Visible-light initiated oxidative cyclization of phenyl propiolates with sulfinic acids to coumarin derivatives under metal-free conditions

Abstract

A visible-light initiated oxidative cyclization of phenyl propiolates with sulfinic acids has been developed. The arylsulfonylation of alkynes was performed at room temperature under metal-free conditions to generate coumarin derivatives with wide functional group tolerance, good yields and high regioselectivity.

Generation of Sulfonyl Radicals from Aryldiazonium Tetrafluoroborates and Sulfur Dioxide: The Synthesis of 3‐Sulfonated Coumarins

“…Ethene-1,1,2-triyltribenzene (8) and (2-(phenylsulfonyl)ethene-1,1-diyl)dibenzene (9) were observed in 11 and 25 % yields, respectively, thus indicating the existence of both aryl radical and sulfonyl radical in this reaction. Only the cyclized product 6 was produced in 52 % yield, whereas the normal product could not be detected (Scheme 3 a).…”

“…[1][2][3][4] Notably, the generation of a sulfonyl radical and its addition to unsaturated CÀC bonds (such as alkenes and alkynes) contribute much to recent advances in the synthesis of sulfones. [6,7] The single-electron oxidation of sulfinates [8] or sulfinic acids [9] and the oxidative cleavage of sulfonyl hydrazides [10] also provide efficient routes for the formation of sulfonyl radicals (Scheme 1 b). [5,6] For instance, sulfonyl radicals can be produced from their corresponding sulfonyl halides, sulfonyl selenides, sulfonyl azides, and sulfonyl cyanides in the presence of radical initiators, light, or catalysts (Scheme 1 a).…”

Photokatalyse mit sichtbarem Licht: Welche Bedeutung hat sie für die organische Synthese?

“…Der radikalische Reaktionsverlauf wurde durch den Nachweis des TEMPO-Addukts 131 unterstützt (Schema 35 a). [126] Aromatische Sulfoxideinheiten sind ein Strukturelement in Naturstoffen, [127] Herbiziden, [128] Arzneistoffen [129] und Hochleistungsmaterialien. [125] Mit einem ähnlichen photokatalytischen System entwickelte Wang eine Difunktionalisierung von Alkinen (siehe SI, Schema S9).…”

Organic Reactions Promoted by Metal-Free Organic Dyes Under Visible Light Irradiation

“…The reaction of 1,2-dihydronaphthalene 6 with sodium benzenesulfinate 5 was performed in the presence of EY (10 mol%) and nitrobenzene as a terminal oxidant (Figure 3). The oxidative cyclization reaction between 3-phenylpropiolate 8 and 4-methylbenzenesulfinic acid 9 was studied (Figure 4) [22]. In the presence of EY (1 mol%) and tert-butyl hydroperoxide (TBHP), the reaction between 8 and 9 was performed in MeCN-H 2 O (1:1, v/v) under the tert-butoxyl radical is produced by the single-electron transfer from the excited EY (EY*) to TBHP.…”

“…Eosin Y (EY) is the typical organic dye to induce the synthetically useful photoredox transformations [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. EY that absorbed visible light populates in the lowest excited singlet state.…”