Sharpless epoxidation anionic

Sachtler proposes a "dual site" mechanism where the hydrogen is dissociated on the Ni surface and then migrates to the substrate which is coordinated to the adsorbed nickel-tartrate complex. In this context it is of interest that the well known Sharpless epoxidation probably takes place on a dimeric tartrate complex of Ti. Sachtler suggests that both the anion and the cation have a function which varies according to the conditions used. It is not clear whether the spillover mechanism is also proposed for the reaction in solution [55]. 

The synthesis of 132, starting from S-benzyloxy propanal (131), involved the ring opening of an optically active epoxide 133 with a xanthate anion (Scheme 37)J22 Stereoselective synthesis of 133 by Sharpless epoxidation allowed preparation of the 2-deoxy-4-thio-D- and L-ezyr/zro-pentoses, " which were transformed into the corresponding pyrimidine nucleosides with silylated uracil and McaSiOTf. and then deprotected with Bu NF. 

The products of a Sharpless epoxidation, such as epoxides 12, 16, or 22, are potentially unstable in base as the anion of the alcohol can attack the epoxide 24 in the Payne rearrangement. This is easily seen with the simplest compound 12. It doesn t and we have rather given the game away by the compound numbers. The OH groups in the right hand and in the left hand compounds 12 are homotopic. Sharpless made the definitive statement of this in his propranolol synthesis.6... 

Similarly, a C-aryl heptose sugar is prepared for the first time from the diol obtained from ascorbic acid. The epoxide (40), made from the diol (39), on reaction with acetylenic anion and further transformations gave the olefinic alcohol (42). Sharpless epoxidation of 42 and cyclization furnished the C-aryl heptose sugars (43a and 43b) in an efficient way (Scheme 22.10). 

The segment 146 was prepared from L-serine through the methyl ketone 145. The segments 148 and 150 were prepared from alcohols 147 and 149, both of which were derived through Sharpless epoxidation and methylation. The segment 146 was treated with the anion of 148 followed by reductive desulfurization... 

One of the many useful applications of anions of vinyl cyanohydrins, derived from a.jS-unsaturated aldehydes, is in the spiro-lactonization of cyclic ketones for example, cyclohexanone can be converted into (71) in 60% isolated yield. The a-aminonitrile analogues of the cyanohydrins can be used in much the same way. The same spiro-lactonization of ketones can also be carried out using trimethylsilylallylzinc chloride followed by Sharpless epoxidation, hydrolysis, and oxidation, or by using dianions derived from phosphorodiamidates. ... 

R,8S)-(+)-Disparlure (12) is the female sex pheromone of the gypsy moth (Lymantria dispar). Advent of Sharpless asymmetric dihydroxylation (AD) allowed several new syntheses of 12 possible. Sharpless synthesized 12 as shown in Scheme 17 [27]. Scheme 18 summarizes Ko s synthesis of 12 employing AD-mix-a [28]. He extended the carbon chain of A by Payne rearrangement followed by alkylation of an alkynide anion with the resulting epoxide to give B. Keinan developed another AD-based synthesis of 12 as shown in Scheme 19 [29]. Mit-sunobu inversion of A to give B was the key step, and the diol C could be purified by recrystallization. 

Further variations on the epoxyketone intermediate theme have been reported. In the first (Scheme 9A) [78], limonene oxide was prepared by Sharpless asymmetric epoxidation of commercial (S)-(-)- perillyl alcohol 65 followed by conversion of the alcohol 66 to the crystalline mesylate, recrystallization to remove stereoisomeric impurities, and reduction with LiAlH4 to give (-)-limonene oxide 59. This was converted to the key epoxyketone 60 by phase transfer catalyzed permanganate oxidation. Control of the trisubstituted alkene stereochemistry was achieved by reaction of the ketone with the anion from (4-methyl-3-pentenyl)diphenylphosphine oxide, yielding the isolable erythro adduct 67, and the trisubstituted E-alkene 52a from spontaneous elimination by the threo adduct. Treatment of the erythro adduct with NaH in DMF resulted... 

In the case of alkenes with polar functional groups, two-site attachment of the substrate to a chiral oxidant is possible and has allowed spectacular enantioselection. Thus, both the hydroperoxide anion based epoxidation of a,/ -unsaturated carbonyls and the epoxidation of allylic alcohols by the titanium(IV)-based Sharpless method exhibit very high enantioselectivity on a wide variety of substrates. 

Selenides and selenolate anions are usually less basic and more nucleophilic than corresponding sulfur compounds. This unique property was recognized in 1973 by Sharpless and Lauer and used for the conversion of epoxides into allylic alcohols [18]. This publication can be regarded as another milestone in organoselenium chemistry. New aspects and a variety of other related reactions are summarized by M. Iwaoka and S. Tomoda in Chap. 3. 

Preparation of the hydroxypentanoic acid fragment was initiated by addition of the protected propargyl alcohol anion 109 to ethylene oxide. After silylation of the resulting alcohol, the ethoxy ethyl group was removed and the alkyne partially reduced to afford the (2)-alcohol 110 in 52% overall yield. Enantiospecific epoxidation of 110 under Sharpless s conditions and subsequent oxidation provided a 69% yield of diastereomerically pure epoxy acid 111. Treatment with trimethylaluminum gave almost exclusively the p-methyl acid, which was acylated to afford 112 (78%). 

Sharpless and Kim reported a one-pot synthesis of cyclic sulfates 96 from 1,2-diols via catalytic oxidation with ruthenium chloride51. The cyclic sulfates 96 thus formed on treatment with nucleophiles give /2-sulfates 97, which in turn are hydrolyzed to the / -hydroxy compounds 98 (equation 54). Hence the cyclic sulfates 96 are synthetically equivalent to epoxides. The results of ring opening of cyclic sulfates 96 are shown in Table 4. When the reaction of 99 with malonate anion is carried out in DME, the /2-sulfate moiety serves as a leaving group to give cyclopropane 100 (equation 55)51. 

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