Diphenyl thioacetals

The organotitanium compounds produced by desulfurization of the diphenyl thioacetals of aldehydes 28 with the titanocene(II) species Cp2Ti[P(OEt)3]2 29 react with carbon—carbon double bonds to form the olefin metathesis-type products. Thioacetals 28 may be transformed into terminal olefins by desulfurization with 29 under an ethene atmosphere (Scheme 14.15) [27]. This reaction is believed to proceed through a titanacyclobutane intermediate, formed by cycloaddition of the titanocene-alkylidene with ethene. 

Nitrogen heterocycles can also be prepared by the RCM of unsaturated amines having a diphenyl thioacetal moiety (Table 14.3) [31]. 

Treatment of diphenyl thioacetals 358 with the low-valent titanium Cp2Ti[P(OEt)3l2 produces 2,3-dihydrothio-phenes 360 together with 2-alkylidenetetrahydrothiophenes 361. The formers are formed by intramolecular olefina-tion of the titanium-carbene intermediates 359 (Scheme 62) <1999SL1029>. 

Thioacetalization. Aldehydes are converted into diphenyl thioacetals by reaction with diphenyl disulfide and tri-n-butylphosphine at room temperature for a few minutes (equation 1). Yields of thioacetals are much lower when triphenylphosphine is used and also when diphenyl disulfide is replaced by dialkyl disulfides. Ketones are not reactive to this system even under forcing conditions. 

Vinyl phenyl sulfides. Treatment of diphenyl thioacetals and thioketals with this soluble Cu(l) salt induces elimination of thiophenol at 25° ... 

KETONES f-Butyl a-lithioisobutyrate. Benzoin. Chlorocarbonylbis(triphenylphosphine)-rhodium(I). m-Chloroperbenzoic acid. Chromic acid. Dimethylcopperlithium. Diphenyl disulfide. Formaldehyde diphenyl thioacetal. Methylthioacetic acid. Sodium cyanide. Tetrakis triphenylphosphine)palladium(0). Trimethylchlorosilane. Triphenyl-methyl isocyanide. Trimethylsilyl cyanide. 

Diphenylsulfilimines, 239 Diphenyl sulfoxide, 241 Diphenyl thioacetals, 130 Diphenyl thioketals, 130... 

Fluorovinyl methyl ketone, 263 Fluoroxytrifluoromefhane, 263-264 Formaldehyde, 18, 264-267, 379, 590 Formaldehyde diphenyl thioacetal, 267 Formamidincsulfinic acid, 586 Formic acid, 597... 

Formaldehyde diphenyl thioacetal (Bis(phenylthio)methane], H2C(SC6H5)2. 

Heptanal diphenyl thioacetal treated at -40 to -30 under argon with n-butyl-lithium in tetrahydrofuran during 1 hr., 0.5 equivalent Cul added at once at -78°, stirred 1 hr., a soln. of methyl vinyl ketone in tetrahydrofuran added dropwise, and stirred 2 hrs. at -78° -> y-ketothioketal (Y 80%) treated with 2 equivalents CuClg and 4 equivalents CuO in aq. 99%-acetone -> undecane-2,5-dione (Y 90%). F. y-diketones from y-ketomercaptals s. T. Mukaiyama, K. Narasaka, and M. Furusato, Am. Soc. 94, 8641 (1972). 

As described in the previous section, a-elimination of dialkyltitanocenes is of limited use for the preparation of titanocene-alkylidenes. Since thioacetals are readily available from carbonyl compounds or through alkylation of bis(phenylthio)methane and related organosulfur compounds, a thioacetal-titanocene(II) system enables the use of different types of carbene complexes. Use of appropriate thioacetals is of crucial importance in this system for the preparation of alkylidene complexes 48, the corresponding diphenyl thioacetals are the starting materials of choice. No carbene complexes are formed from dialkylthio-acetals. To generate vinylcarbene complexes 49, trimethylene thioacetals of aji-unsaturated aldehydes or l,3-bis(phenylthio)propene derivatives are employed (Scheme 4.41). The low-valent titanium species 44 is also easily prepared by the reduction of titanocene dichloride with magnesium in the presence of triethyl phosphite at room temperature. The presence of molecular sieves 4A is essential for the reproducibility of this preparation. In relatively large-scale preparations, care should be taken to control the reaction temperature [92, 93g]. 

---