Jones oxidation allylic alcohols

The next step in the Sih sequence involved oxidation of the allylic alcohol and the a.p-unsaturated aldehyde to the keto acid VII, which was accomplished by simultaneous oxidation with the Jones... 

Namely, allyl alcohol is successively treated with diethylzinc, (R,R) dipropyl tartrate, and 4-methoxybenzohydroximinoyl chloride (163) to afford the enantiomeric isoxazoline alcohol 166, which under the Jones oxidation conditions affords the corresponding carboxylic acid derivative (167). Treatment of compound 167 with hydroxylamine-O-triflate followed by tri-fluoroacetic acid gives rise to the desired enantiomeric 165 in high excess enantiomeric yield. The synthesis of other isosteric analogues of 165 was reported in the same paper. None of the isosteric analogues exhibits LpxC inhibitory and antibacterial activities [103]. 

Nevertheless, in those cases in which the proportion of hydrate in equilibrium with the aldehyde is low, it is possible to obtain a useful yield of aldehyde.60,61 Electron donating groups,68,69 conjugation with alkenes and aromatic rings5 and steric hindrance69 decrease the proportion of hydrates in equilibrium with aldehydes. This explains the fact that alcohols successfully transformed into aldehydes by Jones oxidation, normally belong to the allyl,70 benzyl71 or neopentyl kind.72... 

As the Jones-mediated transformation of tertiary allylic alcohols into enones is normally slower than the oxidation of secondary alcohols into ketones it is possible to selectively oxidize a secondary alcohol to ketone, without affecting a tertiary allylic alcohol present in the same molecule. 

Similar to Jones reagent, Collins reagent can produce a hydroxy directed epoxidation of allylic alcohols. This side-reaction only occurs in a limited number of allylic alcohols, most of them being oxidized uneventfully to the corresponding enones.117... 

Quite unsurprisingly, apart from stereoelectronic factors, DDQ oxidation of unsaturared alcohols is also subject to steric factors. For instance, the highly hindered allylic alcohol 94 could not be oxidized with DDQ in benzene at room temperature, being necessary to employ Jones oxidation.103... 

Secondary alcohols give good yields of ketones, but the foremost use of the Jones oxidation has been for the conversion of saturated primary alcohols to the corresponding acid. In direct contrast, primary allylic and benzylic alcohols can be selectively oxidized to aldehydes acids are obtained only after prolonged exposure to the oxidant. In rigid systems it has been found that axial alcohols are oxidized faster than equatorial alcohols. "... 

Large scale epoxidation of 53 (50-100 g) with peracetic acid (33) consistently furnished the epoxides 54 and 55 in essentially quantitative yield. Treatment of the epoxides (40-100 g) with sodium ethoxide in refluxing ethanol provided allylic alcohol 56. Oxidation of 56 (0.50 mmol-0.50 mol) with the Jones reagent (13,34) consistently afforded enone 57 in yields of 95 or "Better. In large scale conversions of 53 to 57, the crude intermediate compounds 54, 55, and 56 were used directly in the subsequent reaction without further purification. Typically, for the three-step process, 57 is obtained in 95 yield, sufficiently pure for the next reaction. 

Radical addition of triphenylgermane to vinyl oxiranes proceeded in the presence of triethylborane to yield 4-triphenylgermyl-2-buten-l-ol derivatives in good yield. Iodo acetals, prepared by iodoetherification of vinyl ethers with the allylic alcohol, underwent radical cychzation to give 2-alkoxy-4-vinyltetrahydrofurans which were converted into 4-vinyltetrahydro-2-furanones by Jones oxidation (Scheme 11.22) [38]. 

Jones reagent [1, 143, after citation of ref. 7] Lavie el al.n treated the steroidal lactone (1) with the Jones reagent expecting to obtain the corresponding enone. Instead they obtained the epoxy diketone (2). The same product was also obtained from the isomeric allylic alcohol (3). Further investigation established that epoxi-dation occurs only if the hydroxy] group is axial, and if the oxidation is slower than... 

Two-phase oxidation [1, 143, last paragraph]. Allylic alcohols (1) are oxidized to the corresponding vinyl ketones (2) in acceptable yields by the procedure of Brown and Garg.11 A 30-40% excess of oxidant is required because of concurrent oxidation at the double bond.113 The Jones reagent is less satisfactory. 

Enantiomerically pure samples of / -vinyI- -butyrolactone (98) were prepared starting from the diastereomerically pure bromoacetal 96 (obtained by separation of the 1 1 mixture of products from the corresponding vinyl ether, 1,2-butadiene-4-ol, and NBS) via purification of the major cyclization product 97. The bromoacetal obtained from 1-ethoxypropene was used in an approach to the dihydroagarofuran framework [66]. Bridged pyranosides were synthesized from cyclic iodoacetals [67]. Bicyclic acetals may be prepared with relative ease epialboatrin (100) was synthesized via a successful hypophosphite-mediated radical cyclization of the cyclic bromohydrin 99 [68] (Scheme 35). In one of the early examples reported by Ueno, bromoacetals obtained from butoxyallene, allylic alcohols, and NBS underwent efficient radical cyclization reactions providing easy access to a-methylene-y-butyrolactones after Jones oxidation [69]. 

Allylic alcohol 6.92 was prepared in about seven steps from tartaric acid and once in hand, treatment with sodium hydride and benzyl bromide gave 6.93. Hydro-boration of the alkene moiety and Jones oxidation of the resultant alcohol gave a carboxylic acid 6.94). Deprotection and ring opening gave R-GABOB. ... 

A Shapiro reaction reduces the ketone 74 into the allylic alcohol 75. After Jones oxidation, the y-lactone 76 is alkylated stereoselectively at Cll to give the target molecule 65. 

The structure of ( —) 2P-acetoxy-1 la-hydroxyverrucosane (544) was established as follows (Scheme 65). Jones oxidation of (544) gave a five-membered ketone (551). Acid treatment of the latter resulted in homoallylic ring expansion to homo-allylic ketoalcohol (552) which was converted via the tosylhydrazone into (548) identical with the homoallylic alcohol prepared from (547) via (545) (Scheme 64). That the 11-hydroxyl group was a was inferred from the remarkable downfield shifts exhibited by the C-10 and the C-12 methyl groups of the five-membered ketone (551) and the small solvent shift exhibited by the C-10 methyl group (553) and its homoallylic ring expanded product. 

Steroidal 7t-allyl complexes can be oxidatively cleaved to allyl alcohols with high stereoselectivity (Jones and Knox, 1975b). For example, the n-allyl palladium chloride dimer, XIV, derived from cholest-4-ene, undergoes bridge cleavage by pyridine and then oxidation by w-chloroperbenzoic acid to give XVI as the sole product. Similar reaction of the isomeric Jt-allyl... 

The oxidation of primary alcohols with K2Cr207 in aqueous solution to nothing but the aldehyde, (i.e., without further oxidation to the carboxylic acid) is possible only if a volatile aldehyde results and is distilled off as it is formed. This is the only way to prevent the further oxidation of the aldehyde in the (aqueous) reaction mixture. Selective oxidations of primary alcohols to aldehydes with the Jones reagent succeed only for allylic and benzylic alcohols. Otherwise, the Jones reagent directly converts alcohols into carboxylic acids (see above). 

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