[534-18-9] · CNa2S3 · Sodium Trithiocarbonate · (MW 154.20)
(converts alkyl chlorides into thiols;1 1,2- or 1,3-dihaloalkanes or dimesylates into cyclic trithiocarbonates2 or into alkenes;3 reductively removes chloroethyl ester protecting groups;4 effective for demercuration5)
Preparative Method: a 33% aqueous solution is prepared from Sodium Sulfide and Carbon Disulfide in H2O.
Alkyl chlorides can be treated with sodium trithiocarbonate followed by an acidic workup to prepare the corresponding thiol (eq 1).1a This methodology was applicable to simple alkyl chlorides (eq 2)1b and to b-alkoxy chlorides (eq 3).1a It was noted that this method was superior to direct substitution with NH4SH.
Sodium trithiocarbonate can be reacted with Chloroacetonitrile with liberation of carbon disulfide (eq 4).6 The mercaptoacetonitrile could be reacted further with acid chlorides, providing cyanomethyl thioesters.
Thioureas have been prepared by reaction of sodium trithiocarbonate, 2-Chloro-1-methylpyridinium Iodide and two equivalents of the appropriate amine.7 The bis(pyridinium) thiocarbonate intermediate is activated toward nucleophilic attack (eq 5). The authors point out that other methods suffer from severe conditions and toxic reagents (e.g. Thiophosgene). Sterically hindered amines, such as 2,6-dimethylaniline, were accommodated as well.
Chloroethyl esters, when treated with sodium trithiocarbonate, are reductively deprotected to liberate the carboxylic acid.4
Cyclic trithiocarbonates are important intermediates en route to insecticides and other biologically active compounds.8 These compounds can be synthesized by a double nucleophilic addition of sodium trithiocarbonate and 1,2- or 1,3-bis(mesylates)2a or halides (eqs 6 and 7).2b It was found that the reactions of the dibromide compounds were best performed under phase-transfer catalysis with trioctylmethylammonium chloride. In general, the yields were better for five-membered ring formation than for six-membered rings. One limitation for five-membered rings was that R1 and R2 need be alkyl groups. When R1 and R2 were phenyl or methoxycarbonyl groups, alkenes were isolated in excellent yields by a single electron transfer mechanism.3
Cyclic trithiocarbonates have been selectively reduced to the dithiol or the thioacetal depending on the choice of reducing agent (eq 8).9 Thus reduction with Lithium Aluminum Hydride in toluene at 110 °C provided good yields of the dithiol whereas if Diisobutylaluminum Hydride was employed, the thioacetal was isolated. The trithiocarbonate could also be desulfurized with aqueous Mercury(II) Acetate to provide the 1,3-dithiole-2-thione (eq 9).10
A synthetic sequence en route to propionate natural products utilized the regio- and stereoselective oxymercuration11 of stereodefined enoates. The success of this method hinged upon the stereoselective removal of mercury (eq 10).5 Previous methods (e.g. Sodium Borohydride and Sodium Sulfide)12 gave poor diastereomeric ratios. In this system it was determined that sodium borohydride favored formation of the threo isomer and the dithiol reagents gave preferentially the erythro product. Sodium trithiocarbonate was slightly less efficient than 1,3-Propanedithiol both in terms of yield and selectivity.
Jonathan R. Young
University of Wisconsin-Madison, WI, USA