Ethylthio radical

It is important to emphasize that the hydroxy dithioketal cyclization can be conducted under mild reaction conditions and can be successfully applied to a variety of substrates.15 However, the utility of this method for the synthesis of didehydrooxocane-contain-ing natural products requires the diastereoselective, reductive removal of the ethylthio group. Gratifyingly, treatment of 13 with triphenyltin hydride and a catalytic amount of the radical initiator, azobisisobutyronitrile (AIBN), accomplishes a homolytic cleavage of the C-S bond and furnishes didehydrooxocane 14 in diastereo-merically pure form (95 % yield), after hydrogen atom transfer. 

Fig. 3 a, b. Experimental ESR spectrum of the radical produced by the heating of methyl a-ethylthio-acrylate at 85 °C (a), and simulated ESR spectrum of the radical —CH2C (SEt)COOMe (b)... 

A further interesting feature of the polymeric photoinitiators is based on the possibility of anchoring different photosensitive moieties to the same macromolecule in order to provide a synergistic effect on activity due to their interaction along the polymer chain. In this context, the synthesis of several copoly-meric photoinitiators bearing side-chain thioxanthone and hydroxyalkylphenone or morpholino ketone moieties has been reported recently [156]. In particular, the free radical copolymerization of 2-[2-(acryloyloxy)ethylthio] thioxanthone (AETX) with either [4-(2-acryloyloxyethoxy)phenyl]-2-hydroxy-2-propyl ketone (HPA) or [4-(2-acryloyloxyethylthio)phenyl]-2-(iV-morpholino)-2-propyl ketone (APMK) [poly(AETX-co-HPA) and poly(AETX-co-APMK), respectively] and of 4-[2-(methacryloyloxy)ethoxycarbonyl] thioxanthone (METX) with APMK [poly(METX-co-APMK)] has been performed. 

Table 3. Mulliken spin population distributions for unsubstituted (Tyrosyl) and ethylthio-substituted (Tyrosyl-S) tyrosyl radicals calculated with various DFT-fiinctionals.

Ethylation of l,2-dithiole-3-thione gives a 3-ethylthio-l,2-dithiolylium ion whose electroreductive dimerization has been investigated. A series of aryl-substituted l,2-dithiol-3-ylidene acetophenones underwent oxidative dimerization via cation-radicals (142) when electrolyzed the dimeric products, which contain a new C—C bond, were elaborated chemically into a series of highly conjugated derivatives including bithiathiophthenes. " ... 

This conception works out as shown in Scheme 10 CTP 23 formed by the above described sequence is directly consumed by -acetyl neuraminic acid 26 under the catalytic influence of cytidine-5 -monophosphosialate synthase (E.C. 2.7.7.43). This enzyme is isolated from calf brain by ammonium sulfate precipitation (2 5) and subsequent affinity chromatography. The stationary phase consists of CNBr-activated Sepharose 4B reacted with p-[3-(2-amino ethylthio)propyl]-iV-acetyl neuraminic acid 27, which is synthesized by radiating a mixture of the allyl glycoside and cysteamine to achieve radical C-S bond formation (24), The behavior of methyl p-N-acetyl-neuraminic acid as an inhibitor is in accordance with Zbiral s findings (25), where the methyl a-glycoside has been shown to compete with the native substrate for the enzyme, and thus 27 is recommended to be an ideally suited ligand (Scheme 9). A typical analytical run is shown in Scheme 9. Due to elution of the protein fraction by a salt gradient, the transfer to a preparative scale is rather difEcult denaturation occurs and thus a drop in activity down to 6% is observed. 

For example, mesoionic 2-[2-(isopropenylcarbonyloxy)ethylthio]-l-methyl-6-oxo-3-phenyl-5-propyl-l,6-dihydro-pyrimidin-3-ium-4-olate (11) (34) was stirred in equimolar amoimt with a solution of RAMEB for 5 days at ambient temperature. The 2 1 hosfc-guest complex 11/RAMEB was isolated in 71% srield relative to the guest monomer. The water solubility of complex was about 800 mg in 1-ml water at ambient temperature. The radical polymerization of RAMEB-complexed monomer was carried out with 3.3 mol% of redox initiator potassiiun peroxodisul-fate and sodium hydrogensulfite. According to the results of the gel-permeation chromatography (GPC) obtained for the polymer prepared from the imcomplexed monomer, 85% of 11 was unreacted after 1 h. Additionally, the molecular weight distribution of the polymer synthesized without RAMEB is bimodal with = 11,000 g/mol and polydispersity of 4.5 (35). 

Reactions at acid centers to create 5 -2-(trimethylsilyl) ethanethiolesters are also common. Carboxylic 5-thiolesters are formed in high yield by the DCC/DMAP mediated coupling of 2-(trimethylsilyl)ethanethiol and carboxylic acids or by thiol substitution on a carboxylic acid chloride. 5 -2-(Tiimethylsilyl) ethyl p-toluenethiolsulfonate is formed by treating 2-(trimethyl-silyl)ethanethiol with tosyl bromide (eq 4). The product is a useful electrophile for carbon nucleophiles, allowing the introduction of the 2-(trimethylsilyl)ethylthio unit by an alternative mechanism. Independent of the thiol, aryl and alkyl 2-trimethylsilylethyl thioethers may be prepared by the radical addition of the appropriate arene- or aikanethiol to vinyl trimethyl-silane in a reaction comparable to that of eq l7 ... 

The kinetically controlled radical addition of ethyl mercaptan to ethoxy-acetylene is also trans and sterospecific at low conversions to give cw-l-ethoxy-2-(ethylthio)ethylene (103)7 ... 

Radical reactions feature in a number of related systems. The photochemical decomposition of aromatic azides in the presence of ethanethiol results not in the usual ring expansion to 2-substituted-3//-azepines but in the formation of thioethoxy-compounds. Phenyl azide gives 2-ethylthio-l-aminobenzene (190), which is the result of a 1,2-nitrogen walk by the azide a-N (Scheme 29) demonstrated in the corresponding reaction of p-toyl azide. 

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