Dimethyl dithioacetal, preparation

Formaldehyde dimethyl dithioacetal 5-oxide (FAMSO 113) and its ethyl analog are widely used as synthetic carbonyl equivalents. - Addition of the lithio derivative of (113) to aldehydes and ketones followed by acidic hydrolysis is a preparative method for a-hydroxy aldehyde derivatives (equation 27). A chiral analog of (113), (5)-formaldehyde di-p-tolyl dithioacetal 5-oxide (114), can be synthesized from (-)-mentyl (/ )-p-toluenesulfinate. °° The reaction of the lithio derivative of (5)-(114)... 

Dimethyl phosphite has been added to glycosulose derivatives (for example, 218) as a means of preparing C-phosphono sugars.474 Methyl 2,3,6-tri-0-benzoyl-a-D-n 6o-hexopyranosid-4-ulose reacts with 1,2-ethanedithiol to form the corresponding 4,4-ethylene dithioacetal.475... 

Further adaptations of the boranes has led to reagents which reduce carboxylic acids but afford thio-acetals rather than the aldehyde itself.Thus, with the thioborane (3 equation 1), aliphatic acids give 80-87% yields of thioacetals but aromatic acids respond less well in giving significant quantities of sulfides as well. Carboxylic acid esters are inert to this reagent but give sulfides if a Lewis acid is included. Similarly, the 1,3,2-dithiaborinane-dimethyl sulfide adduct (4 equation 2) affords cyclic dithioacetals in 70-90% isolated yields in the presence of SnCb. Aliphatic acids react in about 6 h at room temperature but aromatic acids need about 20 h and yields are somewhat poorer. This area has been reviewed.From a practical viewpoint, it should be noted that the dithiaborinane (4) requires a week for its preparation. 

Dithioacetals, 1,3-dithianes or 13-dithiolanes are prepared by reaction of the corresponding carbonyl compound in the presence of an acid catalyst (cone. HQ, Lewis acids such as Znh, BFs EtaO, TMS-Cl, etc.) with a thiol or dithiol. Silica gel treated with thionyl chloride was found to be an effective as well as selective catalyst for thioacetalization of aldehydes. Thioacetalization can also be achieved using a (polystyryl)diphenylphosphine-4odine complex as a catalyst Conversion of aldehydes or acetals into 1,3-dithianes is achieved with the aid of organotin thioalkoxides and organotin triflates or with 2,2-di-methyl-2-sila-l,3-dithiane. Direct conversion of carboxylic acids to 1,3-dithianes can be carried out by reaction with 1,3,2-dithiabomenane-dimethyl sulfide and tin(II) chloride or 1,3,2-dithiaborolene with trichloromethyllithium followed by basic hydrolysis. 

---