Sushobhan Chowdhury

Recent developments in solvent-free multicomponent reactions: a perfect synergy for eco-compatible organic synthesis

Multicomponent reactions have gained significant importance as a tool for the synthesis of a wide variety of useful compounds, including pharmaceuticals. In this context, the multiple component approach is especially appealing in view of the fact that products are formed in a single step, and the diversity can be readily achieved simply by varying the reacting components. The eco-friendly, solvent-free multicomponent approach opens up numerous possibilities for conducting rapid organic synthesis and functional group transformations more efficiently. Additionally, there are distinct advantages of these solvent-free protocols since they provide reduction or elimination of solvents thereby preventing pollution in organic synthesis “at source”. The chemo-, regio- or stereoselective synthesis of high-value chemical entities and parallel synthesis to generate a library of small molecules will add to the growth of multicomponent solvent-free reactions in the near future. In this review we summarized the results reported mainly within the last 10 years. It is quite clear from the growing number of emerging publications in this field that the possibility to utilize multicomponent technology allows reaction conditions to be accessed that are very valuable for organic synthesis. Therefore, diversity oriented synthesis (DOS) is rapidly becoming one of the paradigms in the process of modern drug discovery. This has spurred research in those fields of chemical investigation that lead to the rapid assembly of not only molecular diversity, but also molecular complexity. As a consequence multi-component as well as domino or related reactions are witnessing a new spring.

ortho-Quinone methide (o-QM): a highly reactive, ephemeral and versatile intermediate in organic synthesis

Since its first observation in 1907, ortho-quinone methide (o-QM) has occupied a strategic place within the framework of reactive intermediates in organic synthesis. In recent years, o-QM has enhanced its importance as a versatile reactive intermediate, and its applications in organic synthesis, material chemistry, fine chemicals, and pharmaceuticals are increasing rapidly. This critical review summarizes the key concepts behind o-QMs and provides an overview of current applications in organic synthesis to provide an appropriate background for synthetic, medicinal and combinatorial developments. This review covers the literature from its origin to the mid of 2014 (112 references).

Regioselective synthesis of tetrahydrothiochromen-5-ones via a one-pot three-component solvent-free domino protocol.

A highly efficient one-pot three-component regioselective synthesis of 4-aryl-3-aroyl-2-methylsulfanyl-4,6,7,8-tetrahydrothiochromen-5-ones has been developed by annulation of β-oxodithioesters with aldehydes and cyclic 1,3-diketones under solvent-free conditions promoted by P(2)O(5). No cocatalyst or activator is needed in this protocol. The merit of this process is highlighted by its high efficiency of producing three new bonds and a stereocenter in one operation.

Palladium catalyzed oxidative coupling of α-enolic dithioesters: a new entry to 3,4,5-trisubstituted 1,2-dithioles via a double activation strategy.

An operationally simple, facile, and convenient one-pot straightforward method for the construction of 3,4,5-trisubstituted 1,2-dithioles has been explored and developed via palladium catalyzed self-coupling of α-enolic dithioesters for the first time. Pd(0) efficiently catalyzes the activation and cleavage of S-H and C-S bonds to achieve cascade coupling, which results in the concomitant formation of new S-S and C-C bonds. Optimization data, substrate scope, and mechanistic insights are discussed.

CuSO4–D-glucose, an inexpensive and eco-efficient catalytic system: direct access to diverse quinolines through modified Friedländer approach involving SNAr/reduction/annulation cascade in one pot

A highly efficient and scalable multicomponent domino reaction for the synthesis of functionalized/annulated quinolines is devised directly from 2-bromoaromatic aldehydes/ketones in H2O–EtOH mixture for the first time. The key to this reaction is the use of an air-stable, eco-efficient and inexpensive CuSO4–D-glucose catalyst system, which is able to catalyze multiple transformations in one pot. The approach is carbon-economic and relies on sequential SNAr/reduction/Friedlander annulation steps, forming C–C and C–N bonds by cleavage of the Csp2–Br bond in a single synthetic operation. The reaction has a broad substrate scope and affords products in good to excellent yields.

Organocatalyzed straightforward synthesis of highly fluorescent 3,5-disubstituted 2,6-dicyanoanilines via domino annulation of α-enolicdithioesters with malononitrile

Piperidine mediated a robust, efficient, and selective one-pot synthesis of previously inaccessible and highly fluorescent 3,5-disubstituted 2,6-dicyanoanilines. This was achieved via the domino carboannulation of α-enolicdithioesters with malononitrile by dehydrative CO/CS bond functionalization. It is presumed that the domino sequence includes base promoted nucleophilic addition, Knoevenagel condensation and ANRORC (addition of nucleophile/ring opening/ring closure) steps. The screening for optical properties identified a strong blue emission with high fluorescence quantum yields.