Metal‐ and Catalyst‐Free One‐Pot Cascade Coupling of α‐Enolic Dithioesters with in situ Generated 4‐Chloro‐3‐formylcoumarin: Access to Thioxothiopyrano[3,2‐c]chromen‐5(2H)‐ones

Abstract

An efficient and viable one-pot protocol for the synthesis of a specific class of 2-thioxothiopyrano[3,2-c] chromen-5(2H)-ones has been devised by the cross-coupling of 4-hydroxycoumarin and αenolic dithioesters under metal-and additive-free conditions in open air. The reaction proceeds via in situ generation of 4-chloro-3-formylcoumarin followed by consecutive Michael-type addition/ intramolecular cyclization/ elimination cascade, enabling the creation of thiopyran-2-thione ring over coumarin framework through successive formation of CÀ C and CÀ S bonds. Remarkably, the benign conditions, atom-economy, and quantifying forbearance of a wide horizon of functional groups are added characteristics to this strategy.

Regio- and Chemoselective Access to Dihydrothiophenes and Thiophenes via Halogenation/Intramolecular C(sp2)–H Thienation of α-Allyl Dithioesters at Room Temperature

“…Isolated yield: 62 mg (95%); sticky yellow solid; 1 H NMR (500 MHz, CDCl 3 ) δ 7.66 (d, J = 7.8 Hz, 2H), 7.23 (s, 2H), 6.89 (s, 1H), 2.54 (s, 3H), 2.42 (s, 3H), 2.40 (s, 3H); 13 C{ 1 H} NMR (125 MHz, CDCl 3 ) δ 189. 8,149.3,142.5,136.7,136.5,135.5,130.9,129.3,128.9,128.2,21.6,19.3,(5-methyl-2-(methylthio)thiophen-3-yl)methanone (4c). Purified by silica gel column chromatography eluted with 5% ethyl acetate in 95% hexane.…”

“…(5-Methyl-2-(methylthio)thiophen-3-yl) (3,4, 8,152.6,152.0 (d,J = 9.3 Hz),150.0,149.9,137.0,133.1,127.3,19.1,15.4; HRMS (ESI-TOF, [M + H] + ) calcd for C 13 H 10 F 3 OS 2 303.0120, found 303.0115.…”

“…Over the past few years, the remarkable renovation of a simple synthon α-enolic dithioester has been achieved toward the synthesis of diverse sulfur-containing heterocycles. 8 Recently, we found that α-allylated dithioesters (ADTEs), which can be conveniently prepared from readily available dithioesters, could be used for the construction of sulfur heterocycles. 9 Encouraged by the success of our continuous efforts, we became interested in further expanding the synthetic utility of α-allylated dithioesters.…”

Unusual Behavior of Ketoximes: Reagentless Photochemical Pathway to Alkynyl Sulfides

“…The β-oxodithioester moiety has been immensely explored by our group and others in the past decade − for the synthesis of five- and six-membered functionalized heterocycles. Photocatalysis has been established as a green, energy-efficient process for organic transformations, but direct access to functionalized alkynes is rare and we became interested in developing synthetic cores which come out clean on the pot-atom-step economy parameters .…”

Synthesis of 1,3,4-Thiadiazoles and 1,4,2-Oxathiazoles from α-Enolic Dithioesters and Active 1,3-Dipoles

“…2 Among the latter, α-enolic dithioesters A have been proven to be a class of useful and versatile synthons, and their synthetic applications have been extensively studied to access various sulfur-containing heterocyclic compounds (e.g., thiopyrans, 3b isothiazoles, 3c and thiazoles 3d ) in the past decades. 3 Continuing our ongoing interest in sulfur-containing building block, 3g,4 we were also attracted to α-enolic dithioesters, because α-enolic dithioesters, structurally, possess two electrophilic and three nucleophilic reactive sites and could react with suitable reaction partners in a regioselective manner (Scheme 1). For example, Junjappa reported a cyclocondensation reaction of arylhydrazines with α-enolic dithioesters to afford substituted pyrazoles using two electrophilic sites (CO and CS, eq a).…”