Stefano Marcaccini: a pioneer in isocyanide chemistry

Stefano Marcaccini was one of the pioneers in the use of isocyanide-based multicomponent reactions in organic synthesis. Throughout his career at the University of Florence he explored many different faces of isocyanide chemistry, especially those geared towards the synthesis of biologically relevant heterocycles. His work inspired many researchers who contributed to other important developments in the field of multicomponent reactions and created a school of synthetic chemists that continues today. In this manuscript we intend to review the articles on isocyanide multicomponent reactions published by Dr. Marcaccini and analyse their influence on the following works by other researchers. With this, we hope to highlight the immense contribution of Stefano Marcaccini to the development of isocyanide chemistry and modern organic synthesis as well as the influence of his research on future generations. We believe that this review will not only be a well-deserved tribute to the figure of Stefano Marcaccini, but will also serve as a useful inspiration for chemists working in this field.

Uncatalyzed diastereoselective synthesis of alkyliminofurochromone-derived benzylmalononitriles via a three-component cascade reaction: competition between Diels-Alder cycloaddition and Michael addition

Diastereoselective Michael addition reactions of 3-(alkylamino)-9H-furo[3,4-b]chromen-9-one intermediate, produced from the [1 + 4] cycloaddition/tautomerization reaction between 3-formylchromones and alkyl isocyanide in dry CH₂Cl₂, with arylidene malononitrile were developed to afford a wide range of functionalized 2-((S)-((R,Z)-3-(alkylimino)-9-oxo-3,9-dihydro-1H-furo[3,4-b]chromen-1-yl)(aryl)methyl)malononitrile derivatives in good yields and excellent diastereoselectivities under mild conditions. Excellent diastereoselectivity has been achieved to yield products containing two stereogenic carbons and one stereogenic imine group. Two C-C and one C-O bonds were selectively formed to provide new alkylated iminofurochromones in good yields.

Catalyst-free and additive-free reactions enabling C-C bond formation: a journey towards a sustainable future

This review focuses on the catalyst- and additive-free C-C bond forming reactions reported mostly from the year 2005 to date. C-C bond forming reactions are highly important as large and complex organic molecules can be derived from simpler ones via these reactions. On the other hand, catalyst- and additive-free reactions are economical, environmentally friendly and less sensitive to air/moisture, allow easy separation of products and are operationally simple. Hence, a large number of research articles have been published in this area. Though a few reviews are available on the catalyst-free organic reactions, most of them were published a few years ago. The current review excludes catalysts as well as additives and is specific to only C-C bond formation. Besides many organic name reactions, catalyst/additive-free C-H functionalizations, coupling reactions and UV-visible-light-promoted reactions are also discussed. Undoubtedly, the contents of this review will motivate readers to do more novel work in this area which will accelerate the journey towards a sustainable future.

Xanthones and Cancer: from Natural Sources to Mechanisms of Action

Xanthones are a class of heterocyclic natural products that have been widely studied for their pharmacological potential. In fact, they have been serving as scaffolds for the design of derivatives focusing on drug development. One of the main study targets of xanthones is their anticancer activity. Several compounds belonging to this class have already demonstrated cytotoxic and antitumor effects, making it a promising group for further exploration. This review therefore focuses on recently published studies, emphasizing their natural and synthetic sources and describing the main mechanisms of action responsible for the anticancer effect of promising xanthones.

A catalyst-free aqueous mediated multicomponent reaction of isocyanide: expeditious synthesis of polyfunctionalized cyclo[b]fused mono-, di- and tricarbazoles

A new multi-component reaction is developed for the synthesis of cyclo[b]fused mono-, di- and tricarbazoles from o-alkenyl arylisocyanides, aldehydes, and cyclic diketones in ethanol/water (1 : 1) as the solvent system.

Recent advances in the synthesis of xanthones and azaxanthones

A useful chemical toolbox for (aza)xanthones from 2012 to 2020 that covers the optimization of known procedures and novel methodologies.

Application of E1cB Elimination in Asymmetric Organocatalytic Cascade Reactions To Construct Polyheterocyclic Compounds

By introducing a carbon functionality at 2-position of chromane, the formal asymmetric functionalization of the 3-position of 2-substituted chromane has been realized via a highly chemo-, regio-, and stereoselective organocatalytic cascade reaction in a sequential one-pot manner involving an E1cB mechanism governed ring-opening process. Critical to our success was the design of a chiral dipeptide-based bifunctional acid-base organocatalyst, which exhibited high catalytic activity at low catalyst loading (1-0.1 mol %), leading to biologically interesting polyheterocyclic compounds.

Pd-Catalyzed sequential hydroarylation and olefination reactions of 3-allylchromones

In this paper, a novel approach to regioselective α- or γ-hydroarylation of 3-allylchromones with electron-rich arenes has been presented. Results of this study indicated that the regioselectivity was dependent on the substituent at the γ-position of the allyl group. Hydrogen or alkyl substitution favored α-hydroarylation, whereas aryl substitution favored γ-hydroarylation. This methodology provides an efficient means to achieve the α- or γ-selective hydroarylation of 3-allylchromones. Application of α-hydroarylation to perform Pd-catalyzed one-pot sequential α-hydroarylation and π-chelation-assisted olefination has also been reported.

Cesium-Carbonate-Mediated Benzalation of Substituted 2-Aryl-3-nitro-2 H-chromenes with Substituted 4-Benzylidene-2-phenyloxazol-5(4 H)-ones

Cs₂CO₃-mediated domino benzalation reaction with a variety of 2-aryl-3-nitro-2 H-chromenes and 4-benzylidene-2-phenyloxazol-5(4 H)-ones has been realized. The reaction proceeds smoothly with a broad substrate scope, thus providing a variety of substituted ( Z)-4-(( Z)-benzylidene)chroman-3-one oximes in moderate to high yields, which were easily transformed into biologically important 4 H-chromeno[3,4- c]isoxazoles.

[1 + 2 + 3] Annulation as a General Access to Indolo[3,2- b]carbazoles: Synthesis of Malasseziazole C

A formal [1 + 2 + 3] annulation of methyleneindolinones with o-alkenyl arylisocyanides has been developed for the general and efficient synthesis of both symmetrical and unsymmetrical indolo[3,2- b]carbazoles. The chemoselectivity of this domino reaction was tuned by a tethered alkenyl group, which enables successive formation of three new bonds and two rings from readily accessible starting materials in a single operation. Furthermore, this methodology was used as a key step in the synthesis of the alkaloid malasseziazole C.

Tandem synthesis of 4-aminoxanthones is controlled by a water-assisted tautomerization: a general straightforward reaction

Iminolactone-aminofuran tautomerization is the rate-determining step in the multicomponent synthesis of xanthones from 3-carbonylchromones, isocyanides and dienophiles.

Formal [1 + 2 + 3] Annulation: Domino Access to Carbazoles and Indolocarbazole Alkaloids

A new formal [1 + 2 + 3] annulation of o-alkenyl arylisocyanides with α, β-unsaturated ketones under metal-, base-, and acid-free conditions is disclosed. This domino reaction provides a general protocol for the efficient and practical synthesis of a wide range of carbazole derivatives from readily available starting materials in a single operation. Furthermore, this methodology was used as the key step in a protecting-group-free synthesis of indolocarbazole alkaloids arcyriaflavin A and racemosin B.

Synthesis of 3-(2-Olefinbenzyl)-4H-chromen-4-one through Cyclobenzylation and Catalytic C-H Bond Functionalization Using Palladium(II)

An efficient strategy for synthesizing 3-(2-olefinbenzyl)-4H-chromen-4-one in two steps was developed. The first step is a cyclobenzylation reaction between (E)-3-(dimethylamino)-1-(2-hydroxyphenyl)prop-2-en-1-one and benzyl bromide to produce homoisoflavonoid. The second step involves intermolecular Pd-catalyzed π-chelating-assisted C-H bond olefination. Using the C-2/C-3 double bond of chromone, palladium-catalyzed aryl C-H bond activation can be functionalized to generate ortho-olefination derivatives in moderate to high yields.

Isocyanide-based multicomponent reactions in the synthesis of heterocycles

In this review, we update our previous presentation, underscoring the recent applications of isocyanides as privileged synthons in the synthesis of various heterocyclic compounds, especially focused on those synthesizedviamulticomponent reactions.

A facile strategy for accessing 3-alkynylchromones through gold-catalyzed alkynylation/cyclization of o-hydroxyarylenaminones

A strategy based on tandem alkynylation ofo-hydroxyarylenaminones followed by intramolecular cyclization has been developed to generate a diverse array of 3-alkynyl chromones.

Synthesis of 4-quinolones, benzopyran derivatives and other fused systems based on the domino ANRORC reactions of (ortho-fluoro)-3-benzoylchromones

This method provides a valuable one-pot shortcut for the synthesis of 4-quinolones, benzopyran derivatives and other fused systems from (ortho-fluoro)-3-benzoylchromones.