Development of New Synthetic Strategies, Tactics and their Applications.

This account covers our work related to the development of various synthetic methodologies since 1994. We summarized our strategies and their application to design various functional molecules. In this regard, we also report the utility of our methodologies in others research work. These methods we report here are simple and efficient for the synthesis of a wide variety of intricate molecules such as heterocycles, polycycles, unusual α-amino acids, star-shaped molecules, and modified peptides. For this purpose, we used various transition metal-based reagents and catalysts. Various popular reactions such as metathesis, Suzuki coupling, [2+2+2] cyclotrimerization were used to assemble these targets. Moreover, rongalite has been used to expand the Diels-Alder chemistry.

Design and Synthesis of Polycycles, Heterocycles, and Macrocycles via Strategic Utilization of Ring-Closing Metathesis.

In this perspective, we summarize new synthetic approaches for the construction of various polycyclic compounds involving ring-closing metathesis as a key step. In this regard, we used ring-closing metathesis in combination with other popular reactions like Suzuki-Miyaura coupling, Claisen rearrangement, Fischer indolization, Grignard addition, Diels-Alder reaction, and [2+2] cycloaddition reaction etc. To this end, a variety of functional molecules such as α-amino acids, cyclophanes, heterocycles, propellanes, spirocycles, and macrocycles have been prepared. The strategies developed and the molecules prepared here play a key role in designing new materials and also act as lead compounds in drug design. The strategies and tactics developed here are useful to design polycycles, macrocycles, and heterocycles of diverse ring systems.

Synergistic approach to polycycles through Suzuki-Miyaura cross coupling and metathesis as key steps.

This account provides an overview of recent work, including our own contribution dealing with Suzuki-Miyaura cross coupling in combination with metathesis (or vice-versa). Several cyclophanes, polycycles, macrocycles, spirocycles, stilbenes, biaryls, and heterocycles have been synthesized by employing a combination of Suzuki cross-coupling and metathesis. Various popular reactions such as Diels-Alder reaction, Claisen rearrangement, cross-metathesis, and cross-enyne metathesis are used. The synergistic combination of these powerful reactions is found to be useful for the construction of complex targets and fulfill synthetic brevity.

Recent applications of ring-rearrangement metathesis in organic synthesis.

Ring-rearrangement metathesis (RRM) involves multiple metathesis processes such as ring-opening metathesis (ROM)/ring-closing metathesis (RCM) in a one-pot operation to generate complex targets. RRM delivers complex frameworks that are difficult to assemble by conventional methods. The noteworthy point about this type of protocol is multi-bond formation and it is an atom economic process. In this review, we have covered literature that appeared during the last seven years (2008-2014).

Synthetic Approaches to Star-Shaped Molecules with 1,3,5-Trisubstituted Aromatic Cores.

Herein, we summarize the synthetic approaches that have been developed for the synthesis of star-shaped molecules. Typically, to design such highly functionalized molecules, simple building blocks are first assembled through trimerization reactions, starting from commercially available starting materials. Then, these building blocks are synthetically manipulated to generate extended star-shaped molecules. We also discuss the syntheses of star-shaped molecules that contain 2,4,6-trisubstituted 1,3,5-triazine or 1,3,5-trisubstituted benzene rings as a central core and diverse substituted styrene, phenyl, and fluorene derivatives at their periphery, which endows these molecules with extended conjugation. A variety of metal-catalyzed reactions, such as Suzuki, Buchwald-Hartwig, Sonogashira, Heck, and Negishi cross-coupling reactions, as well as metathesis, have been employed to functionalize a range of star-shaped molecules. The methods described herein will be helpful for designing a wide range of intricate compounds that are highly valuable in the fields of supramolecular chemistry and materials science. Owing to space limitations, we will not cover all of the publications on this topic. Instead, we will focus on examples that were reported by our research group and other relevant recent literature. Apart from the trimerization sequence, this Minireview has been structured based on the key reactions that were used to prepare the star-shaped molecules and other higher analogues. Finally, some examples that do not fit into this classification are discussed.

Application of Claisen Rearrangement and Olefin Metathesis in Organic Synthesis.

Several new synthetic methods to diverse polycycles and heterocycles on the basis of [3,3]-sigmatropic rearrangement and ring-closing metathesis as key steps are summarized. In this regard, Claisen, aza-Claisen, and Overman rearrangements are used in combination with other popular reactions such as ring-closing metathesis, Suzuki coupling, Diels-Alder reaction, and retro-Diels-Alder reaction. To this end, we prepared polycycles (e.g., cyclophanes, cage molecules), heterocycles (e.g., oxepins, azapins), carbocycles, and spirocycles with the use of the above protocol.

Advanced approach to polycyclics by a synergistic combination of enyne metathesis and Diels-Alder reaction.

Enyne metathesis (EM) has widely been used to prepare various synthetic and natural products. Further, a sequential use of EM and Diels-Alder (DA) reactions generates highly functionalized and intricate polycarbocycles and heterocyclic frameworks. In this critical review we describe the application of a unique combination of EM and DA reactions to prepare various amino acid derivatives, natural products and heterocycles. Some of the heterocyclic targets include cyclic peroxides, siloxanes and various nitrogen (or oxygen) containing compounds. Use of ethylene and cyclooctadiene (COD) for improving the yield of EM products are also discussed (69 references).