Organocatalyzed and photoinduced synthetic strategies for the formation of diverse C–C and C heteroatom bonds

Abstract

Chapter 1: Introduction To pursue the above thought process, a detailed literature studies on organocatalysis and photocatalysis was carried out in chapter 1, introduction part. Over the years, organocatalysis remained a main pillar in organic synthesis to achieve various enantioenriched products promptly and efficiently. Various organocatalysts have been developed over the year, amidst chiral secondary amine-based Hayashi-Jørgensen catalyst is a prime member. They can integrate orthogonal activation of carbonyls via HOMO-raising and the LUMO-lowering technique to access valuable building blocks and new scaffolds. In recent times, visible light has gained tremendous attention from the synthetic community as a renewable source, and its robustness promotes versatile synthetic strategies. Photoexcitation of organic molecules can drive noteworthy transformation, usually inaccessible via traditional thermal routes, leading to the construction of several important cyclic and acyclic structural motifs. Chapter 2: Asymmetric Organocatalytic Double 1,6-Addition: Rapid Access to Chiral Chromans with Molecular Complexity In this chapter, we have disclosed an organocatalytic asymmetric route for the synthesis of chroman derivatives with remarkable selectivity (up to >20:1 d.r., >99% ee) and moderate to good yield (up to 96%). The reaction starts with an oxa-Michael (1,6-addition) with exclusive δ-site selectivity took place to a vinylogous unbiased iminium-ion, followed by a vinylogous dienamine based another 1,6-addition to the p-QMs. This work illustrates a rare example of double 1,6-addition under Jørgensen–Hayashi catalysts. The sluggish reactivity of δ-aryl substituted unbiased 2,4-dienals was dramatically influenced by using β, δ- aryl-substituted 2,4-dienals. The α, β-unsaturated enal functionality present in the chiral chroman moiety gave an opportunity to introduce molecular complexity with high reactivity and stereoselectivity. Chapter 3: Photoinduced Diverse Reactivity of Diazo Compounds with Nitrosoarenes This chapter showcases the divergent role of a different class of photoexcited diazo compounds towards nitrosoarenes to deliver a wide range of α-ketoester and 1,2-oxazetidin-3-one derivatives in the absence of transition metal, catalyst using milder reaction conditions. The reaction was facilitated by the generation of carbene intermediate and in situ formation of ketene intermediate under light harvesting conditions. A versatile substrate scope was tolerated under the developed reaction conditions to deliver the desired product in moderate to good yield (up to 83%). Finally, the synthetic applicability of the developed protocol illustrates a one-pot synthesis of α-ketoester and transformation of cycloadduct to deliver synthetically beneficial compounds. Chapter 4: Introducing N-Sulfinylamines into Visible-Light-Induced Carbene Chemistry for the Synthesis of Diverse Amides and α-Iminoesters Alike previous chapter, this chapter demonstrates another exciting result on carbene chemistry, where different kinds of carbene precursors are brought into play with rarely explored reactivities of N-sulfinylamine chemistry, through a visible-light-induced manifold to render versatile amide and α iminoester derivatives The reaction conditions are mild, benign, easy to set up and scalable. The collective data, including UV-visible spectra, light on/off experiments, and other mechanistic studies, support the proposed mechanism. Further efforts for portraying the synthetic applicability of the developed protocol were carried out by late-stage functionalization of diazo esters derived from naturally occurring secondary alcohols and direct installation of unprotected amines and imines over diazo compounds by utilizing the sporadically explored reactivity of N-silylsulfinylamine. Chapter 5: Visible-Light-Mediated (sp3)Cα–H Functionalization of Ethers Enabled by Electron Donor-Acceptor Complex In order to explore more reactivities of diazo compounds in this last chapter, we have developed a modular method for C(sp2)–H and C(sp3)–H functionalization to render a series of amines with various ethers. Visible lights were vital for this metal-free, oxidant-free C–N and C–C bond construction. The formation and characterization of catalytic NBS-THF electron donor-acceptor (EDA) complex were crucial, permitting direct and selective (sp3)Cα–H amination event. Based on the literature and our experimental evidence a radical chain mechanism was proposed. The developed methodology overcomes the major disadvantages like long reaction time and harsh reaction conditions connected with previously reported (sp3)Cα–H bond functionalization methods.