Dithiols from alkenes

To obtain ethylenedithiols, the main options described in Scheme 1 are available. Vicinal dithio-ethers, which can be prepared from cis-dichloro- or dibromo-alkenes or from alkenes through a stepwise synthesis, can be cleaved to produce dithiols (Route A). Ethylenedithiocarbonates can be prepared by several well-established procedures and by some less general ones as well. The ethylenedithiocarbonates are central intermediates for many dithiolene syntheses and for syntheses of derivatives of the electron donor tetrathiafulvalene (TTF), which has been intensively investigated in the past decade. This has widened the synthetic possibilities for ethylenedithio-carbonates. Their cleavage by alkali metal hydroxides or alkoxides produces salts of ethylenedithiolates (Route B). As an alternate route, their photolysis with loss of CO and generation of a dithioketone has been explored. ... 

This reaction is based on a stoichiometric reaction of multifunctional olefins (enes) with thiols. The addition reaction can be initiated thermally, pho-tochemically, and by electron beam and radical or ionic mechanism. Thiyl radicals can be generated by the reaction of an excited carbonyl compound (usually in its triplet state) with a thiol or via radicals, such as benzoyl radicals from a type I photoinitiator, reacting with the thiol. The thiyl radicals add to olefins, and this is the basis of the polymerization process. The addition of a dithiol to a diolefin yields linear polymer, higher-functionality thiols and alkenes form cross-linked systems. 

Synthesis of 1,3,2-dithiazoles has been the most extensively studied. Various structural types of these compounds have been synthesized in 1990s from raV-dithiols, bis(sulfenylchlorides), and alkynes <1996CHEC-II(4)433>. Much attention has been paid to the preparation of stable 1,3,2-dithiazolyl radicals and, especially, cations. The synthetic potential of 1,3,2-oxathiazoles and 1,3,2-dioxazoles is restricted by several uncommon procedures including nitrosation of thiolcarboxylic acids and photochemical addition of nitrobenzene to alkenes <1996CHEC-II(4)433>. 

The reactions of alkynes, alkynoic esters, ynamines, and dehydrobenzene with l,2-dithiole-3-thiones (2b), and occasionally l,2-dithiol-3-imines (12c), has been extensively studied <82AHC(3i)63>. The initial products for thiones are 3-thioacylmethylene-l,3-dithioles or thiazoles (111), which can react further to form di- or tri- adducts (113) and (114) respectively. Other rearrangements can give trithiapentalenes (6). Thials, formed from reactions of 5-unsubstituted-l,2-dithiole-3-thiones, can dimerize to products (112) with loss of sulfur (Scheme 14). Similar types of reactions have been observed with l,2-dithiole-3-thiones (2b) reacting with alkenes and ketenes, especially under... 

Sulfuranyl-alkyl biradical (43) constitutes a plausible intermediate in the (overall) photoextrusion of alkenes from naphtho [1, 8-, /] [1, 4] dithiepins (44) affording naphtho [1,8-c, J]-l,2-dithiole (45). The reaction (Scheme 16) proceeds from an excited singlet state of (44) and evidence for a transannular bonding interaction between the S atoms in (44) (and thus in the primarily formed biradical (46)) stems both from experimental results and theoretical calculations [38]. 

Thiol anhydrides (RCO)2S are formed on reaction of RC(S)OSiR3 with RC(0)C1, and the salts RCS2 R2NH2+ are oxidized to [RC(S)S]2 by RSO2CI. Coyle has reviewed the photochemical properties of thioesters. Compound (172) is split into PhC(0)SH and PhCMe=CHa on photolysis." Ethyl thiono-acetate yields a complex mixture of products on u.v. irradiation, from which 2,3-diethoxybut-2-ene and 2,3-diethoxybut-l-ene can be isolated. Photolysis of benzo-l,2-dithiole-3-thione in the presence of alkenes yields the blue compound (211). ... 

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