Cyclic diol diacetates

Table 11.1-3. Pig liver esterase-catalyzed enantiotopos-differentiating hydrolysis of prochiral cyclic diol diacetates in aqueous solution.

Table 11.1-7. a-Chymostrypsin-catalyzed enantiotopos-differentiating hydrolysis of prochiral cyclic dicarboxylic acid esters, acyclic dicarboxylic acid esters and cyclic diol diacetates and enantiomer-differentiating hydrolysis of racemic carboxylic acid esters in aqueous solution. 

Meso Compounds. Although pig liver esterase is by far the most suitable enzyme for asymmetric transformations involving meso compounds, especially diacids, there are several reports on the lipase-catalyzed hydrolysis and transesterification reactions of cyclic diol derivatives. The former includes variously substituted cycloalkene diacetates, cyclohexylidene protected erythri-tol diacetate, piperidine derivatives, and the exo-acetonide in eq 11. Complementary results are clearly demonstrated in eq 11 and eq 12 for the hydrolysis and esterification processes. 

Evidence that the reaction of the diol ester 5 with antimony pen-tachloride genuinely involves a neighboring-group reaction is provided by the stereospecificity of this reaction with esters of cyclic diols. trans -l,2-Cyclopentanediol diacetate (14) and Irons-1,2-cyclo-hexanediol diacetate (17) react " with antimony pentachloride to give the cis-acetoxonium salts 15 and 18, whereas the cis-diol esters (16 and 19) merely give difficultly soluble adducts from which unchanged starting material can be recovered after hydrolytic treatment. 

Although several more examples of this type of ring system are known in the literature, the majority of these are cyclic diacetals, which have been used for the protection of diols. These have not been included in this chapter the reader is directed to the chapters dealing with the relevant diols. 

Acetals are readily formed with alcohols and cyclic acetals with 1,2 and 1,3-diols (19). Furfural reacts with poly(vinyl alcohol) under acid catalysis to effect acetalization of the hydroxyl groups (20,21). Reaction with acetic anhydride under appropriate conditions gives the acylal, furfurylidene diacetate [613-75-2] (22,23). 

Vicinal dioxalates are cleaved electrochemically to alkenes in DMF at a less negative potential ( —1.2 V vs. Ag/AgI) than vicinal diacetates or diols [72,73]. Oxalic esters of monohydric alcohols give quasi-reversible peaks in cyclic voltammetry, whereas oxalates of vicinal diols give irreversible peaks. Oxalates of the diols may be formed through a rapid, base-catalyzed transesterification using diethyl oxalate, for example [74]. 

Aromatic polyesters were enzymatically synthesized under mild reaction conditions. Divinyl esters of isophthalic acid, terephthalic acid, and p-phen-ylene diacetic acid were polymerized with glycols by lipase CA catalyst to give polyesters containing an aromatic moiety in the main chain.208 In the lipase-catalyzed polymerization of dimethyl isophthalate and 1,6-hexanediol in toluene with nitrogen bubbling, a mixture of linear and cyclic polymers was formed.209 High molecular weight aromatic polyester (Mw 5.5 x 104) was synthesized by the lipase CA-catalyzed polymerization of isophthalic acid and 1,6-hexanediol under vacuum.210 Enzymatic polymerization of divinyl esters and aromatic diols also afforded the aromatic polyesters.211... 

Cyclic dimethanol derivatives have been extensively studied not only in lipase-catalyzed hydrolysis (Table 11.1-11) but also in lipase-catalyzed enantioselective acylation for synthetic and mechanistic reasons (1-16, 20, 30, 32, 33, 37, 40, 45, 47-53, 57-62, 66, 72) (Table 11.1-18). Generally, enantioselectivities in acylation of the diol and hydrolysis of the corresponding diacetate yielding enantiomeric com-... 

In the case of peraksine [RP-5 (27)] it was shown to have the formula C19H22N2O2, a fact not readily derived from combustion analysis since the free base crystallized from alcohol in a hydrated form (27). It has also been observed that this water of solvation could be displaced by chloroform (20). Peraksine has UV-absorption typical of a 2,3-disub-stituted indole and reacted with benzoyl chloride to form an 0-benzoyl derivative. The second oxygen was apparently present as a cyclic ether when it was found that although peraksine did not react with hydrazine derivatives, it was reducible with sodium borohydride to furnish a diol (mp 290°-291° [a]j) - -41° in Py diacetate, mp 103°-105°). This diol readily lost the elements of water upon acid treatment to afford a new ether, deoxyperaksine, 230° change in crystalline form (mp 255°-257°). Because of these properties peraksine was considered to possess a cyclic hemiacetal moiety. 

Cyclic diacetals of glutaraldehyde are prepared in fair yields by KlO-promoted reaction of 2-ethoxy-2,3-dihydro-4//-pyran with diols, under benzene azeotropic dehydration (eq 2). ... 

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