aims to present the most recent contributions in the chemistry of nitrosoalkenes and azoalkenes, highlighting the chemical behavior that makes them important and versatile building blocks in organic synthesis. These are heterodienes used in the assembly of a variety of heterocyclic systems, spanning from five- to seven-membered heterocycles, as well as for the functionalization of heterocycles.

Assembly of fully substituted 2,5-dihydrothiophenes via a novel sequential multicomponent reaction

A sequential multicomponent reaction between ketoesters, isothiocyanates and 1,2-diaza-1,3-dienes to create 2,5-dihydrothiophenes that can be converted into thiophenes.