Hydroxyl groups vicinal

Reaction of 1-nitropropane with glutaraldehyde in aqueous ethanol in the presence of sodium hydroxide yields a mixture of two products, the major component of which, lr-ethyl-l-nitrocyclohexane-2c,6f-diol (98), can be isolated in 36% yield ). Acid-catalyzed acetylation converts (98) into the di-O-acetate, hydrogenation yields the corresponding amine, which has been characterized as the hydroacetate, N-acetate and triacetate. Configurational assignments followed from NMR data, which clearly showed the steric non-equivalence of the two hydroxyl groups vicinal to the tertiary center. 

The fluorine NMR spectrum of l,l,l-trifluoro-2-propanol (Figure 5.5) provides an example of a compound with a hydroxyl group vicinal to a CF3 group. 

This method appears to be of general application for the synthesis of amino sugars with the cis configuration of hydroxyl groups vicinal to amino groups. The synthesis of all of the theoretically possible 2-amino-2-deoxy-,... 

According to the theory, the initial reaction is the formation of an alk-oxide (I) between the base and the sugar hydroxyl group vicinal to the carbonyl group. A molecule of base is then eliminated, to give the free, methylenic intermediate (II). The latter isomerizes to the epoxy compound (III) and thence to the a-dicarbonyl intermediate (IV). Finally, a benzilic acid type of rearrangement, with hydration and dismutation, gives the saccharinic acid. 

Dioxolane-type ndo-benzylidene acetals were the main products in the kinetically controlled reactions of several hexopyranosides carrying 2,3- or 3,4-cis-hydroxyl groups with dimethoxytoluene and p-tolenesulfonic acid without added solvent. It was noted that endo-exo isomerization was faster for derivatives with unprotected hydroxyl groups vicinal to the acetal thus, methyl a-L-ihanuiopyranoside gave a 1 1 mixture of 14 and 15, while from the 4-0-benzylated starting conqx>und the endo-product 16 was formed stereospecifically. ... 

In aqueous solution chlorine and bromine react with alkenes to form vicinal halohy drins, compounds that have a halogen and a hydroxyl group on adjacent carbons... 

Vicinal diols are diols that have their hydroxyl groups on adjacent carbons Two commonly encountered vicinal diols are 1 2 ethanediol and 1 2 propanediol... 

Halohydrin (Section 6 17) A compound that contains both a halogen atom and a hydroxyl group The term is most often used for compounds in which the halogen and the hydroxyl group are on adjacent atoms vicinal halohydrins) The most commonly encountered halohydrins are chlorohydnns and brornohydrins... 

Study of the mechanism of this complex reduction-Hquefaction suggests that part of the mechanism involves formate production from carbonate, dehydration of the vicinal hydroxyl groups in the ceUulosic feed to carbonyl compounds via enols, reduction of the carbonyl group to an alcohol by formate and water, and regeneration of formate (46). In view of the complex nature of the reactants and products, it is likely that a complete understanding of all of the chemical reactions that occur will not be developed. However, the Hquefaction mechanism probably involves catalytic hydrogenation because carbon monoxide would be expected to form at least some hydrogen by the water-gas shift reaction. 

In a similar way, 5-O-acetylthymidine was converted into the 3-deoxy-3-iodo derivative 72 in 55% yield. In this case, the replacement of the hydroxyl group by iodine was presumed to have taken place by retention of the configuration at C-3. The first intermediate in the reaction was proposed to be the phosphonate (70) which rapidly collapses to an O-3-cyclonucleoside (71) and the latter is subsequently attacked by iodide ion to give the product 72. It was also observed (106) that treatment of nucleosides containing a cis vicinal diol grouping such as 5-0-acetyluridine with triphenylphosphite methiodide failed to provide iodinated products but gave phosphonate derivatives instead. 

From intermediate 12, the path to key intermediate 7 is straightforward. Reductive removal of the benzyloxymethyl protecting group in 12 with lithium metal in liquid ammonia provides diol 27 in an overall yield of 70% from 14. Simultaneous protection of the vicinal hydroxyl groups in 27 in the form of a cyclopentanone ketal is accompanied by cleavage of the tert-butyldimethylsilyl ether. Treatment of the resultant primary alcohol with /V-bromosuccini-mide (NBS) arid triphenylphopshine accomplishes the formation of bromide 7, the central fragment of monensin, in 71 % yield from 27. 

Scheme 6a presents the synthesis of fragment 15. Intermediate 15 harbors two vicinal stereogenic centers, and is assembled in a very straightforward manner through the use of asymmetric aldol methodology. Treatment of the boron enolate derived from 21 with 3-[(p-methoxybenzyl)oxy]propanal (22) affords crystalline syn aldol adduct 34 in 87 % yield as a single diastereomer. Transamination to the A-methoxy-A-methylamide,20 followed by silylation of the secondary hydroxyl group at C-19 with triethylsilyl chloride, provides intermediate 15 in 91 % yield. 

Vicinal hydroxyl groups, as in an ethylene glycol unit, have conformational attributes that can be described by using acyclic orientational notation... 

In the pyranoses in the chair conformations, the vicinal hydroxyl groups can exist only in the anticlinal or gauche orientations. The gauche arrangement of a-glycols is normally encountered as diequatorial or axial-... 

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