Total Synthesis of (±)-20-epi-Kopsiyunnanine K: A Domino and Stereocontrolled Approach

A one-pot route to a novel azepane-fused tetrahydro-β-carboline framework from tryptyl-4-pentenamide derivatives has been developed, featuring the Rh-catalyzed hydroformylation double cyclization. Subsequent alkylation in the tetracyclic system proceeded stereoselectively to form a quaternary carbon. The synthesis of (±)-20-epi-kopsiyunnanine K was accomplished through the strategy.

Domino synthesis of 5-aminoimidazoles from Strecker multicomponent adducts via ytterbium-promoted isocyanide insertion/5-exo-dig cyclization

A new Lewis acid promoted domino isocyanide insertion/5-exo-dig cyclization of readily available Strecker 3-component adducts to 4-substituted 5-aminoimidazole derivatives is herein reported. Despite their potential as relevant heterocyclic scaffolds in medicinal chemistry programs, this class of compounds is still underrepresented, with current synthetic strategies poorly efficient in terms of timing and yields. To this end, we show how the exploitation of unconventional reactivities of isocyanides, promoted by ytterbium-triflate, could represent a key resource to enable a fast and easy access to such an unexplored area of the chemical space.

Selective Aerobic Oxidation of Alcohols in Low Melting Mixtures and Water and Use for Telescoped One-Pot Hybrid Reactions

An efficient, selective and sustainable protocol was developed for the CuCl₂/TEMPO/TMEDA‐catalyzed aerobic oxidation of activated alcohols to the corresponding carbonyl compounds using water or the environmentally friendly low melting mixture (LMM) d‐fructose‐urea as the reaction medium. Such oxidation reactions proceed under mild (room temperature or 40 °C) and aerobic conditions, with the carbonyl derivatives isolated in up to 98 % yield and within 4 h reaction time when using the above‐mentioned LMM. The potential application of this methodology is demonstrated by setting up useful telescoped, one‐pot two‐step hybrid transformations for the direct conversion of primary alcohols either into secondary alcohols or into valuable nitroalkenes, by combining oxidation processes with nucleophilic additions promoted by highly polarized organometallic compounds (Grignard and organolithium reagents) or with nitroaldol (Henry) reactions, respectively.

Synthesis of Saturated N-Heterocycles via a Catalytic Hydrogenation Cascade

Saturated N-heterocycles are prominent motifs found in various natural products and pharmaceuticals. Despite the increasing interest in this class of compounds, the synthesis of saturated bicyclic azacycles requires tedious multi-step syntheses. Herein, we present a one-pot protocol for the synthesis of octahydroindoles, decahydroquinolines, and octahydroindolizines through a cascade reaction.

Regioselective Synthesis of 4-Aryl-1,3-dihydroxy-2-naphthoates through 1,2-Aryl-Migrative Ring Rearrangement Reaction and their Photoluminescence Properties

4-Aryl-1,3-dihydroxy-2-naphthoates having the less accessible 1,2,3,4-tetrasubstituted naphthalene scaffold and that show photoluminescence emission from solid state as well as in solutions, were selectively synthesized from brominated lactol silyl ethers through the 1,2-aryl-migrative ring rearrangement reaction.

Synthesis of Terminally Fluorinated [7]Helicenes and Their Application to Photochemical Domino Reactions

The intramolecular Diels-Alder reactions of helicenes deform their π-conjugated screw-shaped skeletons. In particular, terminally tetrafluorinated [7]helicene (F₄ -[7]helicene) undergoes a photoinduced Diels-Alder reaction followed by a photoinduced double fluorine atom transfer. Herein, we thoroughly investigated this photochemical domino process by decreasing the level of fluorine substitution. F₃ -[7]Helicenes bearing two fluorine atoms at the dienophile terminal underwent photoinduced Diels-Alder reactions, but the whole domino process became slow. F₂ -[7]Helicene, which is difluorinated only at the dienophile terminal, was also photolabile. As a result, two fluorine atoms were sufficient for the photochemical domino reaction to occur. X-ray crystallographic analysis revealed that F₂ -[7]helicene was less compressed than F₄ -[7]helicene, indicating that terminal polyfluorination enhanced the intramolecular arene-fluoroarene stacking interactions and thus promoted the transformations.

Synthesis of β-Lactams and β-Homoprolines by Fragmentative Rearrangement of 5-Spirocyclopropaneisoxazolidines Mediated by Acids

Azetidinones and β-amino acids serve as useful building blocks in synthetic organic chemistry and their structural motifs are often found in biologically active compounds. Due to the importance of these compounds, several synthetic strategies have been developed and availability of new synthetic approaches is highly desirable. In this account, we describe the development of an original method that allows the preparation of β-lactam and β-homoproline derivatives not easily accessible through traditional processes. The serendipitous discovery made in our lab in 2000 involved the formation of a β-lactam by heating a mixture of an alkylidenecyclopropane tethered to a formyl group with N-methylhydroxylamine hydrochloride. Investigation of the process resulted in disclosing an alternative synthetic method of azetidinones based on an acid induced fragmentative rearrangement of cycloadducts of nitrones with suitable methylenecyclopropane derivatives. Herein, the scope of this process is reviewed. In addition, both experimental and computational studies of the mechanism for this peculiar fragmentative rearrangement are presented.

Thiophene Syntheses by Ring Forming Multicomponent Reactions

Thiophenes occur as important building blocks in natural products, pharmaceutical active compounds, and in materials for electronic and opto-electronic devices. Therefore, there is a considerable demand for efficient synthetic strategies for producing these compounds. This review focuses on ring-forming multicomponent reactions for synthesizing thiophenes and their derivatives.

Regio and stereoselective synthesis of anticancer spirooxindolopyrrolidine embedded piperidone heterocyclic hybrids derived from one-pot cascade protocol

Background

Spiropyrrolidine tethered piperidone heterocyclic hybrids were synthesized with complete regio- and stereoselectively in excellent yield via a tandem three-component 1,3-dipolar cycloaddition and subsequent enamine reaction in [bmim]Br. The synthesized compounds were evaluated for their anticancer activity against FaDu hypopharyngeal tumor cells.

Findings

Interestingly, most compounds displayed cytotoxicities similar to the standard anticancer agent bleomycin, with two of them (5a and 5g) being slightly more active than the reference drug.

Conclusion

Synthesized compounds have also been evaluated for their apoptosis-inducing properties in a cancer cell model, finding that treatment with compounds 5a–e led to apoptotic cell death.

Electronic supplementary material

The online version of this article (10.1186/s13065-018-0462-x) contains supplementary material, which is available to authorized users.

An unexpected Dimroth rearrangement leading to annelated thieno[3,2-d][1,2,3]triazolo[1,5-a]pyrimidines with potent antitumor activity

An unusual Dimroth rearrangement occurring in the reaction leading to annelated thieno[2,3-e][1,2,3]triazolo[1,5-a]pyrimidine core allowed the isolation of the linear isomer thieno[3,2-d][1,2,3]triazolo[1,5-a]pyrimidine. By decorating the linear isomer with the same chains that improved the biological activity of the angular isomers, new annelated thieno[3,2-d][1,2,3]triazolo[1,5-a]pyrimidines were designed and synthesized. They were selected by the Developmental Therapeutics Program (DTP) of the National Cancer Institute (NCI) for the anticancer screening against a panel of 60 human tumor cell lines. The biological results showed that the new derivatives exhibited strong antiproliferative activity up to nanomolar concentration. In vivo screenings of the most active compound, the N-[2-(1H-imidazol-4-yl)ethyl]-4-(3-phenyl-10-oxo-4,10-dihydrobenzothieno[3,2-d][1,2,3]triazolo[1,5-a]pyrimidin-4-yl)butanamide, showed its low toxicity and high potency.

Directed Metalation Linked to Transition Metal Catalyzed Cascade Reactions: Two Total Syntheses of Plicadin, the Alleged Coumestan from Psoralea plicata

The oxygen-rich heterocyclic compound 1-which was proposed to be the structure of plicadin, the alleged naturally occurring coumestan from the herb Psoralea plicata-was synthesized by the rational combinations of directed ortho and remote metalation reactions with cascades of Negishi, Sonogashira, Castro-Stephens, and carbamoyl Baker-Venkataraman reactions.

Radical Cyclization/β-Elimination Tandem Reactions: Enantiopure Sulfoxides as Temporary Chiral Auxiliaries

Alkylidene-substituted cyclopentane derivatives are formed in high enantiomeric purity by the reaction shown below. A highly diastereoselective radical cyclization is followed by elimination of a β-sulfinyl radical. Interestingly, the addition of the Lewis acid methylaluminum bis(2,6-di-tert-butyl-4-methylphenoxide) (MAD) totally reverses the stereochemical outcome of the reaction. E=CO₂ Me.

Modern Variants of the Mannich Reaction

Important building blocks for the synthesis of drugs or natural products are found in Mannich bases and their derivatives. Modern variants of the Mannich reaction that expand the potential of the classical intermolecular reaction significantly and enable efficient control of the regioselectivity and stereoselectivity are therefore the topic of intensive research. Intramolecular reactions, in particular as part of domino reaction sequences, often afford astoundingly simple and elegant approaches to complex target compounds.