DMDO, Dimethyl dioxirane

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],... 

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>. 

Epoxidation of endocyclic enol ether 37 with dimethyl dioxirane (DMDO) followed by one-pot reduction with DIBALH produced a 10 1 mixtrrre of alcohols, in which the major isomer possessed... 

The highly potent antithrombotic (+)-rishirilide B was synthesized in the laboratory of S.J. Danishefsky. One of the tertiary alcohol functionalities was introduced via the Rubottom oxidation of a six-membered silyl dienol ether with dimethyl dioxirane (DMDO). The oxidation was completely stereoselective, and it was guided by the proximal secondary methyl group. Subsequently, the enone was converted to the enedione, which was used as a dienophile in the key intermoiecuiar Dieis-Aider cycioaddition step. 

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... 

Oxidation of cyclic enol ether 35 with dimethyl dioxirane (DMDO) followed by in situ reduction of the intermediate epoxide with DIBALH gave secondary alcohol as a 10 1 mixture of diastereom-ers. Oxidation of these alcohols with TPAP/NMO afforded a 10 1 mixture of ketone 37 and its C16 epimer. The isomers were separated and the minor isomer was recycled to a 4 1 mixture of isomers by treatment with imidazole. Subsequent construction of the D-ring was performed by radical reduction of mixed thioacetal in the same way as that adopted by the Sasaki group, leading to octacycle 38. Stereoselective installation of the triene side chain was then carried out via (Z)-vinyl iodide 39... 

An epoxidizing agent that has found widespread use is dimethyl dioxirane (DMDO). The reagent is generated from acetone and Oxone , a source of potassium peroxomonosulfate (KHSO5) (5.50). Epoxidation with DMDO occurs under mild, neutral conditions, without any nucleophilic component, which is ideal for preparing sensitive epoxides. For example, the enol ether 41 was epoxidized selectively using DMDO (5.51). ... 

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). ... 

SCHEME 2. Synthesis of dimethyl dioxirane (DMDO) and its use for epoxidation. 

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