PHOTOINDUCED ORGANIC TRANSFORMATIONS OF OLEFINS AND CARBONYL COMPOUNDS

Abstract

There are seven chapters in the thesis. The purpose and scope of the effort are introduced in the first chapter. Unsaturated hydrocarbons containing at least one double bond between carbon atoms are known as alkenes. They are adaptable building blocks in the synthesis of organic compounds because of their reactivity, which enables them to take part in a variety of reactions. Carbene and carbenoid reactions, radical reactions, olefin metathesis, addition reactions, and olefin metathesis are a few important reactions involving alkenes. Similar to this, the reactivity of the carbonyl group makes carbonyl compounds very helpful in the synthesis of organic molecules. Nucleophilic addition processes, redox reactions, aldol reactions, acylation reactions, alkene production reactions, etc. are a few important reactions involving ketones. Under photoinduced circumstances, these two synthons have a great deal of potential to produce significant organic derivatives. Alkenes and carbonyls are discussed briefly in Chapter 2 as the most fundamental and practical synthons used to produce atom- and step-efficient heterocyclic compounds, which are essential ingredients in many pharmaceuticals, natural products, and significant intermediates in modern synthetic chemistry. Furthermore, because of their many physical, chemical, and biological characteristics, nitrogen-based motifs have grown to be crucial to material and pharmaceutical chemistry. The nitrogen scaffold has been decorated with numerous functional groups using novel synthetic techniques and procedures. It is highly intriguing to create a novel photo-induced catalysis approach that can be applied to chemical synthesis in a variety of ways. It is feasible to convert light into chemical energy using this state-of-the-art technology. Due to its low price and environmental friendliness, it is a good and sustainable substitute for traditional catalysis. Since nitrogen scaffolds are present in > 50% of all medicinal and functional materials, creating an effective synthetic process employing a photo-induced approach has become a valuable tool in recent years. This study focuses on some of the most significant recent advances in the subject, including the clarification of light's effects, the encouragement of fundamental-coupling stages, the selective functionalization of amines, the employment of complementary mechanistic concepts, and synthetic applications. In Chapter 3, two-step, one-pot, light-promoted syntheses of imidazo[1,2-a]pyridines and quinoxalines from alkynes and alkenes, respectively, are discussed. The transformations take place when acetonitrile and water are exposed to UV LED fluorescent black light (380–390 nm), which causes the synthesis of α,α′-dibromo ketones or α-bromo ketones. There is no need for a sensitizer, catalyst, or additives with this approach. This one-pot two-step procedure, which offers broad functional group tolerance, is a new addition to the synthetic methods available for quinoxaline and imidazopyridine derivatives via light-promoted intramolecular through-space charge transfer from amine center to a carbonyl group. Knoevenagel condensation is widely used in organic synthetic chemistry and several reaction conditions have been demonstrated. These reactions in a neutral medium are challenging. In chapter 4, we present a sustainable and greener method for Knoevenagel condensation reaction between carbonyl compounds (both aldehydes and ketones) and active methylene compounds using Rose Bengal as a photosensitizer in an aqueous medium. This protocol works smoothly for aromatic aldehydes and ketones containing both electron-donating and electron-withdrawing substituents. It is a common procedure in synthetic organic chemistry to deconstruct alkenes into their carbonyl derivatives, and numerous reaction conditions for electron-rich and unconjugated alkenes have been established. However, such conjugated and electron-deficient alkene reactions are quite difficult. In chapter 5, we showed that under milder and more environmentally friendly circumstances, light-promoted water-mediated NBS photoinitiated cleavage of electron-deficient conjugated alkenes may occur. This approach is also shown to include a deprotection phase for carbonyl groups. This method operates in an aqueous medium with a broad functional group tolerance and good regioselectivity at room temperature. The visible-light-induced catalyst-free condition for thiol self- and cross-coupling reactions in an ambient environment has been established in chapter 6. Further, the synthesis of β-hydroxysulfides is accomplished under very mild conditions involving the formation of an electron donor-acceptor (EDA) complex between a disulfide and an alkene. However, the direct reaction of thiol with alkene via the formation of a thiol-oxygen co-oxidation (TOCO) complex failed to produce the desired compounds in high yields. The protocol was successful with several aryl and alkyl thiols for the formation of disulfides. However, the formation of β-hydroxysulfides required an aromatic unit on the disulfide fragment, which supports the formation of the EDA complex during the course of the reaction. The approaches presented in this paper for the coupling reaction of thiols and the synthesis of β-hydroxysulfides are unique and do not require toxic organic or metal catalysts. An overview of the research on treating alkenes with hydroxyl radical species when other electron-deficient radical species, such as bromines and thiols, are present is given in chapter 7. This chapter compares the reactivity of different alkene species in the presence of similar radical initiators. For example, alkenes with electron-donating and neutral functional groups in the terminal position or alkenes with electron-withdrawing groups in the terminal position exhibit different reactivity.