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.

The Castagnoli–Cushman Reaction

Since the first reports of the reaction of imines and cyclic anhydrides by Castagnoli and Cushman, this procedure has been applied to the synthesis of a variety of lactams, some of them with important synthetic or biological interest. The scope of the reaction has been extended to the use of various Schiff bases and anhydrides as well as to different types of precursors for these reagents. In recent years, important advances have been made in understanding the mechanism of the reaction, which has historically been quite controversial. This has helped to develop reaction conditions that lead to pure diastereomers and even homochiral products. In addition, these mechanistic studies have also led to the development of new multicomponent versions of the Castagnoli–Cushman reaction that allow products with more diverse and complex molecular structures to be easily obtained.

Synthesis of imidazolocoumarins by the amide-directed oxidative cyclisation of enol-Ugi derivatives

The oxidative C(sp³)-H intramolecular imination of hydroxycoumarin enol-Ugi adduct derivatives affords selectively diversely substituted imidazolocoumarins in one pot. The amide group derived from the enol-Ugi isocyanide component directs the functionalisation of the adjacent C(sp³)-H and then is lost as an isocyanate molecule in an unprecedented transformation. This strategy was applied for the synthesis of potential modulators of innate immune system receptor TLR7, which showed high binding affinities in the molecular docking studies.

Selective Synthesis of 3-Substituted Pyrrolidinones by Enol-Passerini and Anomalous Enol-Passerini Condensations

Enols are used for the first time in a condensation with aldehydes and isocyanides to selectively give three- or pseudo-four-component adducts, depending on the reaction conditions. These new transformations have proven to be a convenient alternative for the synthesis of biologically relevant pyrrolidinones containing peptidic or pseudo-peptidic groups on carbon 3. More importantly, this work attests to the utility of heterocyclic enols containing conjugated electron-withdrawing groups as useful reagents in isocyanide-based multicomponent reactions.

Enols as feasible acid components in the Ugi condensation

Heterocyclic enols are used for the first time as acid components in an Ugi-type multicomponent condensation. For that purpose, we have chosen enols containing a Michael acceptor, in order to facilitate an irreversible rearrangement of the primary Ugi adduct. The new four-component process leads readily and efficiently to heterocyclic enamines containing at least six elements of diversity.

Conjugate addition of isocyanides to chromone 3-carboxylic acid: an efficient one-pot synthesis of chroman-4-one 2-carboxamides

We report a novel Lewis acid catalysed tandem reaction of isocyanides, chromone 3-carboxylic acid and nucleophiles. An experimentally very simple procedure, involving the use of microwave irradiation in the presence of a Lewis acid catalyst, affords a representative collection of chromone-2-carboxamides and chromone-2-carboxamido-3-esters in high yields, in just a few minutes. Such an unprecedented strategy is formally equivalent to a conjugate addition of isocyanides to Michael acceptors.

Sequential five-component synthesis of spiropyrrolidinochromanones

Herein we report a novel, diastereoselective, one-pot, two-step, sequential synthesis of highly functionalized natural product-like spiropyrrolidinochromanones. The process consists of an Ugi four-component condensation of 3-formylchromones with amines, isocyanides, and glyoxylic acids followed by a nucleophilic conjugate addition and intramolecular cyclization. The experimental simplicity and tolerance to a wide variety of substituents makes this method suitable for combinatorial synthesis.

Indene and Pseudoazulene Discotic Liquid Crystals: A Synthetic and Structural Study

Several new liquid-crystalline indene and pseudoazulene systems are reported. These molecules give rise to either columnar hexagonal mesophases and/or columnar plastic phases. The unique nature of these compounds stems from their non-classical discotic structure. Although the molecules have rigid aromatic cores, they lack terminal tails and instead the polarizable atoms (S, halogens) or polar groups (CN, CO) act as unusual soft parts. On the basis of many structurally related materials, we conclude that for this type of compound molecular stacking in the solid state is a prerequisite for the appearance of a columnar mesophase, although other intermolecular interactions within the layers are also important in establishing liquid-crystalline order. The behavior reported for these mesomorphic molecules opens up new possibilities in the search for related molecular interactions that might be useful for the construction of supramolecular architectures with particular properties.

Cyclopentathiadiazines, new heterocyclic materials from cyclic enaminonitriles

Indene and cyclopentene enaminonitriles were reacted with SCl2, iBu3N and NCS to give the first cyclopenta[1,2,6]thiadiazines that showed unusual characteristics, one as a NIR dye and another as a liquid crystal.

Base-Induced Photocyclization of 1,2-Diaryl-1-tosylethenes. A Mechanistically Novel Approach to Phenanthrenes and Phenanthrenoids

The irradiation with UV light of a number of 1,2-diaryl-1-tosylstilbenes, in the presence of base, leads to the corresponding phenanthrenes and heterocyclic analogues. These results are consistent with a mechanism involving the base-induced elimination of p-toluenesulfinic acid from an intermediate 9-tosyl-4a,4b-dihydrophenanthrene, formed by photochemical cyclization of the starting 1,2-diaryl-1-tosylstilbenes. [reaction: see text]