Acetal Cleavage Reactions

Reductive cleavage with lithium aluminium hydride-aluminium chloride, or with sodium cycloborohydride-hydrochloric acid, or with aluminium chloride-trimethylamine, of endo-3t4-0-(4-methoxybenzylidene) acetal rings of 1,6-anhydro- -D-galactopyranose derivatives gives predominantly the axial 3-0-(4-0-methoxybenzyl)ether derivatives. Oxidative cleavage with DDQ affords the axial 3-0-(4-inethoxybenzoyl) 

As mentioned above aqueous tetrafluoroboric acid rapidly and cleanly cleaves acetals in acetonitrile solution. 

Koos and H.S.Mosher, Collect. Czech. Chem. Commun., 1985, 1994. 

Kloosterman, J.H.Van Boom, P.Chatelard, P.Boulanger, and G.Descotes, Tetrahedron Lett., 1985, 2A, 5045. 

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Introduction. (l/ ,5i -2//-l,5-Benzodithiepin-3(4/ -one 1,5-dioxide (C2-symmetric his-sulfoxide 1) has been used as a chiral auxiliary for asymmetric desymmetrization of cyclic meso-1,2-diols via diastereoselective acetal cleavage reaction. The procedure consists of three steps (eq 1), that is, acetalization (step 1), acetal cleavage reaction followed by benzylation (step 2), and hydrolysis of the vinyl ether (step 3). Due to the Ca-symmetry of 1, the chiral auxiliary gives only one product in step 1. In addition, no regio- or geometric isomers of the enol ether are formed in step 2. This reagent can be recovered by acid-promoted hydrolysis and reused. 

The reaction is based, on the one hand, on the oxidative cleavage of vicinal diols by lead(IV) acetate and, on the other hand, on the reaction of dichlorofluorescein with lead(IV) acetate to yield a nonfluorescent oxidation product. The dichlorofluorescein only maintains its fluorescence in the chromatogram zones where the lead(IV) acetate has been consumed by the glycol cleavage reaction [1],... 

In this type of cleavage reaction, it appears that the axial benzoate is the preferred product. If water is excluded from the reaction, a bromo benzoate is obtained.The highly oxidizing medium of 2,2 -bipyridinium chlorochromate and MCPBA in CH2CI2 at rt for 36 h effects a similar conversion of benzylidene acetals to hydroxy benzoates in 25-72% yield. ... 

Ethyl dimethylacetoacetate reacts instantly at room temperature when treated with ethoxide ion to y- ield two products, ethyl acetate and ethyl 2-methylpropanoate. Propose a mechanism for this cleavage reaction. 

The involvement of carbenes has been excluded in the DNA cleavage reactions activated by cupric acetate as these experiments were conducted in the dark. However, the contribution of metal-carbenoids [79] could not be ruled out. In a series of studies dealing with the metal-catalyzed... 

Schnur and co-workers " summarized typical reactions that can be performed on functional groups of substituted 2,4-oxazolidinediones without ring opening. These reactions include reduction with iron-acetic acid, chlorosulfonation, nucleophilic displacements of aromatic fluorides, and acid hydrolysis with HCl/formic acid. Nonetheless, there are examples of useful ring cleavage reactions involving 2,4-oxazolidinediones. 

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