Dithianes hydroxy

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]. 

Ethyl (2/ , 3.S )-4-(T,3-Dithian-2-ylidene)-2-hydroxy-2,3-dimethylbutanoate Typical Procedure37 ... 

Acctoxy-1- 3-(1,3-dithian-2-ylidenc)propj ll-5-hydroxy-2-pyrroIidinone (2) Typical Procedure35 ... 

A solution of 6.13 g (15.9nunol) of (3S.4R)-3,4-[cyclohexylidenebis(oxy)]-1-[4-(l,3-dithian-2-yli-dene)butyl]-5-hydroxy-2-pyrrolidinone and 4.4 mL (31.8 mmol) of triethylaminc (freshly distilled from CaH,) in 15 mL of Ch,C12, in a 100-mL flame-dried round-bottomed flask, is cooled to 0"C and then... 

Bohman and Allenmark resolved a series of sulphoxide derivatives of unsaturated malonic acids of the general structure 228. The classical method of resolution via formation of diastereoisomeric salts with cinchonine and quinine has also been used by Kapovits and coworkers " to resolve sulphoxides 229, 230, 231 and 232 which are precursors of chiral sulphuranes. Miko/ajczyk and his coworkers achieved optical resolution of sulphoxide 233 by utilizing the phosphonic acid moiety for salt formation with quinine. The racemic sulphinylacetic acid 234, which has a second centre of chirality on the a-carbon atom, was resolved into pure diastereoisomers by Holmberg. Racemic 2-hydroxy- and 4-hydroxyphenyl alkyl sulphoxides were separated via the diastereoisomeric 2- or 4-(tetra-0-acetyl-D-glucopyranosyloxy)phenyl alkyl sulphoxides 235. The optically active sulphoxides were recovered from the isolated diastereoisomers 235 by deacetylation with base and cleavage of the acetal. Racemic 1,3-dithian-l-oxide 236... 

The value of 2-acyl-1,3-dithiane 1-oxides in stereocontrolled syntheses has been extended to the enantioselective formation of (3-hydroxy-y-ketoesters through ester enolate aldol reactions <00JOC6027>. 

Ring enlargement.1 A new route to seven-membered ring systems from a cyclohexenone (1) involves a photocycloaddition of ethylene to provide the bicy-clooctanone 2. Addition of lithio-1,3-dithiane to 2 provides the adduct 3, which on reaction with HgO and HBF4 forms an unstable rearranged hydroxy aldehyde... 

The procedure for the preparation of a dithiolane from a hydroxy-methylene derivative of a ketone and ethylene dithiotosylate (ethane-1,2-dithiol di-p-toluenesulfonate) can be varied to produce dithianes when the latter reagent is replaced by trimethylene dithiotosylate.8,4 The dithiotosylates also react with enamine derivatives to produce dithiaspiro compounds.4,5... 

The lithiation of y-chloro acetal 175 with lithium and a catalytic amount of naphthalene (4%) allowed the preparation of the intermediate 176, which can be considered as a masked lithium homoenolate, and was used for the preparation of the hydroxy ketone 179 through the hydroxy acetal 177 and dithiane 178 using known chemistry (Scheme 62)" . 

The phosphine-mediated desulfurization of substituted 1,2-dithianes to the corresponding tetrahydrothiophenes proceeds stereospecifically for the corresponding reactions of cis- and /ra r, 5-dihydroxy-l,2-dithianes 124 and 125/126, three different phosphines R3P (R=Et, Ph, (CH2)2COOH-HCl) were employed <2003H(60)47>. The reaction is pH-dependent under mildly acidic conditions, the thiols 127 and 128 were obtained under neutral or moderately basic conditions, however, the 4-hydroxy-3-mercaptotetrahydrothiophenes 129-131 were formed (Scheme 32). Erom 124 and 125 racemic 129 and 130 were obtained, while for 126 the stereospecific product 131 was isolated the identity of... 

The photolysis of /ra r-4,5-dihydroxy-l,2-dithiane in aqueous and CH2CI2 solutions yielded the two isomers (the /ra r-orientation of the hydroxy substituents remains constant) of 3,4-dihydroxy-2-mercaptotetrahydrothiophene which were characterized by H and NMR and electrospray ionization (ESI) MS <2004PCA2247>. 

An intramolecular cycloaddition occurred, when 2-alkylidene-l,3-dithianes having a hydroxy group at an appropriate distant position (3- or 4-atoms) were treated with trifluoromethyl iodide in the presence of SO2. A radical mechanism with 2-alkyl-2-iodo-l,3-dithianes as intermediates is suggested (Equation 37) <1997JOC9107>. 

Radical cations of 2-alkylidene-l,3-dithianes can be generated electrochemically by anodic oxidation using a reticulated vitreous carbon (RVC) anode <2002TL7159>. These intermediates readily react with nucleophiles at C-1. Upon removal of the second electron, the sulfur-stabilized cations were trapped by nucleophilic solvents, such as MeOH, to furnish the final cycloaddition products. Hydroxy groups <20010L1729> and secondary amides <2005OL3553> were employed as O-nucleophiles and enol ethers as C-nucleophiles (Scheme 50) <2002JA10101>. 

An unexpected reactivity in the functionalization of 2-acyl-l,3-dithianes has been reported by Mioskowski and co-workers. They found that 2-acyl-l,3-dithianes with no further heteroatom at the acyl side chain react with aldehydes to give 2-acyl-2-hydroxyalkyl-l,3-dithianes, whereas a silyl-protected hydroxy group in the side chain of the 2-acyl-l,3-dithiane led to formation of the aldol product at the opposite site of the carbonyl group. Acyl chlorides always react with 2-acyl-l,3-dithianes to give the enol esters (Scheme 81) <2003TL213>. 

CEJ1358> and the ruthenium mediated isomerization of double bonds (cf. Scheme 89, Section 8.11.7) <2007TL137> are recent examples of transition metal catalyzed manipulations at the side chain carbon atoms of 1,3-heterocycles. A novel side-chain addition reaction of aldehydes to 6-alkylidene-l,3-dioxin-4-ones was used for the construction of intermediates of lophotoxin <2006CJC1226>. An acid-catalyzed intramolecular cycloaddition of a hydroxy group to an alkene has been effected by the presence of an adjacent 1,3-dithiane moiety <2006TL4549>. 

A considerable number of electrophiles were used, and the dithiane route found great utility for the syntheses of simple monofunctional compounds as well as for polyfunctional molecules, for which the dithiane moiety affords an invaluable temporary protection of a future carbonyl group. Some experimental procedures published in Organic Syntheses — cyclobutanone [277] and 3-hydroxy-l-cyclohexene-l-carboxaldehyde [278] — are illustrative. A similar route to aldehydes [279] makes use of sym-trithiane as a formyl anion equivalent. 

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