Chemistry of acetylenic ethers XLII: A simplified method for the preparation of acetylenic thioethers; a number of new reactions of these compounds

Abstract

Cis ethenylene-1 ,Zbis-thioethers RSCH = CHSR can easily be prepared in liquid ammonia by treating cis or tvans 1,Zdichloroethylene with sodium amide and thiol.From these compounds acetylene thioethers HC =CSR can be obtained by means of sodium amide in liquid ammonia, followed by treatment with one mole of alkyl halide. If two moles of alkyl halide R'X are used, the alkyne thioethers R'C=CSR are formed in satisfactory yield.(Alky1thio)ethynylcarbinols R'R"C(0H)C =CSR are the products of treatment of ethenylene-1,2-bis-thioethers with sodium amide and ketones R'R"C=O in liquid ammonia.Addition of hydrogen chloride to (ethy1thio)ethyne gives l-ethylthio-1 -chloroethylene.Reaction of (ethy1thio)ethyne with acetone under the influence of boron fluoride produces a 50% yield of ethanethiol p,p-dimethylacrylate; similarly 1 -ethylthio-1 -propyne and acetone form ethanethiol a,p,p-tnmethylacrylate.The Mannich reaction of (ethy1thio)ethyne with formaldehyde and diethylamine gives (CzH5)zNCHzC =CSCzHs in very high yield.Long heating of (ethy1thio)ethyne at 90-100" causes the formation of 2-(ethy1thio)thiophene with much tar.Acetylene thioethers HC =CSR' have been obtained in various ways. In this paper we mention only one method, which is of interest in the present context ; for all the other methods we refer to a summary which is shortly to be published 1. 1

Copper and Silver Catalysis in the (3 + 2) Cycloaddition of Neutral Three-Atom Components with Terminal Alkynes

“…A third effect by mild acids can be hypothesized when considering the mechanism generally proposed for CuAAC, which features a metallacycle of type (11) as a key intermediate in the cycloaddition process (Figure 4B). Notably, the ratelimiting step of the cyclization portion in this mechanism is the formation of the first C−N bond, 28−30 which results in a lone pair of electrons being stabilized on the central nitrogen atom of the azide moiety.…”

The Synthetic Potential of Thiophenium Ylide Cycloadducts

“…2 This large limitation can be lifted with the use of "neutral" three-atom components (TACs) 8 capable of (3+2) cycloaddition. The use of neutral TACs is rare, [9][10][11][12][13][14][15][16][17][18][19] but these underexplored chemical entities present great potential for generating synthetic diversity towards heterocyclic structures. While classical 1,3-dipoles 2 produce stable, neutral cycloadducts 3, neutral TACs 4 produce unstable, zwitterionic cycloadducts 5.…”

“…24,25 To date, the (3+2) cycloaddition between alkynyl sulfides 8 and alkynes 1 has not been addressed. Other than the recent work on ynamides, 20,21 the literature on heteroatomsubstituted alkynes as TACs is limited to the pyrolysis of neat compounds 17 or the use of highly reactive benzynes as 2-atom cycloaddition partners, [18][19] which both impose great limits on functional group tolerance and structural diversity. With the prediction that alkynyl sulfides and alkynes may produce thiophenium ylides upon heating, ynetethered alkynyl sulfides presented a great platform for studying a variety of S-substituted thiophenium ylides.…”

The Synthetic Potential of Thiophenium Ylide Cycloadducts

“…2 This large limitation can be lifted with the use of "neutral" three-atom components (TACs) 8 capable of (3+2) cycloaddition. The use of neutral TACs is rare, [9][10][11][12][13][14][15][16][17][18][19] but these underexplored chemical entities present great potential for generating synthetic diversity towards heterocyclic structures. While classical 1,3-dipoles 2 produce stable, neutral cycloadducts 3, neutral TACs 4 produce unstable, zwitterionic cycloadducts 5.…”

“…24,25 To date, the (3+2) cycloaddition between alkynyl sulfides 8 and alkynes 1 has not been addressed. Other than the recent work on ynamides, 20,21 the literature on heteroatomsubstituted alkynes as TACs is limited to the pyrolysis of neat compounds 17 or the use of highly reactive benzynes as 2-atom cycloaddition partners, 18,19 which both impose great limits on functional group tolerance and structural diversity. With the prediction that alkynyl sulfides and alkynes may produce thiophenium ylides upon heating, ynetethered alkynyl sulfides presented a great platform for studying a variety of S-substituted thiophenium ylides.…”