Dithioacetals from ketones

Less is known concerning the partial, acid hydrolysis of alditol polyacetals derived from ketones, compared to those derived from aldehydes. The acid hydrolysis of 1,2 3,4 5,6-tri-O-isopropylidene-D-mannitol to 3,4-O-isopropylidene-D-mannitol55,56 and of l,2 3,4-di-0-isopropylidene-L-rhamnitol to 3,4-O-isopropylidene-L-rhamnitol57 indicates an order of isopropylidene acetal stability of a-threo > a, and this order is supported by the partial hydrolysis of 2,3 4,5-di-O-isopro-pylidene derivatives of dialkyl dithioacetals of D-arabinose58 and D-xylose59 to 2,3-acetals. 

Dithianes are extremely important compounds in organic synthesis because going from ketone to thioacetal inverts the polarity at the functionalized carbon atom. Aldehydes, as you are well aware, are electrophiles at the C=0 carbon atom, but dithioacetals, through deprotonation to an anion, are nucleophilic at this same atom. 

Looking carefully at the current literature we have learned that the ketene dithioacetal chemistry, widely used for one-carbon homologation of carbonyl compounds, has never been utilized for the construction of ulosonic acids [129]. Besides, ketene dithioacetals, readily available from ketones and aldehydes via the reaction with the ylides generated from substituted dithioacetals in the Peterson, Wittig or Homer-Emmons olefmation, have never been synthesized from lactones. 

Entries 3 to 5 show the use of alternative sources of the one carbon unit. In Entry 3, a tertiary alcohol is formed with one of the alkyl groups being derived from the dithioacetal reagent. Related procedures have been developed for ketones and tertiary alcohols using 2-lithio-2-alkyl-l,3-benzothiole as the source of the linking carbon.14 Problem 9.3 deals with the mechanisms of these reactions. 

The a-oxoketene dithioacetals 6 (6.1-6.43) employed in this work as three carbon 1,3-biselectrophilic components have been drawn from various active methylene ketones and are described in the Table-1. The corresponding a-oxoketene N,S- and 0,S-acetals (17.1- 17.15) which are usually derived from a-oxoketene dithioacetals are described in Table-2. These examples are only a representative groups to demonstrate the general application of the new Jl-heteroaromatic annulation methodology... 

Synthesis of Benzoheterocycles from Heterocyclic Ketone Derived a-Oxoketene Dithioacetal Precursors... 

The above examples represent Jl-heteroaromatic annulation involving the reaction of allyl anions whose double bond is a part of the heterocyclic ring system (Scheme 1). The corresponding a-oxoketene dithioacetals (1,3-electrophilic component) were generally derived from nonheterocyclic carbonyl precursors. Alternatively the Jl-heteroaromatic annulation can also be employed to a-oxoketene dithioacetals derived from heterocyclic ketones (1,3-bielectrophile) and hetero/nonheteroallyl anions (1,3-binucleophile). These reactions are described below. 

Ethylene and 1,2-diphenylethylene dithioacetals derived from different ketones decompose upon irradiation (high-pressure mercury lamp) in the presence of oxygen to the parent ketones (see Scheme 21) the reported - yields were 57-90%. In an analogous case that may serve as... 

The stoichiometric equivalents of halofluorides have been recently applied to transform alkylene dithioacetals into gcm-difluorides.70-71 Dithioacetals such as 1,3-dithiolanes and 1,3-dithianes arc readily obtained from the corresponding carbonyl compounds by the reaction with ethane-1,2-dithiol or propane-1,3-dithiol in the presence of the complexes boron trifluoride-bis(acetic acid) or boron trifluoride-diethyl ether. Using a two-step procedure, a range of aldehydes and ketones can be converted into gem-difluorides under mild conditions. 

The syntheses of dithioacetals are generally straightforward [43]. Standard methods may be unselective for multifunctional molecules. Therefore, new procedures have been developed. It has thus been reported that 1,3-dithianes are readily synthesized by reaction of aldehydes, ketones or acetals with 2-stanna-l,3-dithianes under catalysis of organotin triflates [45]. These odourless reagents are prepared from dialkyldichlorotin and 1,3-propanedithiol. 

Alcohols can be selectively oxidized in the precence of dithioacetals derived from unconjugated ketones.83,101 On the other hand, the thioacetals at benzylic and allylic positions can be hydrolyzed under very mild conditions with IBX in DMSO in the presence of traces of water.102... 

In a recent approach to the preparation of dihydro-3(2H)-furanones by chemists from Thailand it was shown that consecutive, one-pot conventional treatment of 1,3-dithiane in THF with equimolar n-butyllithium, an epoxide, n-butyllithium, an aldehyde or ketone and, finally, methanesulfonyl chloride gave a spirocyclic dithioacetal in good (ca. 70%) yield. Hydrolysis with HgO/HgCl2 gave the corresponding dihydrofuranone. 

Salicylaldehyde reacts with trimethylsilylketene dithioacetal in the presence of a Lewis acid to form the chroman 502, the product of a deoxygenative divinylation (Equation 208) <2001JOC3924>. This reaction can also be applied to salicylaldimines <2003JOC4947>. Treatment of 3,5-dibromosalicylaldehyde with methyl vinyl ketone (MVK) in the presence of DABCO leads to a chroman-4-ol as the major product <2002J(P1)1318>. A stereoselective one-pot synthesis of vy/z-fused chromans from salicylaldehydes, aromatic amines and cyclic enol ethers is carried out in the... 

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