Acetals diethers

These reactions ate carried out in the presence of acidic and basic catalysts. The acid-cataly2ed addition of ethyl alcohol to acetylene or to a vinyl ether produces acetals (diethers of 1,1-dihydroxyethane). The acid-cataly2ed reaction of ethyl alcohol with an aldehyde or ketone also gives acetals. 

Many of the most interesting and useful reactions of aldehydes and ketones involve trans formation of the initial product of nucleophilic addition to some other substance under the reaction conditions An example is the reaction of aldehydes with alcohols under con ditions of acid catalysis The expected product of nucleophilic addition of the alcohol to the carbonyl group is called a hemiacetal The product actually isolated however cor responds to reaction of one mole of the aldehyde with two moles of alcohol to give gem mal diethers known as acetals... 

Catechols can be protected as diethers or diesters by methods that have been described to protect phenols. However, formation of cyclic acetals and ketals (e.g., methylenedioxy, acetonide, cyclohexylidenedioxy, diphenylmethylenedioxy derivatives) or cyclic esters (e.g., borates or carbonates) selectively protects the two adjacent hydroxyl groups in the presence of isolated phenol groups. 

The reaction of butyllithium with 1-naphthaldehyde cyclohexylimine in the presence of (/C )-l,2-diphenylethane-1,2-diol dimethyl ether in toluene at —78 °C, followed by treatment with acetate buffer, gave 2-butyl-1,2-dihydronaphthalene-l-carbaldehyde, which was then reduced with sodium borohydride in methanol to afford (1 R,2.S)-2-butyl-1 -hydroxymcthyl-1,2-dihydronaphthalene in 80% overall yield with 91 % ee83. Similarly, the enantioselective conjugate addition of organolithium reagents to several a,/J-unsaturated aldimines took place in the presence of C2-symmetric chiral diethers, such as (/, / )-1,2-butanediol dimethyl ether and (/, / )- ,2-diphenylethane-1,2-diol dimethyl ether. 

An organic sulfur compound containing an acetal function had been oxidised to the sulfone with 30% hydrogen peroxide in acetic acid. After the liquor had been concentrated by vacuum distillation at 50-60°C, the residue exploded during handling. This was attributed to formation of the peroxide of the acetal (formally a gem-diether) or of the aldehyde formed by hydrolysis, but formation and explosion of peracetic acid seems a more likely explanation. 

The base lability of succinoyl diester hnker severely limits the selection of protecting groups available for an oligosaccharide synthesis, so a more versatile tether was required. Diether bonds of benzylphenol or dibenzyl of 1,4-di(hydroxymethyl)-benzene satisfy this requirement because they are stable to both bases and to acids. A sufficient acid stability is important since the formation of a glycosidic bond is an acid-catalyzed reaction, not surprisingly, as it is an acetal functionality. For instance, DOX,34 the dibenzyl hnker a,a -DiOxyXylyl diether, -0CH2C6H4CH20-, is not limited by restriction of the succinoyl hnker (1) when bound via a hydroxyl or as an... 

Similarly, thermolysis of naphthacene photooxide (329) leads to naphtha-cenequinone (330), the bicyclic acetal 331, and the cyclobutene diether 332.178 These products are shown to have been formed by the involvement of the meso-diepoxide 333 by means of trapping experiments. 

Martmez-Bernhardt, R. Castro, P. P. God-joian, G. Gutierrez, C. G. Substituted diether diols by ring-opening of carbocyclic and stan-nylene acetals. Tetrahedron 1998, 54, 8919-8932. 

Certain diethers of the type ROCHaCH OR have been prepared by adding alkyl halides to a solution of sodium in excess ethylene glycol monoalkyl ether, as in the preparation of ethylene glycol dimethyl ether (78%). Chloromethyl methyl ether and alcohols react to give an acetal derivative of formaldehyde, CHjOCHjOR the reaction is carried out in the presence of pyridine. Aromatic diethers such as 2-methoxydiphenyl ether have been prepared by the Ullmann procedure. ... 

Hydroboration is faster than cleavage with borane, but H2BCI etherate cleaves unsaturated acetals without giving hydroboration (equation 10). Lower yields are obtained with the less reactive Me2S complex, but that reagent gives good yields of dihydroxy diethers from chiral bisacetals (equation 11). The diethyl acetal of benzaldehyde can be reduced to ethyl benzyl ether in moderate yield by decaborane in toluene at 120-130 C (equation 12). °... 

Heating the keto ester (26.7) with sodium hydride and a catalytic amount of t-butyl alcohol converts it into the isocoumarin in good yield. A 2-acyl(or formyl)indole-3-acetic acid is cyclized by heating in acetic anhydride or on stirring with the anhydride for 36 h [3741,3937]. The latter process is sometimes shortened by addition of boron trifluoride dietherate [3742]. 

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