Olefinic compounds, rearrangements

Olefinic compounds such as a-pinene (309) and /Dpi none (312) undergo hydrogen abstraction followed by rearrangement and amino-oxyl insertion (310, 313) and addition reactions (311, 314, 315), as shown in reactions 43 and 44627. Other olefinic compounds such as norbomadiene, cyclo-octene and cyclo-octa-1,5-diene gave analogous results628. 

Reviews have featured epoxidation, cyclopropanation, aziridination, olefination, and rearrangement reactions of asymmetric ylides 66 non-phosphorus stabilized carbanions in alkene synthesis 67 phosphorus ylides and related compounds 68 the Wittig reaction 69,70 and [2,3]-Wittig rearrangement of a-phosphonylated sulfonium and ammonium ylides.71 Reactions of carbanions with electrophilic reagents, including alkylation and Wittig-Homer olefination reactions, have been discussed with reference to Hammett per correlations.72... 

Migrations of the double bond and carbon-skeleton rearrangements are important in the preparation of several olefinic compounds. A number of alkyl cyclopentenes are available in quantities suitable for synthetic work by the isomerization of cyclohexene and its homologs over alumina at 470- 480°. o-Allylphenol is isomerized by methanolic potassium hydroxide at 110° to o-propenylphenol (75%). Several /5, y-olefinic acids are conveniently obtained from the corresponding a /3-isomers by equilibration in basic media. The two isomeric acids are readily separated by partial esterification of the resulting mixtures since the /3,y-isomers are more easily esterified. "... 

Snatzke [102] has shown that the 3,5,6-triacetate (10), though resistent to mild reaction conditions, can be forced to react via a C<5>-carbonium ion species by heating in acetic anhydride containing an acidic catalyst. A major product, apart from Westphalen s diacetate , was another olefinic compound identified by Blunt, Hartshorn and Kirk [103] as the A 2h7) olefin (ii) resulting from a backbone rearrangement of the steroid skeleton cf. p. 292). 

A recent attempt to repeat the rearrangement of the 3a-acetoxy 5a, 6a-epoxide (so) to obtain the 5)S-6-ketone gave instead a mixture of six products, with the 6-ketone only as a minor constituent [6a]. The major products were the and A8(i4).olefinic compounds... 

Aggarwal VK, Winn CL. Catalytic, asymmetric sulfur ylide-mediated epoxidation of carbonyl compounds scope, selectivity, and applications in synthesis. Acc. Chem. Res. 2004 37 611-620. Li A-H, Dai L-X, Aggarwal VK. Asymmetric ylide reactions epoxidation, cyclopropanation, aziridination, olefination, and rearrangement. Chem. Rev. 1997 97 2341-2372. 

A retro-Westphalen rearrangement occurred when the 10) -fluoro-5) -methyl-7j -ol (396) was treated with boron trifluoride, to abstract fluoride ion. The product was the 4-en-7)3-ol (397). Contrasting behaviour when a 10)8-hydroxy-group was eliminated by acid treatment, reported last year to give a backbone-rearranged A -olefinic compound, requires an explanation. The most obvious difference in the reactants, apart from the different 10)8-leaving... 

A re-investigation " of the decomposition of the 12-tosylhydrazone (529) of hecogenin acetate by bases shows that aprotic media lead to formation of the 11-ene (530), probably via a carbene intermediate. Hydroxylic solvents protonate the intermediate diazo-compound, leading to the olefinic product (531) by rearrangement of a C-12 carbonium ion. The related solvolysis of the 12/9-tosylate (532) gives the stable 13(17a)-olefinic compound (531) at high temperatures, and... 

The utility of the Chugaev elimination for the formation of olefins without rearrangement of the carbon skeleton can be observed upon pyrolysis of the xanthate of alcohol 14.17 The desired vinyl cyclopropane (IS) was isolated in reasonable yield (42%) along with a small amount of the rearranged xanthate. Alternatively, acid-mediated dehydration with sulphuric acid yielded a variety of rearranged products in low yield. Ester pyrolysis (of the acetate of 14) also furnished a variety of compounds, with the major product being cyclopentene 16. 

Butadiene and other olefinic compounds polymerize in anhydrous liquid hydrogen fluoride or undergo rearrangement reactions. While aliphatic saturated hydrocarbons are usually insoluble, aromatic hydrocarbons are soluble and capable of accepting a proton23-25 Acetic acid and even trifluoroacetic acid act as proton acceptors in liquid hydrogen fluoride ... 

Sen, A. Lai, T. W. Thomas, R. R. Reactions of electrophilic transition metal cations with olefins and small ring compounds. Rearrangements and polymerizations. J. Organomet. Chem. 1988, 358, 567-588. 

The coordinatively unsaturated cobalt hydrotricarbonyl which is formed via (1 a) reacts with the olefinic compound with formation of a 7r-com-plex (lb), the 7r-complex is rearranged with formation of a cobalt-carbon... 

Later examples of the olefination of carbonyl compounds, which are extremely sensitive towards acid or basc catalyzed rearrangements, have been given by G. Buchi and by R.B. Woodward. 

Nickel(O) forms a n-complex with three butadiene molecules at low temperature. This complex rearranges spontaneously at 0 °C to afford a bisallylic system, from which a large number of interesting olefins can be obtained. The scheme given below and the example of the synthesis of the odorous compound muscone (R. Baker, 1972, 1974 A.P. Kozikowski, 1976) indicate the variability of such rearrangements (P. Heimbach, 1970). Nowadays many rather complicated cycloolefins are synthesized on a large scale by such reactions and should be kept in mind as possible starting materials, e.g. after ozonolysis. 

Thallium(III) acetate reacts with alkenes to give 1,2-diol derivatives (see p. 128) while thallium(III) nitrate leads mostly to rearranged carbonyl compounds via organothallium compounds (E.C. Taylor, 1970, 1976 R.J. Ouelette, 1973 W. Rotermund, 1975 R. Criegee, 1979). Very useful reactions in complex syntheses have been those with olefins and ketones (see p. 136) containing conjugated aromatic substituents, e.g. porphyrins (G. W. Kenner, 1973 K.M. Smith, 1975). 

Sulfonamides. A/-Halo-A/-alkylsulfonamides, RS02NR X, are relatively stable distillable Hquids. Under the influence of uvlight they form 1 1 adducts with olefins (67,100). Ai-/-Butyl derivatives rearrange forming precursors to cyclopropanes and sultams. A/-Halo-A/-sodioalk5lsulfonamidates, RS02NClNa, have been less extensively studied than their aromatic counterparts (70). The stabiHty of these compounds approaches that of the aromatic sulfonamides (80). The dodecyl compound exhibits properties of both a disinfectant and a surfactant. 

The Bamford-Stevens decomposition of tosylhydrazones by base has been applied to steroids, although not extensively. It has been demonstrated that the reaction proceeds via a diazo compound which undergoes rapid decomposition. The course of this decomposition depends upon the conditions in proton-donating solvents the reaction has the characteristics of a process involving carbonium ions, and olefins are formed, often accompanied by Wagner-Meerwein-type rearrangement. In aprotic solvents the diazo compound appears to give carbene intermediates which form olefins and insertion products ... 

The carbocation may rearrange, eliminate a proton to produce an olefin, or crack at a beta position to yield an olefin and a new carbocation. Under an atmosphere of hydrogen and in the presence of a catalyst with hydrogenation-dehydrogenation activity, the olefins are hydrogenated to paraffinic compounds. This reaction sequence could be represented as follows ... 

Simple diastereoselection in the reactions of 2-butenylboron compounds and aldehydes is critically dependent on the configurational stability of the reagentslb. As a general rule, most 2-bulenylorganometallics arc sensitive to sequential 1,3-metal shifts (1,3-metallotropic rearrangements) that result in E- to Z-olefin isomerization via the l-methyl-2-propenylmetal isomer. 

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