Reduction reactions dithianes

Intermediate 10 must now be molded into a form suitable for coupling with the anion derived from dithiane 9. To this end, a che-moselective reduction of the benzyl ester grouping in 10 with excess sodium borohydride in methanol takes place smoothly and provides primary alcohol 14. Treatment of 14 with methanesulfonyl chloride and triethylamine affords a primary mesylate which is subsequently converted into iodide 15 with sodium iodide in acetone. Exposure of 15 to tert-butyldimethylsilyl chloride and triethylamine accomplishes protection of the /Mactam nitrogen and leads to the formation of 8. Starting from L-aspartic acid (12), the overall yield of 8 is approximately 50%, and it is noteworthy that this reaction sequence can be performed on a molar scale. 

The formation of S-oxides has also been observed when oxidizing a variety of 5-substituted 2-tert-butyl-l,3-dithianes in wet acetonitrile. In an undivided cell, 4-substituted 1,2-dithiolane-l-oxides were oblained (Scheme 25) [113]. A coupled cathodic process, in this case, was the reduction of protons formed in the anodic reaction. 

The kinetics of the reduction of 1,2-dithiane with triphenylphosphine was studied in aqueous ethanol at various temperatures by UV spectroscopy <1991PS(60)215>. First-order kinetics was clearly observed and the reaction rate was found to depend strongly on the solvent polarity. 

Oxygen at the heterocyclic sulfur atom has been functionalized in two ways (1) by a TMSOTf-catalyzed Pummerer reaction in the presence of a silyl enol ether (Scheme 95) <1998TL9131> or (2) by reductive removal of the oxygen using Ac20/Zn/cat. 4-dimethylaminopyridine (DMAP) <1996SL885>. The formation of 1,3-dithiane from 1,3-dithiane 1-oxide proceeds efficiently in 95% yield (Equation 70). 

Reduction of N-nitroso compounds 0-97 Reaction between dithiane salts and... 

An efficient synthesis of ( )-quebrachamine is based on the construction of a suitable precursor via ring cleavage of an a-diketone monothioketal (810) (80JCS(P1)457). This monothioketal, available from 4-ethoxycarbonylcyclohexanone ethylene ketal, was fragmented to the dithianyl half ester (811) with sodium hydride in the presence of water. Reaction of (811) with tryptamine and DCC provided an amide which was converted to the stereoisomeric lactams (812) on hydrolysis of the dithiane function. Reduction of either the a- or /3-ethyl isomer with lithium aluminum hydride followed by conversion of the derived amino alcohol to its mesylate produced the amorphous quaternary salt (813). On reduction with sodium in liquid ammonia, the isomeric salts provided ( )-quebrachamine (814 Scheme 190). 

Dithioacetals (see also dithianes and dithiolanes) alkylation of 98 as acyl anion equivalents 75 carbanions of 87,97-102 cleavage of 14-18,98,102 desulfurization of 78 metal-catalysed coupling 127 reaction with Grignard reagents 127 reductive lithiation of 89 synthesis of 12-19,97-102 Dithioacids synthesis of 40... 

A 1,2-carbonyl transposition sequence based on the Woodward dithioacetalisa-tion reaction was used to relocate a carbonyl group in 95.1 [Scheme 2.95] to the adjacent position in 95 6.190 A total of 6 steps were required in which the key step was the dithioacetalisation of the a-hydroxymethylene derivative 95 2. After reduction of the carbonyl group, the dithiane was hydrolysed to the a-acetoxy ketone whence dissolving metal reduction removed the acetate function. 

Shono and coworkers [203] reported a synthetically useful reductive cyclization reaction of y-hydroxyphenylsulfides leading to the formation of stereoisomeric cyclopropanes, but the iosmer ratio was not determined. Ethylene bis-dithiobenzoate is also reductively cyclized in dry acetonitrile containing methyl idodie to give nonstereoselectively d, /-and /ne o-dithiane derivatives in good yield [204]. 

Reaction of lithiodithianes with acyl chlorides, esters or nitriles leads to the fOTination 1,2-dicarbonyl compounds in which one of the carbonyl groups is protected as the thioacetal. d76043j44 Optically active amino ketones of type (69) are inepared via acylation of dithiane with an oxazoline-protected (5)-serine methyl ester (Scheme 41). Optically active (5)-2-alkoxy-l-(l,3-dithian-2-yl)-l-propanones were prepaid by the reaction of the corresponding methyl (5)-lactate with 2-lithio-l,3-enantioselective synthesis of (-)-trachelanthic acid. Enantioselective synthesis of L-glyceraldehyde involves the acylation of a dithiane glycolic acid derivative followed by bikers yeast mediated reduction. ... 

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