1.2- Diols, from alkene hydroxylations

The Woodward Reaction (or Woodward c/s-Hydroxylation) allows the synthesis of syn-diols from alkenes by the addition of iodine followed by nucleophilic displacement with acetate in the presence of water. Hydrolysis of the intermediate ester gives the desired diol. The Prevost Reaction gives crn/z -diols. 

Hydroxylation synthesis of 1,2-diols from alkenes (Sections 8-13 and 8-14)... 

Alkenes are reduced by addition of H2 in the presence of a catalyst such as platinum or palladium to yield alkanes, a process called catalytic hydrogenation. Alkenes are also oxidized by reaction with a peroxyacid to give epoxides, which can be converted into lTans-l,2-diols by acid-catalyzed epoxide hydrolysis. The corresponding cis-l,2-diols can be made directly from alkenes by hydroxylation with 0s04. Alkenes can also be cleaved to produce carbonyl compounds by reaction with ozone, followed by reduction with zinc metal. 

Exercise 16-37 An elegant modification of the two-step procedure to prepare ketones from alkenes by hydroxylation and oxidative cleavage of the diol formed uses a small amount of potassium permanganate (or osmium tetroxide, 0s04) as the catalyst and sodium periodate as the oxidizing agent ... 

Acetaldehyde has been prepared in part (a). Recalling that vicinal diols are available from the hydroxylation of alkenes, 1,2-ethanediol may be prepared by the sequence... 

The diol can be prepared from syn hydroxylation of (Z)-2-butene. The c/s-alkene can be prepared by hydrogenation of 2-butyne, and 2-butyne can be prepared by alkylation of propyne. The retrosynthetic analysis is ... 

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... 

The hydroxylation of alkenes to diols with potassium osmate-oxidant mixtures has been described, with either hydrogen peroxide or sodium chlorate as the oxidant. The sodium chlorate method is not applicable where the diol is to be distilled from the mixture, because of the danger of explosive oxidation of the product diol by the chlorate. 

In their pioneering work. Just and co-workers have described many interesting transformations of the Diels-Alder adducts of furan to methyl nitroacrylate (77 + 77 ) and to dimethyl acetylenedicarboxylate (53). The mixture of racemic adducts 77 + 77 was hydroxylated into the exo-cis-diols 125 + 125 , separable by crystallization. Treatment of the isopropylidene acetal obtained from 125 with diazabicyclo[5.4.0]undec-5-ene (DBU) gave a high yield of alkene 126. Ozonolysis followed by a reductive work-up with dimethylsulfide, then with NaBH4, gave a mixture of epimeric triols 127. Cleavage with sodium periodate afforded 2,5-anhydro-3,4-0-isopropylidene-DL-allose (128) in 15 % yield, based on methyl 2-nitroacrylate used. TTie same allose derivative was obtained from adduct 53. ... 

Optically active ds.vic-diofa.1 It is known that pyridine catalyzes the hydroxyl-ation of alkenes with Os04 and that the osmate ester intermediates form an isolable complex with pyridine (1, 760-761). Hentges and Sharpless reasoned that a similar chiral amine could induce chirality in the diol. And indeed addition of 1 equivalent of 1 or of the C8-diastereoisomer, dihydroquinidine acetate (2), does result in vic-diols in fair to high enantiomeric excess, particularly in reactions performed in toluene at —78°. Opposite stereoselectivities are exhibited by 1 and 2. Optical yields range from 25 to 85%. Use of an amine in which the chiral center is two carbon atoms removed from the coordination site lowers the optical yield to 3 18%. 

Spiro acetals can also be stereoselectively hydroxylated, in high yield, with osmium tetraoxide and a catalyst. The resultant diol is formed by. vyw-hydroxylation from the least hindered side of the alkene moiety (equation 21)121. 

Hydroxylation of an alkene may be carried out using osmium tetroxide in an inert solvent (e.g. ether or dioxane), whereupon a cyclic osmate ester is formed. This undergoes hydrolytic cleavage under reducing conditions (e.g. aqueous sodium sulphite) to give the 1,2-diol resulting from a ds-hydroxylation process.71... 

A 1,2-diol arising from a trans-hydroxylation process is formed from an alkene by way of an intermediate epoxide which is subjected to a ring-opening reaction and hydrolysis. The epoxides may be isolated when the alkene is reacted with perbenzoic add or m-chloroperbenzoic acid (Section 4.2.56, p. 457) in a solvent such as chloroform or dichloromethane the preparation of epoxides by this method and by other important procedures are discussed and illustrated... 

Alkenes and Potassium Osmate. Sodium chlorate should not be used in the hydroxylation of alkenes to diols in the presence of potassium osmate if the diol is to be distilled from the reaction mixture explosive oxidation may occur.3... 

Alkenes from diols. Reaction of v/c-diols with two secondary hydroxyls or one primary and one secondary alcohol with chlorodiphenylphosphine (2 equiv.), imidazole (4 equiv.), and iodine (2 equiv.) results in alkenes. The reaction presumably involves a vic-iododiphenylphosphinate, which can be isolated in some cases and converted to an alkene with zinc in acetic acid. 

The aminocyclitol moiety was synthesized in a stereocontrolled manner from cis-2-butene-l,4-diol (Scheme 40)112 by conversion into epoxide 321 via Sharpless asymmetric epoxidation in 88% yield.111 Oxidation of 321 with IBX, followed by a Wittig reaction with methyl-triphenylphosphonium bromide and KHMDS, produced alkene 322. Dihydroxylation of the double bond of 322 with OSO4 gave the diol 323, which underwent protection of the primary hydroxyl group as the TBDMS ether to furnish 324. The secondary alcohol of 324 was oxidized with Dess-Martin periodinane to... 

Substituents occupying sites more remote from the alkenic center than the allylic position may also influence the direction of attack on an alkene with diastereotopic Tr-faces. Thus, cyclic alkenes with a sul-foximine group attached to an exocyclic homoallylic carbon atom and a hydroxy group at the allylic position, for example (Iti) in equation (5), undergo syn hydroxylation with a very high degree of dia-stereoselectivity, diol (17) being produced as the sole diastereoisomer. ... 

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