1.Cycloaddition reactions
 

Solid State Melt Reaction (SSMR):

       Our research aims towards the development of new strategies that combine quantitative yields and high atom economy, while not requiring harsh reaction conditions such as toxic solvents, protecting groups, metal salts and oxidants / reductants. We approach this ultimate goal by using Solid State Melt Reaction (SSMR) where we melt the solid reactants for 1-2 hours which transforms the starting materials into the products. In recent years, we have demonstrated that this Solid State Melt Reaction (SSMR) methodology can be utilized for a large number of [4+2]-cycloaddition reactions to provide different kinds of complex polyheterocyclic architechtures via Domino Knoevenagel Hetero Diels-Alder Reaction (DKHDAR). In addition to [4+2] cycloaddition reaction, this novel methodology has been applied to Claisen Rearrangement for the construction of benzothiazole tethered chromanones and coumarins. Furthermore, this protocol has been applied for the synthesis of tetrasubstituted olefins via a rearrangement involving O-allyl to N-vinyl shift. Nevertheless, this methodology has found its use for synthesizing a wide variety of oxygen and nitrogen containing heterocycles and is a greener protocol in comparison to conventional methods.

[3+2]-Cycloaddition Reactions:

        We have been examining extensively the chemistry of substituted O-allylated salicylaldehyde derivatives in the last 17 years. We have developed a diverse array of major reactions associated with this starting material. Most significantly, we were able to develop highly regio- and stereoselective inter- and intramolecular [3 + 2] cycloadditions which provided a new class of heretocyclic scaffolds. 

     Types of cycloaddition reactions, which were used in our laboratory to design and synthesis the following complex poly heterocyclic frameworks are 

• Azomethine ylide cycloaddition

• Azomethine imine cycloaddition

• Carbonyl ylide cycloaddition

• Azide cycloaddition 

• Nitrone cycloaddition

• Nitrile oxide cycloaddition

2. Domino Reactions

Triple Domino Reactions (TDR):
 

      Using this methodology, we have synthesized diversified pyrazole/indoline linked chromenes in one pot synthesis fashion.
 

Multi-Component Quadruple & Double Quadrupole Domino Reactions (MCQDR & MCDQDR):

      A novel multicomponent quadruple domino reaction (MCQDR) for the assembly of structurally complex molecular architectures such as quinolinopyranpyrazole  & chromenopyranpyrazole derivatives via the formation of three rings and three contiguous stereogenic centers has been accomplished with high regio- and diastereoselectivity. Solvents, catalysts and work-up were not required to obtain the target molecules. In addition, this new protocol is also extended for the multicomponent double quadruple domino reaction (MCDQDR) to create novel polyheterocyclic architectures such as fused and bridged bicyclic chromenopyrnopyrazoles in an orthogonal manner.

3. Rearrangement Reactions

Claisen Rearrangement Reactions:

       A novel protocol has been successfully established for the efficient synthesis of benzothiazole-tethered chromanone/coumarin scaffolds via Claisen rearrangement using a solid state melt reaction (SSMR) in a one-pot manner. Benzothiazole formation and Claisen rearrangement involve the cleavage of S–S and C–O bonds and formation of C–S, C═N, and C–C bonds in a single operation without using a catalyst or solvent.
 

Discovery of New Rearrangement through 1,5-Vinyl Shift (Distal Vinyl Shift):

  A conceptually novel Distal Vinyl Shift (DVS) through quadruple domino reaction involving imine formation, oxazole/thiazole/oxazine formation, aza-Michael addition and selective retro oxa/aza-Michael addition leading towards N-vinyl benzoxazoles/benzothiazoles / N-vinyl 1, 3-benzoxazines has been developed for the first time. This reaction is highly stereoselective and was carried out efficiently without using any catalyst as well as column chromatography purification with wide substrate scope in very good to excellent yields.

4. C-H Activation

       C-H activation / functionalization is a more powerful emerging strategy and key step for directly generating the carbon–carbon or carbon-heteroatom bond formations from the inactivated desired C-H precursor. It is one of the simplest ways to reduce the number of steps of a given synthesis, which lessens the functional group manipulations typically required to obtain pre-oxidized substrates. It is the notion of step-economical and environmentally friendly synthesis emerged a domain of intense interest in current modern organic synthesis .

C-H activation/functionalization strategy 
       Among the various methods of C-H activation reactions, oxidative coupling and directing group assisted C-H activation reactions are more focused by many chemists. 
      Our research group mainly focused on directing group assisted ortho as well as meta C-H activation reactions using transition metal catalysts (Pd, Ru, Rh, Fe, Cu and Ag etc.,) to generate C-C bond / C-X bond formations and introducing new functional groups with high chemo, stereo and siteselectivity which is highly challenging and interesting task in organic synthesis. Using this strategy, we have constructed highly functionalized branched olefins as well as bioactive heterocyclic scaffolds under mild reaction conditions.

5. New Synthetic Methods and Reactions

     The ultimate goal of method development in organic synthesis is to provide useful and reliable tools for the synthesis of complex molecules such as natural products or biologically relevant compounds and to lead to a better understanding of the underlying principles. In our group, we are developing new methods which will provide access to useful building blocks that can be used to easily ensemble complex molecules. Therefore, the synthesis of new nitrogen and oxygen containing heterocycles is an important element of our research, not only to evaluate the potential of a new method, but also as a stimulus and source of inspiration towards new exciting discoveries.

6. Asymmetric synthesis
 

      The asymmetric research program in our laboratory is centred on the development of new synthetic methods for the preparation of enantiomerically pure compounds from simple and readily available starting materials by using efficient chiral catalysts that can deliver products in high enantiopurity, which is a prerequisite for present-day pharmaceutical applications. Our aim is not only to develop new methods but also application of our developed protocols for the preparation of biologically active substances.
 

Areas of our interest: 
1) Enantioselective synthesis of cyclic and heterocyclic compounds.
2) Organocatalytic formation of C-C bonds and study of tandem reactions leading to multiple C-C bond formation.
3) Development and synthesis of new bifunctional organic catalysts and their application.