Sharpless epoxidation rearrangement

Sesquiterpenoid. 203, 1071 Sex hormone, 1082-1083 Sharpless, K. Barry. 734 Sharpless epoxidation, 735 Shell (electron), 5 capacity of, 5 Shielding (NMR). 442 Si prochirality, 315-316 Sialic acid. 997 Side chain (amino acid), 1020 Sigma (cr) bond, 11 symmetry of, 11 Sigmatropic rearrangement, 1191-1195... 

Diepoxidation of a diene Diepoxidation of the diene 1 with m-chloroper-benzoic acid gives a mixture of the d,l- and meso-diepoxides, whereas Sharpless epoxidation results in d- or 1-2 by a double asymmetric epoxidation. On treatment with base, 2 rearranges to the diepoxide a and then cyclizes to the meso-tetra-hydrofuran 3, a unit of teurilene, a cytotoxic C, -cyclic ether of red algae. This... 

Payne rearrangement. The Payne rearrangement2 of a primary cts-2,3-epoxy alcohol to a secondary 1,2-epoxy alcohol usually requires a basic aqueous medium, but it can be effected with BuLi in THF, particularly when catalyzed by lithium salts. As a consequence, the rearrangement becomes a useful extension of the Sharpless epoxidation, with both epoxides available for nucleophilic substitutions. Thus the more reactive rearranged epoxide can be trapped in situ by various organometallic nucleophiles. Cuprates of the type RCu(CN)Li are particularly effective for this purpose, and provide syn-diols (3).3... 

Isomerization of primary allylic alcohols proceeds in dichloromethane at 25 °C in the presence of a catalyst prepared in situ from VO(acac)2 or Mo02(acac)2 and BTSP to give tertiary isomers in good yields. This is in sharp contrast to the well-known Sharpless epoxidation of allylic alcohols. The catalysts are also effective for rearrangements of secondary-tertiary allylic alcohols. The isomerization of an allenyl allylic... 

The (panial) description of the synthesis and coupling of the live fragments starts with the cyclohexyl moiety C21—CM The first step involved the enantio- and diastereoselective Sharpless epoxidation of l,4-pentadien-3-ol described on p 126f The epoxide was converted m four steps to a 3-vinyl 6-lactone which gave a 3-cydohexenecarboxylate via Ireland-Claisen rearrangement (cf p 87) Uncatalysed hydroboration and oxidation (cf. p 131) yielded the desired muis-2-methoxycydohexanol which was protected as a silyl ether The methyl car-... 

While the known desymmetrization of divinylcarbinol by asymmetric Sharpless epoxidation worked well, introduction of the PMB group (which was chosen for its mild removal conditions) required the use of the unstable, non-commercially available PMB bromide (using the commercially available but less reactive PMB chloride, in presence of NaH, led to Payne rearrangement). 

A considerable amount of work was required to optimize the leaving group and avoid racem-ization through a Payne rearrangement mechanism.12 Of course, the Sharpless epoxidation of allyl alcohols is well-known to access these 3-functionalized epoxides. 

Introduction Catalytic methods of asymmetric induction Part I - Sharpless Asymmetric Epoxidation The AE Method The ligands The catalyst Catalyst structure The mnemonic device The synthesis of propranolol Modification after Sharpless Epoxidation Oxidation after Sharpless epoxidation The Payne rearrangement... 

The products of a Sharpless epoxidation, such as epoxides 12, 16, or 22, are potentially unstable in base as the anion of the alcohol can attack the epoxide 24 in the Payne rearrangement. This is easily seen with the simplest compound 12. It doesn t and we have rather given the game away by the compound numbers. The OH groups in the right hand and in the left hand compounds 12 are homotopic. Sharpless made the definitive statement of this in his propranolol synthesis.6... 

The homochiral acetylenic alcohol 2 [derived from ( )-4-benzyloxy-2-butenol by asymmetric Sharpless epoxidation via 2 in four steps] is transformed either to ( )-3 by treatment w ith lithium aluminum hydride or to (Z)-4 by hydrogenation with Lindlar catalyst. Simple Claisen or ortho ester rearrangement yield the same, but enantiomeric, products 5 and 6 with 85-90% ee288. 

P-Siloxyaldehydes. Chiral epoxy alcohols are readily available (e.g., by Sharpless epoxidation of allylic alcohols). Their transformation via a stereoselective rearrangement-silylation induced by the silyl triflate and i-Pr2NEt opens a new way to protected aldols. 

The Payne rearrangement of epoxy-alcohols is a special case of an intramolecular nucleophilic opening of epoxides and is of synthetic significance due to its application to Sharpless epoxides. ... 

The encouraging result of the trans-epoxy acylates with the chiral spiro compounds was appUed to the optically active system (Scheme 15). Asymmetric reduction of the enone 31 by Corey s method [72] afforded the allyl alcohol (-)-34 (90% ee). Epoxidation of (-)-34 by the stereoselective Sharpless epoxidation [73] afforded the cts-epoxy alcohol, cfs-(-)-35, as the sole product. The Mitsunobu reaction [74] of czs-(-)-35 with benzoic acid gave the trans-epoxy benzoate, trans- -)-36, (90% ee) in 89% yield. Treatment of trans-(-)-36 with BF3-Et20 afforded the optically active spiro compound (+)-37 in 89% yield with retention of the optical purity (90% ee). This means that the rearrangement occurs stereospecifically. The optically pure epoxy camphanate (-)-38 could be obtained after one recrystallization of the crude (-)-38 (90% de), which was obtained by the Mitsimobu reaction of cfs-(-)-35 with D-camphanic acid. The optically pure spiro compoimd (+)-39 (100% de) was obtained from the optically pure (-)-38 in 89% yield. 

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