Thiocarbonylthio compounds

Abstract

(A) Thiocarbonylthiol compounds are more acidic and therefore undergoe β-eliminations under basic conditions. The efficient addition of xanthate to mesityl oxide in an acidic medium to avoid the reversible addition gives the product in 76% yield. Thus, tertiary derivatives can be accessed through a conjugate addition rather than by SN2 substitution. (figure presented) (B) The synthesis of tertiary xanthate by methylation of xanthate can be achieved by addition of an excess amount of the alkylating agent before adding the base. By inverting the mode of addition the ketene monothioketal can be obtained. (figure presented) (C) Secondary alcohols can be converted into the corresponding thiols using this method. This method is convenient in cases where a traditional ionic approach is difficult to use.4 The radical generated using carbon-centered radical by proper selection of the various substituents and the experimental conditions, scission of the CO bond is irreversible, and leads to an S,S′ dithiocarbonate. (figure presented) (D) If xanthate is separately exposed to the action of peroxide, then there is no alternative other than generating radical, even if it is not particularly stabilized. This radical may add to aromatic ring giving the stabilized cyclohexadienyl radical. The radical is easily oxidized to the equally stable corresponding cation by electron transfer to the peroxide. Aromatization by loss of proton quickly yields indoline. (figure presented) (E) For the generation and intramolecular capture of carbamoyl radicals, dithiocarbamates proved better than xanthates. The formation of the β-lactam from acyl dithiocarbamate via an acyl radical has been reported by Grainger and Innocenti. Lactams of various sizes were prepared by the same approach. (figure presented) (F) When xanthate is added to vinyl pivalate, a related adduct is formed which is further reacted with allyl cyanide. The expected adduct is not isolated but exposed to the action of a base, 1,8-diazabicyclo[ 5.4.0]undec-7-ene (DBU), which causes two successive b-eliminations leading to the diene. (figure presented) (G) Xanthates have been readily converted into ortho-chlorophenyl thioethers using a one-step procedure and radical conditions. In some cases, the aryl thioethers are successfully oxidized to the corresponding sulfoxides and sulfenic acid elimination afforded the corresponding vinylsilanes. (figure presented) (H) Various primary 2-aminothiols have been prepared in three steps starting from 2-aminoalcohols and methyldithioacetate. (figure presented) (I) The use of thiocarbonylthio compounds in radical polymerizations is a versatile method for conferring living characteristics providing unprecedented control over molecular weight, molecular weight distribution, composition, and architecture. It provides a route to functional, cyclo-, block, and star polymers as well as to gradient copolymers. © Georg Thieme Verlag Stuttgart New York.