Dimethyldioxirane epoxidation with

Expedient removal of the volatiles after the epoxidation with dimethyldioxirane is crucial to achieve reproducible yields because the epoxide is extremely water sensitive. 

Epoxidation of allenes.1 The spirodioxides formed by epoxidation of allenes are unstable to acids, and only hindered ones have been obtained on epoxidation with peracids. They can be obtained, however, in 90-95% yield by epoxidation of allenes (even monosubstituted ones) with dimethyldioxirane in acetone buffered with solid K2C03. 

In the present work, the Jacobsen s catalyst was immobilized inside highly dealuminated zeolites X and Y, containing mesopores completely surrounded by micropores, and in Al-MCM-41 via ion exchange. Moreover, the complex was immobilized on modified silica MCM-41 via the metal center and through the salen ligand, respectively. cis-Ethyl cinnamate, (-)-a-pinene, styrene, and 1,2-dihydronaphtalene were used as test molecules for asymmetric epoxidation with NaOCl, m-CPBA (m-chloroperoxybenzoic acid), and dimethyldioxirane (DMD) generated in situ as the oxygen sources. 

TABLE 6. Classical reaction barriers (AE, kcal mol ) for ethylene epoxidation with peroxy-formic acid (PFA) and dimethyldioxirane (DMDO) at various levels of theory... 

Dimethyloxazolidines have been utilized as chiral auxiliaries for the diastere-oselective functionalization of the optically active tiglic acid derivatives by means of epoxidation with dimethyldioxirane (DMD) or m-CPBA and ene reactions with 02 or 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD). In the DMD and m-CPBA epoxidations, high diastereoselectivities but opposite senses of diastereomer selection was observed. In contrast, the stereochemistry of the 102 and PTAD ene reactions depended on the size of the attacking enophile whereas essentially perfect diastereoselectivity was obtained with PTAD, much lower stereoselection was observed with 02. The stereochemical results for the DMD and m-CPBA epoxidations and the PTAD ene reaction are explained in terms of the energy differences for the corresponding diastereomeric transition states, dictated by steric and electronic effects.200... 

The high proportion of axial attack on methylenecyclohexanes in epoxidation with peracids compared to peracid imides (see Section 4.5.1.1.3.) seems to indicate that the transition state of the peracid imide epoxidation is more crowded104-105 a similar, but somewhat less marked effect is observed in the epoxidation of 5-cholesten-3/ -ol (Table 3) with peracid imides and sterically demanding epoxidation reagents, such as (in situ generated) dimethyldioxirane (Table 3, entry 13 Table 4, entry 21), hydrogen peroxide/tungsten catalyst (Table 4, entry 16) or ferf-butyl hydroperoxide/molybdenum catalyst (Table 4, entries 14, 15). 

Upon epoxidation with peracids, alkylidenecycloproparenes react at the exocyclic double bond and are converted to hydroxy ketones 15. Epoxidation of l-(diphenylmethylene)cyclo-propa[6]naphthalene with dimethyldioxirane at — 18 "C afforded the epoxide, 3, 3 -diphenyl-spiro l//-cyclopropa[2ft]naphthalene-l,2 -oxirane (16), which was characterized by H and CNMR. This is the first oxaspiropentene ever characterized. Under non-acidic conditions rearrangement of the epoxide 16 to 2,2-diphenylcyclobuta[6]naphthalen-l(2//)-one (17) occurred in 86% overall yield. 

Although, as stated above, olefin epoxidation is commonly referred to as an electrophilic oxidation, recent theoretical calculations suggest that the electronic character of the oxygen transfer step needs to be considered to fully understand the mechanism [451]. The electronic character, that is, whether the oxidant acts as an electrophile or a nucleophile is studied by charge decomposition analysis (CDA) [452,453]. This analysis is a quantitative interpretation of the Dewar-Chatt-Dimcanson model and evaluates the relative importance of the orbital interactions between the olefin (donor) and the oxidant (acceptor) and vice versa [451]. For example, dimethyldioxirane (DMD) is described as a chameleon oxidant because in the oxidations of acrolein and acrylonitrile, it acts as a nucleophile [454]. In most cases though, epoxidation with peroxides occurs predominantly by electron donation from the 7t orbital of the olefin into the a orbital of the 0-0 bond in the transition state [455,456] (Fig. 1.10), so the oxidation is justifiably called an electrophilic process. 

The validity of the approach was first demonstrated by the synthesis of a linear tetrasaccharide [22] and a hexasaccharide 13 [23] as outlined in Scheme 3. Polymer-bound galactal 5 was converted to the 1,2-anhydro sugar 6 by epoxidation with 3,3-dimethyldioxirane [24], Polymer-bound 6 acted as a glycosyl donor when reacted with a solution of 7 in the presence of zinc chloride, resulting in the formation of disaccharide 8a. Upon repetition, this glycosylation procedure accommodated the secondary alcohol glycosyl acceptor 10 as well as disaccharide acceptor 12. Huor-idolysis with tetrabutylammonium fluoride (TBAF) was used to cleave the desired products from the polymeric support and furnish hexasaccharide 13 in 29% overall yield from 5 [16]. 

Conversion of 26 to the protected thioethyl glycosyl donors 27 was achieved through epoxidation with dimethyldioxirane to yield the 1,2-anhydro sugar, followed... 

Experimental. Opening of glycal epoxide with ethylthiol [63] A suspension of polymer-bound glycal 35 (1.0 g) in dichloromethane (20 mL) was treated with dimethyldioxirane as described previously to give epoxide 36. This resin was suspended in a mixture of dichloromethane (10 mL) and ethanethiol (10 mL), cooled to —78°C, and treated with trifluoroacetic an-... 

Dimethyldioxirane, together with acetone, is removed from the reaction vessel by distillation. The yellow 0.1-0.2 M solution can be used as an oxidizing agent, e.g. for the epoxidation of olefins [19], for the oxidation of enolates to a-hydroxycarbonyl compounds and for the oxidation of primary amines into nitro compounds ... 

Chiral Auxiliary-hased Epoxidation of Substituted Alkenes. High diastereoselectivities were found for the m-CPBA or dimethyldioxirane epoxidation of chiral oxazolidine-substituted alkenes bearing a strongly basic urea group (eq 29). However, in most cases, the diastereoselectivities were superior with dimethyldioxirane. 

An in situ method for epoxidations with dimethyldioxirane using buffered aqueous acetone solutions of Oxone has been widely applied.The epoxidation of 1-dodecene is particularly impressive in view of the difficulty generally encountered in the epoxidation of relatively unreactive terminal alkenes (eq 7). A biphasic procedure using benzene as a cosolvent and a phase-transfer... 

The first total synthesis of staurosporine and of e/it-staurosporine has been reported in full (see Vol. 29, p. 378). The glycal-derived epoxide 191 (from dimethyldioxirane epoxidation of the precursor glycal) was treated with the sodium salt of 190 and the product, 192, was then elaborated using iodoamina-tion as the the key cyclization step, radical deiodination then affording 193, an intermediate for synthesis of e r-staurosporine. ... 

The stereochemical outcome of the epoxidation can be rationalized by a spiro transition state model. Two extreme epoxidation modes, spiro and planar, are known for epoxidation with dimethyldioxirane, and the spiro transition state is the optimal transition state for oxygen atom transfer from... 

Glycal related dienes like 19, prepared by base treatment of the corresponding 6-<9-mesyl glycals have been described as substrates for epoxidation with dimethyldioxirane, mid are usefiil precursors for making the protein kinase C inhibitor, staurosporine. ... 

Spiro transition state is proposed to be the major transition state for the epoxidation with dimethyldioxirane based on the observation that ds-hexene is epoxidized 7-9 times fester than trans-hexene (a) Baumstark, A.L and McCloskey, C.J. 

Fullerene epoxide, C )0, is formed by the UV irradiation of an oxygenated benzene solution of Cfio The O atom bridges a 6 6 bond of the closed fullerene structure. The same compound is also formed as one of the products of the reaction of Cgo with dimethyldioxirane, Mc2COO (see later). ... 

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