Dienes hydroxylation

Erikson JR, Zimmerman EM. Non aqueous solvent-free process for making UV-curable adhesives and sealants from epoxidized mono-hydroxylated diene polymers. World patent WO 0181494, CA] 2001 2001-798358. 

A most careful study was now carried out by NMR spectroscopy, not only by regular Ih 500 MHz and 13C but also by 1H COSY NMR spectroscopy [4,5). Individual compounds were isolated by preparative HPLC of the mixture in urushiol, particularly of kuro-urushi and all the isomers, including the cis-trans isomers were identified and characterized [Figure 4] [5). Particular care was taken to identify the water addition product [M]K" =371 daltons. It was found that water had indeed been added to the triene to form a C10 hydroxylated diene [Formula] [5]. This water addition is catalyzed by some additives such as ferric chloride which are used in the sugurome process to optimize the lacquer properties. The details of the process is a closely guarded secret and is slightly different from manufacturer to manufacturer. 

P-Hydroxy steroids which contain the 5,7-diene system and can be activated with uv light to produce vitamin D compounds are called provitamins. The two most important provitamins are ergosterol (1) and 7-dehydrocholesterol (3). They are produced in plants and animals, respectively, and 7-dehydrocholesterol is produced synthetically on a commercial scale. Small amounts of hydroxylated detivatives of the provitamins have been synthesized in efforts to prepare the metaboHtes of vitamin D, but these products do not occur naturally. The provitamins do not possess physiological activities, with the exception that provitamin D is found in the skin of animals and acts as a precursor to vitamin D, and synthetic dihydroxalated... 

Treatment of the 9-fiuoro-l,4-dien-3-ol (15) with 3.5 g-atoms of lithium and l-methoxy-2-propanol in ammonia reductively cleaves the allylic 3-hydroxyl group to give t7 corresponding 3-desoxy compound, but the fluorine... 

A -dien-3-ol ethers gives rise to 6-substituted A" -3-ketones. 6-Hydroxy-A" -3-ketones can be obtained also by autooxidation.Structural changes in the steroid molecule may strongly affect the stability of 3-alkyl-A -ethers. Thus 11 j5-hydroxyl and 9a-fluorine substituents greatly increase the lability of the enol ether/ while halogens at C-6 stabilize this system to autooxidation and acid hydrolysis. 

Allylic A" -3-hydroxyls are particularly reactive, although some difficulty arises because this system is prone to acid-catalysed dehydration to the 3,5-diene. A" -3-Methyl ethers are readily prepared by direct, p-toluenesulfonic acid-catalysed reaction with methanol. 

An unprotected 3-hydroxyl group does not significantly lower the yield, but an 11 j5-hydroxyl has an adverse effect, and no product is obtained in the presence of a free 21-hydroxyl group. An isolated double bond at C-5 does not seriously interfere /,/-20-cyano-3,3-ethylenedioxy-21-hydroxypregna-5,17 (20)-dien-l l-one acetate gives 89% of the 17a-hydroxy-20-ketone. ... 

The result of oxidation of 8-hydroxy-2,3-tetrafluorobenzobicyclo[3 2 l]octa-2,6-diene depends on the configuration of the hydroxyl group In the syn isomer, the double bond is not epoxidized by the Jones reagent [5/] (equation 52)... 

For the construction of oxygen-functionalized Diels-Alder products, Narasaka and coworkers employed the 3-borylpropenoic acid derivative in place of 3-(3-acet-oxypropenoyl)oxazolidinone, which is a poor dienophile in the chiral titanium-catalyzed reaction (Scheme 1.55, Table 1.24). 3-(3-Borylpropenoyl)oxazolidinones react smoothly with acyclic dienes to give the cycloadducts in high optical purity [43]. The boryl group was converted to an hydroxyl group stereospecifically by oxidation, and the alcohol obtained was used as the key intermediate in a total synthesis of (-i-)-paniculide A [44] (Scheme 1.56). 

Geranyl acetate (a diene) takes up 2 moles of hydrogen unselectively in 48 hours to give the saturated acetate, 3,7-dimethyloctyl acetate, bp 109-110712 mm, 1.4261. (Geraniol itself has an allylic hydroxyl and appears to suffer decarbonylation under these reaction conditions.)... 

Hydroformylation of nitrile rubber is another chemical modification that can incorporate a reactive aldehyde group into the diene part and further open up new synthetic routes to the formation of novel nitrile elastomers with a saturated backbone containing carboxyl or hydroxyl functionalities. 

The aldehyde function at C-85 in 25 is unmasked by oxidative hydrolysis of the thioacetal group (I2, NaHCOs) (98 % yield), and the resulting aldehyde 26 is coupled to Z-iodoolefin 10 by a NiCh/CrCH-mediated process to afford a ca. 3 2 mixture of diaste-reoisomeric allylic alcohols 27, epimeric at C-85 (90 % yield). The low stereoselectivity of this coupling reaction is, of course, inconsequential, since the next operation involves oxidation [pyridinium dichromate (PDC)] to the corresponding enone and. olefination with methylene triphenylphosphorane to furnish the desired diene system (70-75% overall yield from dithioacetal 9). Deprotection of the C-77 primary hydroxyl group by mild acid hydrolysis (PPTS, MeOH-ClHhCh), followed by Swem oxidation, then leads to the C77-C115 aldehyde 28 in excellent overall yield. 

Unsaturated polyesters were obtained by reacting the glycolyzed product widi maleic anhydride at a hydroxy-to-carboxyl ratio of 1 1. The hydroxyl number was determined without separation of die free glycol. The polyesterification reaction was conducted in a 2-L round-bottom dask equipped with a condenser, a gas bubbler, a thermowell, and a stirrer. The reaction mixture was heated from room temperature to 180°C in about 1-1.5 h. The temperature was maintained at 180°C for about 3 h, dien raised to 200°C and maintained until die acid value reached 32 mg KOH/g. 

Hoomaert has studied Diels-Alder reactions of pyridine oquinodimethane analogs generated from functionalized o-bis(chloromethyl)pyridines <96T(52)11889>. The photochemical cycloaddition of 2-alkoxy-3-cyano-4,6-dimethylpyridine with methacrylonitrile gives a bicyclic azetine, 6-alkoxy-3,5-dicyano-2,5,8-trimethyl-7-azabicyclo[4.2.0]octa-2,7-diene, in moderate yield <96CC1349>. Regiospecific hydroxylation of 3-(methylaminomethyl)pyridine to 5-(methylaminomethyl)-2-(17/)-pyridone by Arthrobacter ureafaciens has been reported <96MI173>. 

The zirconocene catalysts described above are very oxophilic, which provides several synthetically useful transformations. Oxygen substitution at the al-lylic or homoallylic position of an olefin substrate allows for excellent regio-and diastereocontrol in the ethyl magnesiation reactions of a-olefins and dienes [21]. When 29 is substituted with a hydroxyl group (29a), syn 30a is favored over anti in a 95 5 ratio, while substitution with OCH3 (29b) reversed the diastereoselectivity to 11 89 (Eq. 6). Use of THF in place of diethyl ether as the reaction solvent for the reaction of 29a lowered the overall diastereo-... 

Selenium dioxide is also an oxygen donor to alkenes. In this case, however, the initial reaction of the double bond is with the selenium center followed by two pericyclic steps. After hydrolysis of the organo-selenium intermediate, the result is a hydroxylation at the allylic carbon position65. Thus, limonene (2) yields racemic p-mentha-l,8(9)-dien-4-ol66. The high toxicity of selenium intermediates and prevalence of many rearrangements has limited the widespread use of the reagent in synthesis. 

A nice and convergent approach to both compounds makes use of RCM to form the 5-membered building block 71, which mimics the carbohydrate part of the nucleosides. The necessary diene precursor 69 is readily assembled via Evans aldol chemistry. RCM then affords the ring in almost quantitative yield (69->70), leaving the chiral centers and the free hydroxyl group intact. Removal of the chiral auxiliary by reductive cleavage, attachment of the base by means of jt-allylpalladium chemistry, and a final deprotection step complete these highly efficient syntheses [46]. 

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