Elemental sulfur as the “S” source: visible-light-mediated four-component reactions leading to thiocyanates

Abstract

An eco-friendly and photocatalyst-free visible-light-promoted four-component reaction of α-diazoesters, elemental sulfur, cyclic ethers and TMSCN leading to thiocyanates is described.

Visible photons as ideal reagents for the activation of coloured organic compounds

“…The capability of carbenes to activate cyclic ethers was thoroughly investigated through a dual experimental and computational approach, which confirmed the formation of the oxonium ylide 86.5 as the key step. 293,294 In this context, THF was intensively exploited for the development of a wide range of multicomponent processes, for the synthesis, among the others, of thiocyanates 87.2a-c (in the presence of elemental sulfur and trimethylsilyl cyanide, Scheme 87a), 295 S-alkyl dithiocarbamates, 296 organophosphorus derivatives 87.4a-c (under aerated conditions in the presence of phosphine oxides as the coupling partner, Scheme 87b), 297 polysubstituted nitrogen-based heterocycles 298,299 and 1,3-diketones. 298 The formation of an ylide intermediate between a cyclic ether and a carbene was the key step of a ring expansion/ contraction process.…”

“…In this context, THF was intensively exploited for the development of a wide range of multicomponent processes, for the synthesis, among the others, of thiocyanates 87.2a–c (in the presence of elemental sulfur and trimethylsilyl cyanide, Scheme 87a), 295 S -alkyl dithiocarbamates, 296 organophosphorus derivatives 87.4a–c (under aerated conditions in the presence of phosphine oxides as the coupling partner, Scheme 87b), 297 polysubstituted nitrogen-based heterocycles 298,299 and 1,3-diketones. 298…”

A Combination of Computational and Experimental Studies to Correlate Electronic Structure and Reactivity of Donor–Acceptor Singlet Carbenes

“…39 45 Also in a number of recent reports, it has been shown that during the reaction with a cyclic ether the lone pair at O attacks the carbene to generate an oxonium ylide followed by a nucleophilic attack to the resulting ylide for further transformation. 46 47 48 49 50 51 52 53 54 55 56 57 58…”

“…39,45 Also in a number of recent reports, it has been shown that during the reaction with a cyclic ether the lone pair at O attacks the carbene to generate an oxonium ylide followed by a nucleophilic attack to the resulting ylide for further transformation. [46][47][48][49][50][51][52][53][54][55][56][57][58] In this context there are some failed reactions where the underlying reason for the failure was not well understood. For example, Koenigs et al and we had reported amino etherification reactions of aryl diazo esters with NFSI in ethereal solvents.…”

Photochemical and Electrochemical Synthesis of Oxazoles and Isoxazoles: An Update

“…[13][14][15][16][17][18] Therefore, synthesis of these two crucial heterocyclic compounds using various green and sustainable methodologies has garnered significant enthusiasm within the community of synthetic organic chemists. [19] In this regard, photochemical [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] and electrochemical [38][39][40][41][42][43][44][45][46][47][48][49][50] techniques are considered as one of the most energy-efficient and environment-friendly approaches as they use photon or electron as activators and do not produce harmful waste. In recent years, extensive research has been done on photochemical and electrochemical synthesis of oxazoles.…”