Asymmetric Peterson reaction

C-Silylation of Li-Ester Enolates. Further applications of a-diphenylmethylsilyl carhoxylates have been reported. Gais and co-workers employed a-methyldiphenylsilyl acetate (16), prepared from (—)-8-phenylmenthol acetate (15), by lithiation with LDA and reaction with methyldiphenylchlorosilane, in an asymmetric Peterson reaction with the bicyclo[3.3.0]octan-3-one derivative (17) to yield a 89 11 mixture of the (Z)- and ( )-esters (18) and (19) About 50% of the starting material was recovered in the unoptimized procedure (eq 13). ... 

Asymmetric Peterson reaction of symmetrically substituted cyclohexanone derivatives with the lithium enolate of silanylacetate 219 in the presence of chiral... 

Chiral tridendate ligands have been utilized to effect asymmetric Peterson reactions, resulting in olefins with axial chirality in high yields and enantioselectivities. This is reported as the first example of its kind, namely the enantioselective Peterson olefmation of a-silanyl ester enolates 33 with substituted cyclohexanones 32, facilitated by an external chiral ligand 34. 

The cyclohexyloxy(dimethyl)silyl unit in 8 serves as a hydroxy surrogate and is converted into an alcohol via the Tamao oxidation after the allylboration reaction. The allylsilane products of asymmetric allylboration reactions of the dimethylphenylsilyl reagent 7 are readily converted into optically active 2-butene-l, 4-diols via epoxidation with dimethyl dioxirane followed by acid-catalyzed Peterson elimination of the intermediate epoxysilane. Although several chiral (Z)-y-alkoxyallylboron reagents were described in Section 1.3.3.3.3.1.4., relatively few applications in double asymmetric reactions with chiral aldehydes have been reported. One notable example involves the matched double asymmetric reaction of the diisopinocampheyl [(Z)-methoxy-2-propenyl]boron reagent with a chiral x/ -dialkoxyaldehyde87. 

This reaction has been modified by the use of an a-silyl selenoacetamide to generate -olefins in preference and the use of an a-silyl thioether and A-cyclohexyl-(2-triethylsilylpropylidene)imine as of-silyl carbanion precursors. In addition, a germanium-Peterson reaction" and a tin-Peterson reaction" have been developed. Furthermore, an asymmetric version of the Peterson olefination has been developed by the use of an external chiral tridentate amino diether as a chiral ligand. ... 

Floreancig completed the total synthesis of (+)-dactylohde via a sequential Peterson olefination and an intramolecular Hosomi-Sakurai-Prins cycli-zation of the acetal-linked substrate (Scheme 32). Macrocychzation was performed by Horner-Emmons olefination as Smith did (Sect. 3.2.1). The key element of 2,6-cfs-tetrahydropyran in 155 was constructed via the sequential cyclization starting from acetal 156, which involved aldehyde 157 and 1,3-diol 158, synthesized via Denmark s asymmetric aldol reaction and Stille coupling. 

Chiral secondary allylic alcohols 202 are synthesized from allylsilanes and vinylsilanes by way of successive asymmetric dihydroxylation (AD) and Peterson elimination although the Peterson reaction process does not constitute asymmetric induction, it results in the loss of an asymmetric point (Scheme 2.128) [357]. The allylsilane undergoes efficient dihydroxylation using AD-mtx-a, AD-mtx-, or the modified Sharpless AD reagents, although enantiomeric excess is dependent on the stmcture of the alkene [358, 359]. 

Gais, H.-J., Schmiedl, G., and Ossenkamp, R.K.L., Total synthesis of (-i-)-3-oxacarbocyclin. Part 1. Retrosynthesis and asymmetric olefination through Horner-Wadsworth-Emmons, Peterson and Martin reactions, Liebigs Ann., 2419, 1997. 

Stereoselectivity. See Asymmetric induction Axial/equatorial-, Cis/trans-, Enantio-, Endo/exo- or Erythro/threo-Selectivity Inversion Retention definition (e.e.), 107 footnote Steric hindrance, overcoming of in acylations, 145 in aldol type reactions, 55-56 in corrin synthesis, 261-262 in Diels-Alder cyclizations, 86 in Michael type additions, 90 in oiefinations Barton olefination, 34-35 McMurry olefination, 41 Peterson olefination, 33 in syntheses of ce-hydrdoxy ketones, 52 Steric strain, due to bridges (Bredt s rule) effect on enolization, 276, 277, 296, 299 effect on f3-lactam stability, 311-315 —, due to crowding, release of in chlorophyll synthesis, 258-259 in metc-cyclophane rearrangement, 38, 338 in dodecahedrane synthesis, 336-337 in prismane synthesis, 330 in tetrahedrane synthesis, 330 —, due to small angles, release of, 79-80, 330-333, 337... 

The synthesis of seven-membered rings from furans and a,a -dibromoketones via oxyallyl intermediates is well known. It was reported that this reaction occurs quite easily when water is used as solvent <97TL8031>. In a study on the influence of steric and electronic effects on a function attached at C-2 of furans in the yield and diastereoselectivity of [4 + 3] cycloaddition reactions with oxyallyl cations it was found that in almost all cases a c/x-diastereospecificity and a high endo diastereoselectivity is obtained <97T11669>. A tandem Peterson olefination-[4 + 3] cycloaddition reaction with furans has been reported <97JOC1578 97TL386l>. For an intramolecular [4 -t- 3] cycloaddition see <97JOC6051>. The first asymmetric [4 + 3]... 

Predict the products expected from the following hydroboration-oxidation reactions. (Prostaglandins-23) (Masamune, S. Kim, B. Peterson, J. S. Sato, T. Veenstra, S. J. Organoboron compounds in organic synthesis. 1. Asymmetric hydroboration /. Am. Chem. Soc. 1985, 107, 4549 951). 

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