1.4- dithiane-2,5-diol

It has been shown that Lewis acid catalyzed isomerization of thionolactones provides access to thiolactones. For example, exposure of the substrate 22 to catalytic amounts of BF3 OEt2 led to efficient conversion to the thiolactone 23. Such transformations were also found to give minor amounts of lactone or dithiolactone side products <06TL6067>. Substituted tetrahydrothiophene derivatives have also been obtained from 1,4-dithiane-2,5-diol and 2-nitroethyl acetate derivatives by a base induced sequence featuring a Michael addition and a Henry reaction <06TL8087>. 

Similarly, in another example, alkylation of 111 with diepoxide (—)-115 (1 equiv.) in the presence of HMPA (1.3 equiv.) furnished diol (+)-117. Protection of (+)-117 to form the acetonide, removal of the silyl protecting groups (TBAF), and hydrolysis of the dithiane with Hg(Cl04)2 provided the diketone (+)-118. Hydroxy-directed syn-reduction of both carbonyl groups with NaBI U in the presence of Et2BOMe, and triacetonide formation, followed by hydrogenolysis and monosilylation, afforded the desired Schreiber subtarget (+)-119, which was employed in the synthesis of (+)-mycoticins A and B (Scheme 8.31) [56b]. 

Enantiopure 77 was easily prepared by treatment of 2-trimethylsilyl-l,3-dithiane 75 and chiral epoxides 76 in a sequential addition in the presence of a crown ether. In this sequence, a monosUylated 1,5-diol 77 is obtained, allowing a discrimination of the two... 

The efficient resolution of /ra r-4,5-dihydroxy-l,2-dithiane into the two enantiomers in large quantities has been reported by the reaction of the racemic mixture with the amino acid iV-/-butoxycarbonyl-(5)-phenylalanine <1997TL7657>. By fractional crystallization, the (43, 53 )- and (4/J,5iJ)-esters were separated followed by hydrolysis, which provided the desired enantiomeric diols in excellent yield and >99% ee. These reactive diols provide isomerically pure analogs with interesting selectivity and therapeutic potential for example, 4,5-dihydroxy-l,2-dithiane derivatives have been reported to inhibit the replication of HIV-1 and HIV-2 (human immunodeficiency viruses). 

The method ZC3Z + C is used for the preparation of reduced pyrimidines, oxazines and thiazines as well as for dioxanes, dithianes and oxathianes as mentioned above (e.g. 258 — 257, 259 Z, Z = NH, O, S). The Prins reaction yields 1,3-dioxanes (77S661) it involves the acid-catalyzed condensation of alkenes with aldehydes with 1,3-diols as intermediates. 

Dithiins are prepared by vapor phase dealkoxylation of 2,5-dialkoxy-l,4-dithianes (from HSCH2CH(OEt)2 + H+) over alumina at 260-265°C (306 — 307). 2,5-Diaryl derivatives can be prepared from Bunte salts (308 Scheme 46) with acid via the intermediate diol (309). 

Nucleophilic attack of lithiated dithiane 8 on the lithium alkox-ide of 24 gives 1,3-diol 9. 

Reaction of 2equiv of acrolein with 1 equiv of l,4-dithiane-2,5-diol 473 gives dihydrothiophene-3-carboxaldehyde 474 (Scheme 79) <2001SC1527>. 

The high diastereoselectivity attending the spirocyclisation of ketene dithioacetals provides an effective means for controlling the stereochemistry of a methyl substituent at the a-position on a 6-lactone ring,244 The method was applied to the synthesis of the polyether antibiotic Salinomycin [Scheme 2.120].242 Condensation of the methyl ketone 120 1 with the lithiated l,3-dithian-2-yl-phospho-nic acid diethyl ester 120.2 gave the ketene dithioacetal 1203 in 76% yield. After hydrolysis of the two benzoate ester groups, cyclisation of diol 120.4 was... 

Each diol was converted into the corresponding a- and P-epoxides, which were opened regioselectively by 2-lithio-l, 3-dithiane. The complete sequence from anti-S is formulated in equation (I)/... 

Zincio-I,3-dithianes are valuable reagents. Based on reactions of organozincs 4-acetoxy-l,3-dioxanes serve as precursors of anti-l,3-diols." A synthesis of 1,1-diarylallenes involves Pd-catalyzed coupling of the organozinc species which are derived from 1-arylpropynes by lithiation and Li/Zn exchange with aryl halides. By an sp -sp bond formation process to introduce a dienyl substituent to C-2 of 2-cyclopentenones a facile synthesis of nakienone-A was developed. - ... 

DIHYDRO-3-FURANONES 2,2-Dimeth-oxymethyl-1,3-dithiane. DIHYDRO-y-PYRONES 2,2-Dimethoxy-methyl-1,3-dithiane. vic-DIOLS Titanium(III) chloride. o-DIKETONES Potassium permanganate-Acetic anhydride. Ruthenium tetroxide. 

The successive reaction of (dibromomethyl)silanes with LDA (hthium diisopropyl-amide) and two equivalents of benzaldehyde gives 1,3-diol monosilyl ethers in good yield (Scheme 10.221) [574]. This tandem reaction would proceed via anionic 1,3-silyl migration of /l-lithioxyalkylsilane intermediate 152 and addition of the resulting lithium carbenoid to benzaldehyde. Thus, internal activation of the silicon-lithium alkoxide promotes nucleophilic addition of a-haloalkylsilanes. Similar tandem reactions of 2-trimethylsilyl-l,3-dithiane with aldehydes [575] and epoxides [576] have been reported. 

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