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. 

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. 

Cyclic 1,2-diamines are cleaved to diketones with dimethyl dioxirane. a-Diketones and a-hydroxy ketones are also cleaved by alkaline H202. HIO4 has... 

All classes of primary amine (including primary, secondary, and tertiary alkyl as well as aryl) are oxidized to nitro compounds in high yields with dimethyl dioxirane." Other reagents that oxidize various types of primary amines to nitro compounds are dry ozone, various peroxyacids," MeRe03/H202,"" Oxone ," ° tcrt-butyl hydroperoxide in the presence of certain molybdenum and vanadium compounds, and sodium perborate." ... 

Dimethyl dioxirane in wet acetone oxidizes isocyanates to nitro compounds (RNCO —> RN02). Oximes can be oxidized to nitro compounds with peroxytri-fluoroacetic acid, or Oxone ," sodiumperborate," among other ways. " Primary and secondary alkyl azides have been converted to nitro compounds by treatment with PhjP followed by ozone. Aromatic nitroso compounds are easily oxidized to nitro compounds by many oxidizing agents. ... 

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],... 

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) . 

In recent years, dioxiranes have become workhorses for a variety of selective transformations in organic synthesis, from epoxidation of alkenes to the conversion of alcohols into fee corresponding ketones <99CJC308>. Dioxirane-mediated epoxidation continues to be the method of choice for complex substrates wife acid-sensitive functionality. Thus, fee dimethyl-dioxirane (DMD)-mediated epoxidation of the silylated stilbene lactam 159 has been reported as a key step in fee synthesis of protoberberines <99JOC877>. 

In related work from the same group, dehydro-nucleoside 21 underwent stereospecific epoxidation with dimethyl-dioxirane (DMDO) to give epoxide 22. The ring opening of this compound with trimethylaluminium is presumably a predominantly S m1 process giving isomers 23 and 24 in a 5 1 ratio (Scheme 4) <2004JOC1831>. 

Zur Oxidation von Amino-furazanen zu Nitro-furazanen mit Dimethyl-dioxiran s. Lit.262. 

Dimethyl-dioxiran oxidiert prim. Amine auf einfache und milde Weise in hohen Ausbeuten zu Nitro-Verbindungen. So laflt sich Butyl-amin zu 1-Nitro-butan oxidieren (84%)2. 

A recent report (J. Org. Chem. 2004, 69, 8510) by Paul G. Williard of Brown University and Ruggero Curci of University di Bara of the oxidation of 5 to 6 serves as a timely reminder that the widely-used epoxidation reagent dimethyl dioxirane is also useful for the oxidation of secondary alcohols to ketones. 

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. 

Steric effects were responsible for the complete diastereocontrol observed in the oxidation of various 6-halopenicillins by dimethyl dioxirane (DMD). Only one of the two possible diastereomeric sulfoxides has been obtained in each case23 (Table 1). Scheme 3 shows that perborate oxidation of optically active sulfide 16 affords, with moderate diastereoselectivity (78% de), the (f )-sulfoxide 17,24 designed as chiral ligand for catalytic asymmetric synthesis. 

Dimethyl dioxirane (DMD) also performs epoxidation of enamines. Since the epoxide intermediate is unstable, it dimerizes to give 1,4-dioxane derivatives57. It can, however, be trapped by methanol at — 70 °C (Scheme 39). 

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