Synthesis of Three‐Membered and Four‐Membered Heterocycles with the Assistance of Photochemical Reactions

Abstract

in Wiley Online Library (wileyonlinelibrary.com).Some transformations are not possible with ground-state reactions even in the presence of a catalyst; hence, they are performed under photochemical conditions. Electron transfer occurred even with the photochemical excitement of one molecule where redox reaction is not possible at the ground state. The side products were obtained from ground-state reactions. For C─C bond formation during photochemical reactions, there was no requirement of any chemical activation of the substrates. Therefore, these reactions are presented here for the synthesis of three-membered and four-membered heterocycles in the context of sustainable processes.

Impact of Excited-State Antiaromaticity Relief in a Fundamental Benzene Photoreaction Leading to Substituted Bicyclo[3.1.0]hexenes

“…Interestingly, it has been revealed that the activation barrier vanishes when going to the less symmetric pyrazine, and a lack of activation barrier has also been observed for silabenzene . We now confirm this feature for silabenzene at the CASPT2//CASSCF level (Figure ), and also for the pyridinium cation, which has a photochemistry which is of higher synthetic value than that of pyrazine. − Yet, at the lower CASSCF level, which contains only static electron correlation, there are still activation barriers, although they are smaller than for S 1 -state benzene. Thus, the activation barrier observed in the S 1 state of benzene is traceable to its high symmetry (for comparisons between the S 1 states of benzene, silabenzene, and pyridinium ion, see Table S19).…”

“…Clearly, ESAA alleviation seems to be a general process for 6π-electron cycles with S 1 states of ππ* character. The photochemistry of both silabenzene and pyridinium salts is established (for a summary, see Supporting Information, section 6), , and the mechanism and synthetic applications of pyridinium ion photochemistry (Scheme ) have been reviewed extensively. − Hence, the ESAA relief of 6π-electron cycles is a feature that triggers these molecules to undergo photo­rearrangements that can be of general synthetic utility. For example, 6-azabicyclo[3.1.0]­hexene, formed photochemically from pyridinium salts, can efficiently be transformed to polysubstituted cyclopentenes by acid-promoted ring opening (Scheme ).…”

Electrochemical Synthesis and Reactivity of Three‐Membered Strained Carbo‐ and Heterocycles

“…However, significant advances have been made toward the synthesis of three-membered carbocycles/heterocycles, and numerous methods are available in the literature for their synthesis. [3] At the same time, the high ring strain of these three-membered rings provides a considerable driving force for the ring opening functionalization products through CÀ C, CÀ N, and CÀ O bond cleavage. The traditional processes for the ring opening of these rings mostly depend upon the transition metal catalysis or usage of acids or thermolysis and proceed via ionic ring opening processes.…”

“…The synthesis of these highly strained ring systems was considered challenging because of their high reactivity. However, significant advances have been made toward the synthesis of three‐membered carbocycles/heterocycles, and numerous methods are available in the literature for their synthesis [3] . At the same time, the high ring strain of these three‐membered rings provides a considerable driving force for the ring opening functionalization products through C−C, C−N, and C−O bond cleavage.…”

Visible Light-Promoted Amide Bond Formation via One-Pot Nitrone in Situ Formation/Rearrangement Cascade

“…26 However, photopromoted rearrangement of nitrones into amides via a one-pot reaction has not been reported often. [27][28][29][30] In 2013, the Jamison group 31 demonstrated a photopromoted rearrangement of nitrones under continuous-flow conditions and provided a very general approach for amide bond formation. This reaction not only represented a novel and useful method for peptide fragment coupling but also expanded the scope of protein synthesis.…”