[10152-75-7] · C3H4S · Methylthioacetylene · (MW 72.14)
Physical Data: bp 70 °C/760 mmHg; n
Solubility: sol organic solvents.
Form Supplied in: pale yellow to dark brown liquid.
Preparative Methods: by double elimination of HBr from the dibromide (obtained by bromination of methyl vinyl sulfide) (eqs 1 and 2).5 The preparation of methyl vinyl sulfide from commercially available methylthioethanol has been described.6 Methylthioacetylene has also been prepared by the reaction of sodium acetylide with sulfur followed by quenching of the resulting sulfide ion with methyl iodide.7a
Purification: distillation under nitrogen at atmospheric pressure.
Handling, Storage, and Precautions: should be used freshly distilled for best results (pale yellow). Since methylthioacetylene has limited thermal stability, distillation at normal pressure should be carried out (under N2) with relatively small amounts of material.
Functionalized methylthio-substituted alkynes can be prepared by deprotonation of methylthioacetylene and reaction of the resulting acetylide ion with an appropriate electrophile (eq 3).1 An interesting thio-Claisen substrate can be constructed in this fashion (eq 4).7b
Methylthioacetylene participates in an asymmetric [2 + 2] cycloaddition with a fumarate amide derivative catalyzed by a chiral TiIV alkoxide to furnish a methylthiocyclobutene (eq 5).2 Condensation of methylthioacetylene as the nucleophilic component with thiobenzoyl isocyanate provides a sulfur-containing heterocyclic structure (eq 6).3 Finally, addition of a [(trimethylsilyl)methyl]copper(I) reagent to methylthioacetylene produces a bifunctional allylic silane (eq 7)8 and condensation of methylthioacetylene as the electrophilic component with 2-(dialkylamino)arylacetonitriles gives rise to enamino allylic sulfides (eq 8).9
Regio- and stereoselective syntheses of functionalized methyl vinyl sulfides is accomplished by Pd0-catalyzed hydrostannation (eq 9)4a,b and carbocupration (eq 10)4c of 1-methylthio-1-alkynes. In turn, vinyl sulfides are very useful intermediates in organic synthesis, not only as carbonyl-masking moieties10 but also in a variety of other transformations11 including the Ni0-catalyzed cross-coupling reaction with Grignard reagents.12 1-Methylthio-1-alkynes can in principle be prepared by deprotonation of methylthioacetylene and subsequent reaction with an appropriate electrophile (e.g. eq 3).13 However, the 1-methylthio-1-alkynes shown in eq 9 and eq 10 were prepared by the reaction of a metal acetylide derivative with either S-methyl methylthiosulfonate or dimethyl disulfide.4b,14
Plato A. Magriotis
West Virginia University, Morgantown, WV, USA