Mercaptals bis

Addition of methyllithium to the lactone 1219, followed by reduction with sodium borohydride in refluxing ethanol, afforded, almost quantitatively, ellipticine (228). Reaction of the compound 1219 with the lithio derivative of formaldehyde diethylmercaptal, and reduction with sodium borohydride in refluxing ethanol, led to the mercaptal 1221. Cleavage of the mercaptal 1221 with bis(trifluoroacetoxy) iodobenzene [Phl(OCOCF3)2] in aqueous acetonitrile gave the 11-formyl derivative, which was reduced with sodium cyanoborohydride (NaBHsCN) to 12-hydroxyellipticine (232) (710,711) (Scheme 5.202). The same group also reported the synthesis of further pyiido[4,3-fc]carbazole derivatives by condensation of 2-substituted indoles with 3-acetylpyridine (712). 

BIS(ETHYLTHIO)METHYLENE)PROPANEDINITRlLE MALONONITRILE, CARBONYL-, DIETHYL MERCAPT-OLE PROPANEDINITRILE, (BIS(ETHYLTHIO)-METHYLENE)-... 

Mercaptals of pentoses and hexoses are converted into sulfonals (di-sulfones), which easily undergo dehydration. The dimethylmercaptal of D-ribose or D-arabinose gives, on oxidation with peroxypropionic acid, 1,1-bis(methylsulfonyl)-D-er> f/iro-pentos-l-ene (equation 571) [340. ... 

Reaction of thiols with aldehydes or ketones leads to formation of water and geminal bis(alkylthio) compounds, which, when derived from aldehydes, are known as mercaptals or, when derived from ketones, as mercaptols ... 

General preparation of mercaptals 90 Dry hydrogen chloride is led into a mixture of a thiol (2 moles) and an aldehyde (1 mole), reaction occurring in a short time with evolution of heat and separation of water. The solid mercaptal is recrystallized from ether, light petroleum, or benzene. The following are examples benzaldehyde bis-(p-bromophenyl) mercaptal, m.p. 79-80° (from ether) cinnamaldehyde diphenyl mercaptal, m.p. 80-81° (from light petroleum) piperonaldehyde diphenyl mercaptal, m.p. 48° (from acetone). 

To an ice cold solution of 20.0 g D-glucose diethyl mercaptal pentaacetate in 200 mL dry ether was added 35.21 g monoperphthalic acid in ether (4.8 eq.). The solution was cooled in ice for 1 h and then allowed to stand at room temperature for an additional 16 h. The ether was removed under reduced pressure, and the residue was extracted with CHCI3 (4 X 75 mL). The chloroform was washed with saturated aqueous NaHCOs and then with water and was dried over Na2S04. Then CHCI3 was removed under reduced pressure to give 19.9 g D-arabo-3,4,5,6-tetraacetoxy-l,l-bis-(ethanesulfonyl)-hexene-l as a crystalline material, m.p., 134-146°C. Two recrystallizations from diisobutyl ketone followed by one from isopropyl alcohol and one from methyl ethyl ketone by addition of petroleum ether (b.p. 35-60°C), gave 12.9 g pure product with a constant melting point of 160-162°C, in a yield of 64%. 

A soln. of tert-dimy alcohol in DME added to a suspension of Ni(II)-acetate, 2,2 -bi-pyridyl, and NaH in the same solvent at 63° under N2, the mixture stirred for 2 h, a soln. of dibenzothiophene in DME added over 2-3 min, and worked up after 5 h - biphenyl. Y 98%. The reagent efficiently desulfurizes S-heteroaromatics, ar. thioethers, sulfoxides, sulfones and mercaptals (although the efficiency of the last depends on the nature of the substituents on the S atom). F.e.s. S. Becker et al.. Tetrahedron Letters 29, 2963-6 (1988). 

A soln. of thiophenol, ethyl bromide, Na2C03, and a little dichloro[bis(diphenylphos-phino)methane]platinum(II) in acetone boiled overnight ethyl phenyl sulfide. Y 75%. F.e. incl. 1,3-dithioethers, also mercaptals from 1,1-dihalides, s. P.C. Bulman Page et al.. Tetrahedron Letters 29, 4477-80 (1988). 

Bis(alkylthio)pyridines from a-ketoketene mercaptals via p-cyano-a-hydroxyketene mercaptals... 

A mixture of allyltrimethylsilane and bis(phenylthio)methane in toluene added slowly to a soln. of AICI3 in same solvent at room temp., the mixture cooled to 0°, and worked-up when reaction complete by t.l.c. ca. 1-5 h) product. Y 60%. Ketone mercaptals gave a mixture of products. F.e., also thioenolethers using excess of the silane, s. A. Mann et al.. Tetrahedron Letters 29, 6175-6 (1988). 

Di-O -acetyl-1,6 3,6-dianhydro-D-galactohexodialdopyranose, D-500 l,2 3,4-Di-0-isopropylidene-p-D-fl/ ro-hexodialdopyranose, H-83 l,2 3,4-Di-0-isopropylidene-a-D-gfl/flc o-hexodialdo-l,5-pyranose, H-84 g/wco-Hexodialdose D-form Bis(di-Et mercaptal), H-85... 

A method of degradation with excellent preparative possibilities has been devised by MacDonald and Fischer (200), The higher-carbon sugar first is condensed with ethyl mercaptan to form the bis(ethylthio)acetal (mercaptal) (I) (Chapter IV). Oxidation of the mercaptal with perpro-pionic acid then leads to the bis(ethylsulfonyl) compound (II), which is smoothly degraded by aqueous ammonia to the next lower aldose and bis(ethylsulfonyl)methane. 

CaiHggNgS, BenzaIdehyd.bis.[4-benzyUden> amino.naphthyl.(l).mercaptal] 13 1271. 

Cj,Hi4N204S2 Benzaldehyd-bis-[4>nitro-phenyl]-mercaptal 7, 268, II207. 

Hydroxyethylation. Formaldehyde dimethyl mercaptal added during 1 min. to a soln. of KNIL in liq. NH3, then liquefied ethylene oxide added dropwise during 10-15 min. with stirring, after 10 additional min. NH4CI added in small portions -> 3,3-bis(methylthio)-l-propanol. Y 97%. L. Brandsma et al., R. 91, 729 (1972). 

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