Shi asymmetric epoxidation

An asymmetric epoxidation using fructose-derived chiral ketone. 

An asymmetric epoxidation using a fructose-derived chiral ketone. It is an organocatalyst with Oxone typically used as the primary oxidant. 

05 equiv ketone Cat 1.5 -2.1 equiv Oxone K2CO3, MeCN-DMM, . 55 Ph buffer, 0°C 

3 equiv ketone Cat 5.0 equiv Oxone NaHCOs, MeCN-aq. Na2EDTA 

substituted alkyl, substituted aryl, alkenyl, alkynyl 

There are two possible transition states spiro and planar. Nearly every example of frans-disubstituted and trisubstituted olefins which were studied with Shi s catalyst is consistent with the spiro transition state. The extent of the involvement of the competing planar transition state depends on the nature of the substituents on the olefins. 

The synthesis of cryptophycin 52 was accomplished by E.D. Moher et al. using the Shi epoxidation as the key step to install the epoxide moiety diastereoselectively. In the previous syntheses of this moiecuie, the epoxide moiety was always introduced in the last step, using common oxidants such as mCPBA or DMD, and with poor diastereoselectivity. Interestingly, the usual alkene precursor was a very poor substrate for the Shi epoxidation, so an earlier intermediate was subjected to the epoxidation conditions in which the pH was very carefully controlled. The desired epoxide was obtained as a 6.5 1 mixture of diastereomers. 

Four murisolin diastereoisomers which are demixed by using FluoroFlash silica gel followed by detagging 

The Shi epoxidation was the key step in E.J. Corey s total synthesis of the chiral C2-symmetric pentacyclic 

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Shi asymmetric epoxidation Chiral-ketone catalyzed epoxidation of unfunctionalized olefins. 410... 

Related reactions Davis oxaziridine oxidation, Prilezhaev reaction, Sharpless asymmetric epoxidation, Shi asymmetric epoxidation ... 

O. A. Wong, B. Wang, M. -X. Zhao, and Y. Shi, Asymmetric epoxidation catalyzed by a,a-dimethylmorpholinone ketone. Methyl group effect on spiro and planar transition states, J. Org. Chem., 74 (2009) 6335-6338. 

Oxone. DMD. Sharoless Epoxidation. Jacobsen-Katsuki Epoxidation. Corev-Chavkovskv reagent and Reaction. Shi (Asymmetric) Epoxidation. 

Shi Asymmetric epoxidation of alkenes catalyzed by chiral dioxanes... 

A group of polycyclic polyether natural products are of special interest owing to their fascinating structure and biological activities. One of the proposed biosynthetic origins of these molecules features an epoxide-opening cascade pathway. Shi asymmetric epoxidation of un-activated alkenes has been frequently employed in the preparation of polyepoxide intermediates. McDonald and co-workers studied a series of tandem e 7o-selective and stereospecific oxacyclization of polyepoxides mediated by Lewis acid. Polyepoxides, such as 64, can be obtained from the epoxidation of triene 63 with ketone 2. Furthermore, a cascade cyclization, initiated by a Lewis acid-promoted epoxide opening of 64, furnished the desired polyether 65. 

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