Acetal cyclic

In 1970, it was disclosed that it is possible to achieve the conversion of dimethylformamide cyclic acetals, prepared in one step from vicinal diols, into alkenes through thermolysis in the presence of acetic anhydride." In the context of 31, this two-step process performs admirably and furnishes the desired trans alkene 33 in an overall yield of 40 % from 29. In the event, when diol 31 is heated in the presence of V, V-dimethylforrnamide dimethyl acetal, cyclic dimethylformamide acetal 32 forms. When this substance is heated further in the presence of acetic anhydride, an elimination reaction takes place to give trans olefin 33. Although the mechanism for the elimination step was not established, it was demonstrated in the original report that acetic acid, yV, V-dimethylacetamide, and carbon dioxide are produced in addition to the alkene product."... 

Reaction of diols with acetals (cyclic acetals)... 

The reaction of five-membered cyclic N,N-acetals results in ring expansion with CO incorporation to give cyclic enediamines with no silyl moiety. No reaction is observed for alkyl-substituted cyclic N,N-acetals. Cyclic N,0-... 

Cyclic Acetals Formation of an acetal using a diol as the alcohol gives a cyclic acetal. Cyclic acetals often have more favorable equilibrium constants, since there is a smaller entropy loss when two molecules (a ketone and a diol) condense than when three molecules (a ketone and two molecules of an alcohol) condense. Ethylene glycol is often used to make cyclic acetals its acetals are called ethylene acetals (or ethylene ketals). 

Orthoesters are usually cleaved by acid hydrolysis using conditions similar to those normally employed for acetals however, OBO groups can be hydrolysed in the presence of acetals.225 As with acetals, cyclic orthoesters are more stable than their acyclic counterparts. The product of mild acid hydrolysis is itself an ester which must then be further treated with base (pH 10-11) to... 

CYCLIC CARBONATES Performic acid. CYCLIC DISULFIDES Lead acetate. CYCLIC KETONES p-Toluenesulfonyl-hydrazine. 

For the cyclic AMP assay [y- P]ATP (10 uM) is incubated with 10 mM magnesium acetate, cyclic AMP standard (0-10 pmol) or water, histone mixture, cyclic AMP-activated protein kinase, and 0.1 M sodium acetate buffer, pH 6.0, for 5 min at 30°C. The reaction is terminated by the addition of trichloroacetic-acid-tungstate-sulfuric acid, the precipitate is dissolved in N NaOH, and the radioactivity counted in scintillation fluid. 

The exchange of alkoxy groups for the cyanide function can also be achieved in acetals (cyclic types like dioxolanes and 1,3-dioxane derivatives included), 5A -acetals and ortho esters with the combination of TMS-CN/Lewis acids, or under neutral conditions with transition metal salts as catalysts (Scheme 16). Furanose derivatives may be treated with TMS-CN in a similar way. ... 

In addition to toe ketals and the acetals, cyclic orthoesters are sometimes used for the protection of 1,2-diols. They are more readily cleaved by acids than the acetonides. In nucleoside chemistry formic acid, acetic acid and benzoic acid orthoesters were applied to temporarily mask the carbohydrate part. ° Also the metooxyacetic acid orthoester (55) was useful because it allowed the selective liberation of toe 3 -... 

Cyclic carbonates have been reviewed, and so will not be included here. Acyclic acetals, cyclic phosphates, sulfites, boronates, and orthoesters, together with the acetals from trichloroacetaldehyde, are omitted. 

Ring- Cyclic ethers Cyclic acetals Cyclic sulfides Cyclic amines... 

Synthesis of cyclic acetals Cyclic ketals (potential cosmetics ingredients) have been obtained in excellent yields from a cineole ketone under the action of microwave in solvent-free conditions or in toluene. The results reported compared very favorably with those obtained by use of conventional heating (Eq. (39), Table 4.11) [123]. 

Premphase Conjugated estrogens Medroxyprogesterone acetate (cyclic)... 

The only functional group in either compound is an acetal. Cyclic acetals are made from diols and carbonyl compounds so we need to have a look at the deprotected molecules before taking any further decisions. 

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