Hydroxylation 16,17-Diols

Dehydrogenation with selenium dioxide gives the l,4-dien-3-one (19-1). The great majority of such glycols are commonly used as their 16,17-cyclic acetals with some small ketone. In the case at hand, reaction with acetone gives the acetal 19-2, that group often being called an acetonide. 

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Figure 6A Chromatographic separation, of the Neutrals fractions from the Light and Medium Dark Lithotypes. Numbers directly above eluted peaks identify the chain length of these even n-alcohols. Numbers below the chromatogram refer to the carbon chain length of the corresponding terminally hydroxylated diols. (X) is identified as 1,9-dihydroxy-dodecane.

The acetonide is cleaved under mild acidic conditions with catalytic amounts of / -toluene sulfonic acid, releasing hydroxyl diol 42. Performing the reaction in ethanol leads to an acetal exchange process, whose mechanism is analogous to the THP acetal cleavage presented earlier. 

C21H36O2. M,p. 238°C. There are four isomeric pregnane-3,20-diols differing only in the orientation of the hydroxyl groups at positions 3 and 20 and with the 5/ configuration. Only the 3a,20a occurs naturally. It is formed by reduction of progesterone in the liver and is the chief urinary metabolite of it, being... 

A good approach to 1,2-diols is hydroxylation of an olefin with reagents such as OSO4 or KMn04. The olefin can be made by the Wittig reaction so the discoimections arc ... 

The benzylidene derivative above is used, if both hydroxyl groups on C-2 and C-3 are needed in synthesis. This r/vzns-2,3-diol can be converted to the sterically more hindered a-cpoxide by tosylation of both hydroxy groups and subsequent treatment with base (N.R. Williams, 1970 J.G. Buchanan, 1976). An oxide anion is formed and displaces the sulfonyloxy group by a rearside attack. The oxirane may then be re-opened with nucleophiles, e.g. methyl lithium, and the less hindered carbon atom will react selectively. In the following sequence starting with an a-glucoside only the 2-methyl-2-deoxyaltrose is obtained (S. Hanessian, 1977). 

We 11 Start by discussing m more detail a class of compounds already familiar to us alcohols Alcohols were introduced m Chapter 4 and have appeared regularly since then With this chapter we extend our knowledge of alcohols particularly with respect to their relationship to carbonyl containing compounds In the course of studying alco hols we shall also look at some relatives Diols are alcohols m which two hydroxyl groups (—OH) are present thiols are compounds that contain an —SH group Phenols, compounds of the type ArOH share many properties m common with alcohols but are sufficiently different from them to warrant separate discussion m Chapter 24... 

Much of the chemistry of diols—compounds that bear two hydroxyl groups—is analo gous to that of alcohols Diols may be prepared for example from compounds that con tain two carbonyl groups using the same reducing agents employed m the preparation of alcohols The following example shows the conversion of a dialdehyde to a diol by... 

Diols are almost always given substitutive lUPAC names As the name of the prod uct m the example indicates the substitutive nomenclature of diols is similar to that of alcohols The suffix dwl replaces ol and two locants one for each hydroxyl group are required Note that the final e of the parent alkane name is retained when the suffix begins with a consonant ( diol) but dropped when the suffix begins with a vowel ( ol)... 

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... 

Overall the reaction leads to addition of two hydroxyl groups to the double bond and IS referred to as hydroxylation Both oxygens of the diol come from osmium tetraox ide via the cyclic osmate ester The reaction of OSO4 with the alkene is a syn addition and the conversion of the cyclic osmate to the diol involves cleavage of the bonds between oxygen and osmium Thus both hydroxyl groups of the diol become attached to the same face of the double bond syn hydroxylation of the alkene is observed... 

Cyclic diols give dicarbonyl compounds The reactions are faster when the hydroxyl groups are cis than when they are trans but both stereoisomers are oxidized by periodic acid... 

Diols that bear two hydroxyl groups m a 1 2 or 1 3 relationship to each other yield cyclic acetals on reaction with either aldehydes or ketones The five membered cyclic acetals derived from ethylene glycol (12 ethanediol) are the most commonly encoun tered examples Often the position of equilibrium is made more favorable by removing the water formed m the reaction by azeotropic distillation with benzene or toluene... 

Hydrophilic (Section 19 5) Literally water loving a term applied to substances that are soluble in water usually be cause of their ability to form hydrogen bonds with water Hydrophobic (Section 19 5) Literally water hating a term applied to substances that are not soluble in water but are soluble in nonpolar hydrocarbon like media Hydroxylation (Section 15 5) Reaction or sequence of reac tions in which an alkene is converted to a vicinal diol Hyperconjugation (Section 4 10) Delocalization of a electrons... 

Acetals are readily formed with alcohols and cycHc 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, furfuryUdene diacetate... 

I60C-Hydroxy Derivatives of Gorticoids and their Acetonides. The preparation of 16a-hydroxy-9a-fluoroprednisolone (48) from the 3,20-bisethylene ketal of hydrocortisone acetate (49) has been reported (73). The latter was dehydrated with thionyl chloride in pyridine to yield the 4,9(11),16-triene (50). The 16,17-unsaturated linkage was selectively hydroxylated with OsO /pyridine to yield the 16a,17a-diol (51), which was converted... 

Butenediol. 2-Butene-l,4-diol [110-64-5] is the only commercially available olefinic diol with primary hydroxyl groups. The commercial product consists almost entirely of the cis isomer. 

Diester/Ether Diol of Tetrabromophthalic Anhydride. This material [77098-07-8] is prepared from TBPA in a two-step reaction. First TBPA reacts with diethylene glycol to produce an acid ester. The acid ester and propylene oxide then react to give a diester. The final product, a triol having two primary and one secondary hydroxyl group, is used exclusively as a flame retardant for rigid polyurethane foam (53,54). 

Neopentyl glycol, or 2,2-dimethyl-1,3-propanediol [126-30-7] (1) is a white crystalline soHd at room temperature, soluble ia water, alcohols, ethers, ketones, and toluene but relatively iasoluble ia alkanes (1). Two primary hydroxyl groups are provided by the 1,3-diol stmcture, making this glycol highly reactive as a chemical intermediate. The gem-A methy configuration is responsible for the exceptional hydrolytic, thermal, and uv stabiUty of neopentyl glycol derivatives. 

Following this work, the y -12F-diol was used for the direct reaction with hexamethylene-1,6-diisocyanate in the presence of dibutyltin dilaurate to produce a cross-linked elastomer or a reactive prepolymer which was terminated with either isocyanate or hydroxyl groups, depending on which reactant was in excess (142,143). 

Preparation of the polymer can be carried out in glass equipment at atmospheric pressure at temperatures typically above 100°C, but the higher pressures in an autoclave result in much faster reaction rates. Each polymer molecule which used butanol as a starter contains one hydroxyl end group as it comes from the reactor diol-started polymers contain two terminal hydroxyls. Whereas a variety of reactions can be carried out at this remaining hydroxyl to form esters, ethers, or urethanes, this is normally not done and therefore lubricant fluids contain at least one terminal hydroxyl group (36). 

Diols, such as ethylene glycol, are usually not added during the alcoholysis step because their monoesters have only one remaining hydroxyl group, and would function as chain stoppers, thus severely limiting their utihty in the stmcture design of the resin molecules. 

Titanium chelates are formed from tetraalkyl titanates or haUdes and bi- or polydentate ligands. One of the functional groups is usually alcohoHc or enoHc hydroxyl, which interchanges with an alkoxy group, RO, on titanium to Hberate ROH. If the second function is hydroxyl or carboxyl, it may react similarly. Diols and polyols, a-hydroxycarboxyflc acids and oxaUc acid are all examples of this type. P-Keto esters, P-diketones, and alkanolamines are also excellent chelating ligands for titanium. 

Where the glycol contains one or two secondary or tertiary hydroxyls, the products are more soluble and some are even monomeric cycHc chelates (65,66). Three compounds are obtained from 2-meth5lpentane-2,4-diol, depending on the mole ratio (67—70). Stmcture (3) represents an isolable but labile alcoholate of (2)... 

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