Exploring the reactivities of donor- acceptor cyclopropanes

Abstract

This thesis's main motive is to synthesized various functionalized heterocycles with the reactions of donor-acceptor cyclopropanes. Chapter-1: Introduction In modern synthetic chemistry, various small and strained molecules are harnessed as building blocks to synthesize complex compounds due to their high ring strain, easy accessibility, and diverse reactivity patterns. Cyclopropanes, the smallest three-membered carbocycles found in nature, are incredibly stable and have gained significant attention in organic chemistry, particularly as building blocks for the synthesis of cyclic and acyclic compounds. By adding donor and acceptor moieties at the vicinal position, cyclopropanes can be made reactive towards unsaturated compounds or polarophiles. The unique structural and electronic properties of cyclopropanes make them ideal and unique building blocks for a wide range of exciting transformations. Chapter-2A In the first part of chapter 2A I have developed Synthesis of Indole-Fused Dihydrothiopyrano Scaffolds via (3+3)-Annulations of Donor-Acceptor Cyclopropanes with Indoline-2-Thiones.The newly developed methodology provided access to a variety of indole-fused dihydrothiopyrano molecules in good to excellent yields. In addition, the we have described transformation of the furnished product into an N-fused thiazino indole molecule. Chapter-2B In the first part of chapter 2B I developed a straightforward and efficient LiAlH4-mediated protocol has been developed for the construction of thiazino indoles. This procedure provides efficient thiazino indoles derivatives in good to satisfactory yields. DFT calculation has been done to shed light into reaction mechanism. Chapter 3: In this study, I developed BF3·OEt2 Mediated (3+2) Cycloaddition Reactions of DACs with Cyanamides: Access to Cyclic Amidines. A BF3·OEt2 promoted facile synthesis of cyclic amidines has been developed via the (3+2)-cycloaddition of cyanamides with donoracceptor cyclopropanes (DACs). In addition to this, the protocol has been successfully extended to construct dimerized amidine derivative and gram-scale synthesis with great efficiency. Chapter 4: Nucleophilic Ring Opening of DACs through Umpolung Reactivity of Organochlorophosphines: Phosphine Oxide Functionalized Boron Pendanted Compounds. I present a BF3·OEt2 promoted protocol that offers umpolung reactivity of R1R2PCl/CN (R1, R2 = aryl, alkyl) towards donor-acceptor cyclopropanes (DACs) via nucleophilic ring-opening reactions to provide phosphinated O, O-chelated boron diester compounds. The newly established metaland additive-free one-pot multicomponent reaction protocol delivers the desired products in good to excellent yields under mild reaction conditions. The compounds exist in both the forms- keto and enol, with the majority being in the keto form, according to NMR analysis. The enolic form is identified by single crystal XRD analysis and DFT calculations indicate that the keto form is more stable than the corresponding enolic form. Chapter 5. In this chapter, I present a comprehensive summary of the work accomplishments in the thesis entitled as “Exploring the Reactivities of Donor-Acceptor Cyclopropanes”.