Dienes regioselective hydroxylation

The asymmetric dihydroxylation of dienes has been examined, originally with the use of NMO as the cooxidant for osmium [56a] and, more recently, with potassium ferricyanide as the cooxidant [56b], Tetraols are the main product of the reaction when NMO is used, but with K3Fe(CN)6, ene-diols are produced with excellent regioselectivity. The example of dihydroxylation of trans.trans-1,4-diphenyl-1,3-butadiene is included in Table 6D.3 (entry 21). One double bond of this diene is hydroxylated in 84% yield with 99% ee when the amounts of K3Fe(CN)6 and K2C03 are limited to 1.5 equiv. each. Unsymmetrical dienes are also dihydroxy-lated with excellent regioselectivity. In these dienes, preference is shown for (a) a bans over a cis olefin, (b) the terminal olefin in a,p,y,8-unsaturated esters, and (c) the more highly substituted olefin [56b],... 

With careful choice of reagent and reaction conditions, alkenes containing other functionalities can be selectively hydroxylated without complicating side reactions. For example, the oxidation may be carried out in the presence of ester, ether, sulfide, carboxylic acid, acetal, carixxiyl, halo, alcohol and aryl groups. Regioselective hydroxylation is also possible in dienes in which one center is electron poor, and some selectivity is also found between isolat double bonds. For example, syn hydroxylatitm of diene... 

Another example, in which the piperidine cycle is generated de novo, exploits a hetero Diels-Alder cycloaddition of 1 -/r-tolylsulfinyl-1,3-penta-diene 91 with benzylnitrosoformate, that generates an oxazine 92 with complete regioselectivity and 7i-facial diastereoselectivity.69 Osmilation of the double bond inserts stereoselectively two hydroxyl groups on the oxazine skeleton, protection and catalytic hydrogenation finally afforded the enantiomerically pure imino sugars 94 (Fig. 38). 

The regioselectivity of the allylation depends on the presence of an adjacent free hydroxyl group the predominant formation of linear 1,4-dienes (awti-Markovnikov products) is achieved from propargylic alcohols whereas simple terminal alkynes wifh a protected hydroxyl group give fhe corresponding branched 1,4-dienes (Markovnikov products) (Tab. 8.9) [57c]. 

Diels-Alder Reactions. Bp3-OEt2 is used to catalyze and reverse the regiospecificity of some Diels-Alder reactions, e.g. with pen-hydroxylated naphthoquinones, sulfur-containing conpounds, the reaction of 1-substituted trans-1,3-dienes with 2,6-dimethylbenzoquinones, and the reaction of 6-inethoxy-l-vinyl-3,4-dihydronaphthalene with p-quinones. BFs-OEta has a drastic effect on the regioselectivity of the Diels-Alder reaction of quinoline- and isoquinoline-5,8-dione with piperylene, which produces substituted azaanthraquinones. This Lewis acid is the most effective catalyst for the Diels-Alder reaction of furan with methyl acrylate, giving high endo selectivity in the 7-oxabicyclo[2.2.1]heptene product (eq 35). ... 

The regioselective complexation of D-mannitol, -galactitol, -xylitol, -ribitol and -erythritol with bis(phosphlne)platinum(II) carbonate complexes has been studied, and conformational analyses of the products by H n.m.r have been performed. Also a study on the preferred conformations of hex-l,S-dien-3,4-diols, which includes reference to hydroxylation reactions, suggesting an approach to hexitol and higher alditol syntheses has been reported. ... 

Iwata, C, Takemoto, Y., Nakamura, A., and Imanishi, T., Oxidation of 2-trimethylsiloxy-1,3-dienes with triphenyl phosphite ozonide. A regioselective a -hydroxylation of a,P-unsaturated ketones. Tetrahedron Lett., 26, 3227, 1985. 

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