Diols cycloalkenes

The 1,4-diacetoxylation was also extended to the use of other acyl groups than acetyl. Thus, an unsymmetrical 1,4-acetoxy-trifluoroacetoxylation of 1,3-dienes was developed by the use of added trifluoroacetic acid to the acetic acid used as the solvent330. With the use of acetone as the solvent with an added carboxylic acid a general diacyloxylation was obtained and, for example, the 1,4-dibenzoates of 2-cycloalkene-l,4-diols were prepared directly from the corresponding l,3-cycloalkadienes33d. 

Alkenes may also react with certain oxidizing agents to result in anti hydroxyla-tion. Treatment with peroxycarboxylic acids435 leads initially to an epoxide. Ring scission of the latter via an SN2 reaction in an anti manner with the corresponding carboxylic acid or water gives the trans monoester or tram diol, respectively. Complete anti stereoselectivity and high yields in the oxidation of cycloalkenes are... 

Oxidation with lead tetraacetate is a far less selective process.490,491 Studied mainly in the oxidation of cycloalkenes, it gives stereoisomeric 1,2-diol diacetates, but side reactions (allylic acetoxylation, skeletal rearrangement) often occur. A change in reaction conditions in the oxidation of cyclopentadiene allows the synthesis of different isomeric mono- and diesters.492... 

Each of these reagents produces cis- 1,2-dihydroxy compounds (diols) with cycloalkenes ... 

Olah et al.724 have shown that Nafion-H induces the ring opening of oxiranes under mild conditions to afford various products. Substituted oxiranes undergo hydrolysis or alcoholysis to yield 1,2-diols or 1,2-diol monoethers, when treated with Nafion-H under mild conditions in the presence of water or alcohols, respectively. Cycloalkene oxides give the corresponding trans products stereoselectively [Eq. (5.273)]. 

Thallium(in) sulfate in water brings about the anti hydroxylation of 3-r-butyl- and 4-r-butyl-cyck>-hexene. The reagent has been recommended for the one-step preparation of rranj-diols from ctmfor-mationally rigid cycloalkenes. 

Acid-catalyzed epoxide cleavage takes place by back-aide attack nucleophile on the protonated toxide in a manner analogous to the step of alkene bromtnation, in ndiich a cyclic brentORtunt ion is opened nucleophilic attack (Section 7.2l. When an opoxycycloalkane is opened aqueous acid, a frona-t -diol results just as a traR5 l,2-dibroiiiide from cycloalkene hrominaUun. 

Lipase-catalyzed asymmetric hydrolysis has also been conducted on numerous monocyclic, variously substituted five-, six-, and seven-membered cycloalkane and cycloalkene secondary alcohols and diols. More recent reports include cis-4-acetoxyflavan, substituted cyclopentenones, and the 1,2-bis(hydroxymethyl)cyclobutanol derivative exemplified in eq 3. ... 

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. 

The asymmetric transesterification of cyclic me o-diols, usually with vinyl acetate as an irreversible acyl transfer agent, includes monocyclic cycloalkene diol derivatives, bicyclic diols, such as the ej o-acetonide in eq 12, bicyclic diols of the norbomyl type, andorganometallic l,2-bis(hydroxymethyl)ferrocenepossessing planar chirality. 

Hydroxylation, the addition of two hydroxyl groups across double bonds, converts alkenes and cycloalkenes into vicinal dials. Stereochem-ically. the addition may occur in the syn or the anti mode. In open-chain alkenes (with the exception of terminal alkenes for which stereochemistry is irrelevant), syn hydroxylation transforms cis alkenes into erythro (or meso) diols and trans alkenes into threo (or dl) diols. anti Hydroxylation of cis alkenes gives threo (or dl) diols, whereas anti hydroxylation of trans alkenes yields erythro (or meso) diols. syn Hydroxylation of cycloalkenes gives cis diols, whereas anti hydroxylation furnishes trans diols (Table I). 

The oldest and still very common cleavage is the reaction of unsaturated compounds with ozone and the subsequent treatment of the ozonides formed (equations 95 and 96). Reduction by strong reducing agents such as complex hydrides gives alcohols [94. Cycloalkenes yield diols [82]. 

Acid-catalyzed epoxide cleavage takes place by back-side attack of] nucleophile on the protonated epoxide in a manner analogous to the fn step of alkene bromination, in which a cyclic bromonium ion is opened 1 nucleophilic attack (Section 7.2). When an epoxycycloalkane is opened 1 aqueous acid, a rans-1,2-diol results, just as a from cycloalkene bromination. 

Intramolecular free radical cyclization of dicarboxylic esters leads to a-hydroxy ketones (acyloins). Reductive coupling of dicarbonyl compounds provides 1,2-diols ipinacols) and further reaction of these yields cycloalkenes (McMurry reaction). These cyclization reactions are especially valuable for the preparation of medium and large rings that are not readily accessible by other methods. 

The great utility of fragmentations, especially those of 1,3-diol monosulfonates, for the construction of functionalized, medium-sized cycloalkenes was developed by Wharton, by applying previous results. In recognition of his important contributions to the chemistry of heterolytic fragmentations of cyclic 1,3-diol derivatives, this reaction type has been referred to in a recent review as the Wharton fragmentation . ... 

The full paper on the conversion of 1,2-diols into alkenes by reduction-elimination of appropriate 1,3,2-dioxaphospholans has appeared (see Organophosphorus Chemistry , Vol. 8, p. 123). 2 method was examined with particular regard to the conversion of cyclodecane- and cyclododecane-1,2-diols into the cycloalkenes, as mixtures of cis- and tmns-isomers, and consists of the treatment of the cyclic ethyl esters or AW-dimethylamides with lithium in liquid ammonia or with Ti-THF. The kinetics of the methanolysis of thiophosphoryl chlorides have been studied. The rather unusual isomerization of 2-hydroxyethyl phosphorothioates (70) yields the 2-mercaptoethyl isomers after several days at room temperature instead of the expected thiono-esters. This observation should be compared with those reported in ref. 83. 

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