Methyl dithioacetate

The possibility of conversion of the dithioacctal into the corresponding ketone without reconjugation of the double bond is a noteworthy j feature of this synthetic scheme. The syntheses of iso-ar-turmerone and isoartemisia ketone mentioned above proceeded similarly via a carbophilic pathway. In the latter case a p-ethylenic dithioester was not isomerized during the following overall sequence carbophilic addition-methylation-dithioacetalization [343]. ... 

With a,p-disubstituted enuiies an unexpected mode of stereocontrol was evidenced [365, 366]. Syn products (7) were obtained by addition of the lithium enethiolate of methyl dithioacetate to an a,3-disubstituted enone via diastereoselective auto-protonation of the intermediate enolate generated in the 1,4 addition. 

To a solution of LDA (40mmol) in THF (200ml) cooled at -45°C, methyl dithioacetate (3.92 ml, 40 mmol) was added dropwise. The yellow colour rapidly disappeared. The mixture was stirred for 5 min. 2-Cyclohexenone (3.92 ml, 40 mmol) was then added dropwise. A yellow colour appeared. The resulting mixture was stirred for 15 min. An aqueous solution of ammonium chloride was added and the mixture partitioned between ether and brine. The organic layer was washed with brine, dried with magnesium sulfate and concentrated. Methyl (cyclohexanone-3-yl)dithioacetate (3) (6.75 g, 33.4 mmol, 83%) was isolated by flash chromatography on silica gel using cyclohexane/ethyl acetate (9 1) as the eluent. 

Metzner reports that lithium dithioenolates, which are softer nucleophiles than the corresponding carbonyl enolates, add kinetically in a 1,4-mode exclusively to ot, 3-enones and the diastereoselectivity preferences are similar to that for ester enolate additions.l43a d Typically, kinetic deprotonation of dithioesters affords predominantly the (Z)-enethiolate (170) which is opposite to that for esters 139 thus, with ( )-enones, anti adducts (172) are obtained. In contrast, the addition of methyl dithioacetate to ot,P-disubstituted enones affords predominantly syn adducts (174 and 175) which is a consequence of intramolecular protonation of the resultant enolate (Scheme 68).143e... 

Reaction of diazoalkanes with thiocarbonyl compounds, which may be considered an extension of Pechmann s synthesis, forms 1,2,3-thiadiazole derivatives (75SST(3)67o). For example, methyl dithioacetate reacts with diazomethane to form a mixture of thiadiazole isomers and thiirane the latter often is the main product of this type of reaction (equation 26). O-Ethyl thionoacetate reacts with ethyl diazoacetate to form a substituted thiadiazole (equation 27). However, an aryl thionoester reacts with diazomethane to yield a 1,2,3-thiadiazole derivative which is only formed as an intermediate (31) and then rapidly decomposes to alkene (Scheme 5). 

N, P] Mukaiyama and co-workers explored the addition of methyl dithioacetate to enones under the influence of tin(II) triflate, a chiral, nonracemic diamine (34.1-34.4), and trimethylsilyl triflate (Scheme 34,... 

Methyl Dithioacetate to a,/J-Unsaturated Ketones in the Presence of Chiral, Non-racemic Diamines (Scheme 34)... 

The normal Raman scattering process is improbable and gives rise to a weak Raman spectrum. However, there is a condition under which the spectrum can be greatly intensified, as a result of a phenomenon known as the resonance Raman (RR) effect. The Raman spectrum, obtained using an excitation wavelength of 488 nm, of the dithioester methyl dithioacetate is illustrated in Fig. 3. The spectrum has peaks which contain contributions from the stretching motions of the C-H, C = S and C-S bonds, i>c h. c=s c-s> respectively. This Raman spectrum, although... 

Asymmetric induction is also observed in the conjugate addition of the chiral acetone imines (32) to cycloalkenones to provide 3-acetonyl-cycloalkanones (33) in reasonable yields after lithiation and copper catalysis. Alternatively, the masked 1,5-dicarbonyl compounds (34) are obtained when lithium methyl dithioacetate (35) adds in a regioselective manner to cycloalkenones, although no stereoselectivity is observed. ... 

The action of diazoalkanes on thiocarbonyl compounds provides a versatile route to thiirans 1,2,3-thiadiazole derivatives, which function as intermediates, are isolable in suitable cases. Thus, diazomethane reacts with thionesters (1) yielding 5-alkoxy-5-methyl-A -l,2,3-thiadiazolines (2) (ca. 60%) together with the next higher homologous thionester (3) (ca. 30%). Aromatic members (2 R = Ar) decompose readily to the alkenes (5). Ethyl thioformate (1 R = H, R = Et) gives rise, by methylation and aromatiza-tion, to (4), and to linear products. Comparable observations involving diazoethane and diazopropane are also on record. The formulation of the products as 1,2,3-thiadiazolines (2) in preference to the possible A -1,3,4-thiadiazoline structures (6) is supported by the results of n.m.r. studies. However, both isomers, (8) (20%) and (9) (45%), are obtained when diazomethane acts on methyl dithioacetate (7) at —70 C (compare also these Reports, Vol. 1. p. 450). ... 

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