Reaction with dimethyl dioxirane

The cyclohexyloxy(dimethyl)silyl unit in 8 serves as a hydroxy surrogate and is converted into an alcohol via the Tamao oxidation after the allylboration reaction. The allylsilane products of asymmetric allylboration reactions of the dimethylphenylsilyl reagent 7 are readily converted into optically active 2-butene-l, 4-diols via epoxidation with dimethyl dioxirane followed by acid-catalyzed Peterson elimination of the intermediate epoxysilane. Although several chiral (Z)-y-alkoxyallylboron reagents were described in Section 1.3.3.3.3.1.4., relatively few applications in double asymmetric reactions with chiral aldehydes have been reported. One notable example involves the matched double asymmetric reaction of the diisopinocampheyl [(Z)-methoxy-2-propenyl]boron reagent with a chiral x/ -dialkoxyaldehyde87. 

The Diels-Alder reaction outlined above is a typical example of the utilization of axially chiral allenes, accessible through 1,6-addition or other methods, to generate selectively new stereogenic centers. This transfer of chirality is also possible via in-termolecular Diels-Alder reactions of vinylallenes [57], aldol reactions of allenyl eno-lates [19f] and Ireland-Claisen rearrangements of silyl allenylketene acetals [58]. Furthermore, it has been utilized recently in the diastereoselective oxidation of titanium allenyl enolates (formed by deprotonation of /3-allenecarboxylates of type 65 and transmetalation with titanocene dichloride) with dimethyl dioxirane (DMDO) [25, 59] and in subsequent acid- or gold-catalyzed cycloisomerization reactions of a-hydroxyallenes into 2,5-dihydrofurans (cf. Chapter 15) [25, 59, 60],... 

Hamilton, R., McKervey, M.A., Rafferty, M.D., and Walker, B.J., The reaction of dimethyl dioxirane with diazomethylphosphonates. The first synthesis of a formylphosphonate hydrate, J. Chem. Soc., Chem. Commun., 37, 1994. 

Dihydroxylation of benzofuran and benzothiophene giving d5 -2,3-dihydro-2,3-dihydroxy derivatives can be achieved nsing Pseudomonas putida. Benzofurans can be epoxidised at the hetero-ring double bond with dimethyl dioxirane, or alternatively converted into dioxetanes by reaction of that double bond with singlet oxygen. Both oxidised species are unstable and undergo a variety of complex further processes. ... 

Many other reagents for converting alkenes to epoxides,including H2O2 and Oxone , VO(0-isopropyl)3 in liquid C02, ° polymer-supported cobalt (II) acetate and 02, ° and dimethyl dioxirane.This reagent is rather versatile, and converts methylene oxiranes to spiro-epoxides. ° ° One problem with dimethyloxirane is C—H insertion reactions rather than epoxidation. Magnesium monoperoxyphthalate is commercially available, and has been shown to be a good substitute for m-chloroperoxybenzoic acid in a number of reactions. 

The oxidative cyclization of allenyl alcohol 135 with a small excess of dimethyl-dioxirane leads to an intermediate diepoxide that rearranges to hydroxyfuranone 136 in 55% yield (Eq. 13.44) [52]. If the oxidative cyclization is conducted in the presence of 0.5 equiv. of toluenesulfonic acid, the major product is the furanone lacking the a-hydroxy group of 136. Hydroxyfuranones or pyranones are available from the same kinds of reactions of 5-methylhexa-3,4-dien-l-ol. 

Aliphatic primary amines are known to be oxidized by dimethyl dioxiranes to various products such as oximes, nitroso dimers, nitroalkanes, nitrones and oxazrridines under various conditions depending upon the oxidation reaction . In contrast, when secondary amines lacking a-hydrogens are allowed to react with Oxone and PTC in buffered acetone solution at 0 °C, nitroxides are obtained in good yields in a few minutes (equation 61) . 

The same 1,4-dialdehyde can be made by oxidizing furan with the mild oxidizing agent dimethyl-dioxirane, which you met on p. 506. In this sequence, it is trapped in a Wittig reaction to give an E,Z-diene, which is easily isomerized to E,E. 

Many variations of the Rubottom oxidation employ oxidants other than m-CPBA in order to execute the transformation under mild conditions or to allow for enantioselective synthesis. Use of dimethyl dioxirane (DMDO) for the oxidation of enolsilanes has become a popular alternative to traditional conditions for Rubottom oxidations. This mild oxidant has been used to facilitate the isolation of 2-silyloxyoxiranes, which are stable under the essentially neutral reaction conditions." For example, treatment of 26 with DMDO at -40 °C afforded 27 in 99% yield.1 Ib These compounds can subsequently be converted to 2-hydroxyketones, as described above, or can be used in other transformations.12 Chiral dioxiranes generated in situ from chiral ketones and oxone have also been employed in enantioselective Rubottom oxidations developed independently by Shil3a and Adam.13b As shown above, enolsilane 28 was transformed to a-hydroxyketone 29 in 80% yield and 90% ee.l3a... 

Dimethyl dioxirane (DMDO) has also been employed as a mild and selective oxidant in Nef reactions.19 For example, treatment of nitroalkane 31 with KOf-Bu followed by DMDO provided enone 32 in 72% yield.20 The alkene isomerization that occurred in this case was desirable, as 32 represents the AB ring system of the natural product norzoanthamine. Many other oxidants have been used in Nef-type reactions,3,4 including alkali metal percarbonates or mixtures of K2CO3 and H2O2.21... 

In a similar manner, 2-thiouracils can be converted to numerous products when treated with ozone in the presence of dimethyl-dioxirane (DMDO or DDO). Again, a sulfinic acid intermediate is observed and the products of the reaction are dependent on the additives in the system. This methodology allows for the arrival at functionalized uracils in a manner akin to the reactivity pattern observed with pyrimidine-2-thiones (eq 58). ... 

The 1,2-anhydro-sugar (2), prepared by reaction of the corresponding glucal derivative with 3,3-dimethyl-dioxirane, has been used in the preparation of the -benayl- -D-glucosylamine (1) and the / -azide (3) (Scheme 1), A -(2-Hydroxyethyl)glycosylamines were formed in 73-... 

The oxidation of organic compounds by dioxiranes has attracted considerable interest in recent years. Bravo et al. have reported that the oxidation of a variety of organic compounds (alkanes, alcohols, ethers, aldehydes, and alkenes) by dimethyl-dioxirane may be explained via a radical mechanism. The proposed molecule-induced homolysis of dimethyldioxirane is supported by radical trapping with CBrCls or protonated quinolines. The presence of oxygen has also been shown to have a significant effect on these reactions and supports a radical mechanism. The... 

Epoxidation is an easy and extensively used method for creating reactive intermediates and is the focus of this section. The versatile reactivity of epoxy groups makes epoxidation of PBD a preferred first step for subsequent nucleophilic addition reactions. The epoxidation procedure used most frequently relies on percarboxylic acids, which are added as reagent or are prepared in situ. Epoxi-dations are also carried out with transition metal oxides as well as organic precursors such as dimethyl dioxirane. 

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