M-CPBA epoxidation

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... 

Next, the double bond is made into an epoxide with m-CPBA. Epoxides react with nucleophiles, and this is the way that the four-membered ring of grandisol was formed the nitrile still has a proton next to it, and a strong base will remove this proton as before to give an enolate . The enolate reacts with the epoxide to give a four-membered ring. 

It is all true. Evidence that a silyl group stabilizes the S 2 transition state comes from the reactions of the epoxides of vinyl silanes. These compounds can be made stereospecifically with one equivalent of a buffered peroxy-acid such as m-CPBA. Epoxidation is as easy as the epoxidation of simple alkenes. You will see in a moment why acid must be avoided. 

The alkylation subunit of CC-1065 and duocarmycin has been efficiently synthesized using [Mn(salen)]-catalyzed epoxidation [85]. AE of intermediate 30 using low-temperature m-CPBA epoxidation conditions [77] afforded the epoxide 31 in 70% yield and 92% ee (Scheme 12). Reductive cleavage of the epoxide... 

Perbenzoic acid was one of the first peracids used to epoxidize PBD [118, 131]. Internal double bonds are epoxidized quantitatively by perbenzoic acid in the presence of the double bonds of 1,2-inserted butadienes [132]. This one-phase reaction can be used analytically to determine the content of 1,4-inserted units in PBD [131]. The commercial availability of m-CPBA makes it the preferred peroxide for epoxidation [100, 133-139]. m-CPBA epoxidizes double bonds quantitatively, although the 1,4-inserted butadiene units react faster [100]. The final epoxide content of the PBD can, thus, be controlled by the amount of m-CPBA added [138]. Despite its chemical benefits, m-CPBA is not used in large-scale epoxidation because of its high cost and the cost of disposal of mefa-chlorobenzoic acid residue. Epoxidations of PBDs are described with monoperphthalic acid using reactive mixing techniques [140]. The preparation of perphthalic acid from phthalic acid anhydride and hydrogen peroxide in solution was found to be convenient for the preparation of epoxidized polyenes, without notable side reactions [107, 141-143]. 

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