Silyl thione

In an extension of this method, >-haloacylsilanes were transformed by H2S/HCI into the corresponding silyl thiones, which underwent enethiolization on base treatment and subsequent intramolecular cyclization to afford a range of cyclic sulfides251. 

Sodium cuprate yielded less reduction product and less thiophilic addition product than lithium cuprate at both —50 and 0 °C. In the case of silyl thiones chiral at silicon, the reactions with organolithium derivatives and Grignard reagents produce a-silylsulfides with medium to good levels of asymmetric induction and, interestingly, the asymmetry induced at the a-carbon is retained in the subsequent desilylation431 (equation 118), the process being stereoselective. 

Chiral silyl thione 1, with the chirality located on the silicon atom, reacts with butadiene (2) to yield a mixture of two diastereomers 3 with a d.r. 75 25. Protodesilylation of the adduct leads to dihydrothiopyran, but an important drawback to this system is racemization of the chiral auxiliary during the protodesilylation process61. 

N-benzyladamantyl-2-imines, and 2-methyleneadamantanes were studied (352, 353). In particular, X-ray single-crystal analysis confirmed the configuration of the oxathiazoline 185, resulting from the favored attack of nitrile oxide on the 5-fluoroadamantane-2-thione. 2-Silyl-substituted oxathiazole 186 was synthesized by the 1,3-dipolar cycloaddition reaction of phenyl triphenylsilyl thioketone with 4-chlorobenzonitrile oxide (354). 

N-Alkylation is promoted by prior conversion of the pyrimidinones into their respective silyl ethers. Besides selectivity in the alkylation reactions, silylation confers solubility on molecules which otherwise may be difficult to dissolve in nonhydroxylic organic solvents. Selective N-3-alkylation of uracils requires initial protection of N-1. The alkylation of tautomeric thiones invariably proceeds to give an A-alkyl derivative any N-, 0-, or C-alkylation is less rapid and can be avoided. 

Reactions of enamines with monoimines of o-quinones afford polycylic compounds 228 with an oxazine ring (86MI2).Trifluoroacetylation of enamines with trifluoroacetic acid takes place in the /3-position of the enamine. Ketones (229) thus formed in an acidic medium afford fused 1,3-oxazines (230) (82JOC3339). Treatment of amines with silyl isothiocyanate gives not only pyrimidine derivatives but also l,3-oxazine-4-thiones (231) (81CCC2696). 

Silyl thioketones act as synthetic equivalents of thioaldehydes by protodesilylation with TBAF249,250, as shown in equation 23 (Section in.C.l). A related reaction is the heterocycloaddition of thiones with vinyltrimethylsilylketone, behaving as heterodiene474, to afford 4//-l,3-oxathiins as shown in equation 139. 

An unusual ring expansion of the pyrrolidin-2-one 305 has been reported to afford the azepine-2-thione derivative 307 on reaction with the bis silyl-substituted thioketene 304 (Equation 44) <1996CC1621>. It is probable that the... 

Long reaction times lead to the disappearance of the blue color of thione 1, related to the addition of a second molecule of hydrogen sulfide to give colorless gem-dithiols 3. Aromatic derivatives (R = Ar) are less prone to further addition of hydrogen sulfide, whereas with aliphatic derivatives (R = alkyl), gem-dithiols are generally the final reaction products and can be isolated and fully characterized.18 gem-Dithiols 3 can be converted into thioacylsilanes 1 by neutralization of the thionation solution with solid sodium hydrogen carbonate. With this procedure, enolizable acylsilanes 2 (R = R CH2) are stereoselectively transformed into Z-a-silyl enethiols 4 (vide infra). 

Indol-3-yl)-2,3-dihydro-l,2,4-triazine-3-thione was prepared, its X-ray structure determined, and used for the preparation of fused triazolo- and tetrazolotriazines <05RJO875>. Silyl substituted l,2,4-triazin-5-ones have been obtained from a-silyl-a-keto esters and thiosemicarbazide <05TL4049>. 

Perbenzylated pyranosyl trifluoro- and trichloracetates have been linked with silylated bases in the presence of SnCU, whilst condensation of pyridine-2-thiones with acetobromoglucose and -galactose has been used to make l-(P-D-glya yrano l)pyridinethiones... 

In the reaction of 3-(dialkylamino)-2//-azirines with trimethylsilyl isothiocyanate the initially formed [2+2] cycloadduct 59 again is transformed into the five-membered ring compound 60, which on treatment with methanol to remove the silyl group is converted into 4-(dialkylamino)imidazoline-2-thiones 61 (yield 26-80... 

Rodinovskaya LA, Shestopalov AM, Gromova AV, Shestopalov AA (2008) One-Pot synthesis of diverse 4-Di(tri)fluoromethyl-3-cyanopyridine-2(lH)-thiones and their utilities in the cascade synthesis of annulated heterocycles. J Comb Chem 10(2) 313-322 Suzuki H, Sakai N, Jwahara R, Fujiwa T, Satoh M, Kakehi A, Konakahara T (2007) Novel synthesis of 7-fluoro-8-(trifluoromethyl)-lH-l,6-naphthyridin-4-one derivatives intermo-lecular cyclization of an N-silyl-l-azaallyl anion with perfluoroalkene and subsequent intramolecular skeletal transformation of the resulting pentasubstituted pyridines. J Org Chem 72(15) 5878-5881... 

Isothiocyanatoacrylic esters R R C=C(C02Et)NCS are formed from a-isothiocyanato-acetates and -ketones via oxazoUdinc-2-thione anions in the presence of a base, and 2-siloxyalkyl or 2-siloxyphenyl isothiocyanates are formed thermally from N-silylated oxazolidine-2-thiones. ... 

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