Norbomene oxidation

It appears that oxiranes known to give predominantly a-deprotonation in basic media (cyclopentene, cyclooctene and exo-norbomene oxide) are also the more strained (Table 1 entries 3, 6, 7). On the other hand, oxiranes that give mainly -deprotonation (butene, cyclohexene oxide) have lower strain energies and higher a-anion stabilities (Table 1 ... 

Bredt s rule and the blocked conformation (see Section n.A) precludes the ally lie alcohol formation, such as norbomene oxide jjowever, it has been very seldom... 

Norbomene oxide (equation 111) rearranges with apparent nonclassical ion involvement, to give a similar ratio of aldehyde (261) and norbomanone (262). ... 

Styrene oxide reacted rapidly but gave no volatile material, perhaps because of aldol polymerization of phenylacetaldehyde (the probable initial product). Norbomene oxide gave no detectable reaction, either because endo attack of bromide is especially unfavorable, or because the bromohydrin salt has no geometrically accessible alternative other than to return to epoxide. 

Reduction of epoxides. Hallsworth and Henbest (1,579,refs. 12 and 13)found that some steroidal epoxides, which were unreactive to lithium aluminum hydride, are easily reduced with a large excess of lithium in ethylamine. However, some olefin is also formed in some cases. Brown et al.1 now report that the combination of lithium and ethylenediamine at 50° is excellent for reduction of labile epoxides of bicyclic ketones, which are reduced only slowly by lithium aluminum hydride and usually with some extensive rearrangement. They chose ethylenediamine rather than ethylamine because the reduction is less vigorous in ethylenediamine than in ethylamine and thus easier to control. Also isolation of the alcohol is simplified because ethylenediamine is very soluble in water and only slightly soluble in ether, whereas ethylamine is miscible both in water and in ether. By this procedure, norbomene oxide (1) is reduced to pure ejco-norbomanol (2) in 87% yield (isolation). Analysis by glpc indicated that two rearranged alcohols (3, 4) are formed to a minor extent and that (2) is formed in 99.3% yield. 

Acrylonitrile or methyl acrylate readily inserts into allylnickel bonds (example 34, Table HI). A trans double bond is formed by loss of a proton. Insertion of acetylene followed by oxidative elimination with allyl halides gives cis double bonds (example 32, Table III). Insertion of methyl propiolate, followed by proton uptake, leads to a trans double bond (example 33, Table III). Norbomene has been shown to insert stereoselectively cis.exo into an allylnickel bond (example 35, Table III). 

Another convenient entry to fused cyclobutene-1,2-diesters was via site selective modification of the norbomene rt-bond in Smith s fe-alkene 49, e.g. treatment with 3,6-di(2 -pyridyl)-s-tetrazine 51 followed by DDQ oxidation afforded the cyclobutene-derivative 53 <97AA119>, while direct coupling with 3,5-f> (trifluoromethyl)-l,3,4-oxadiazo]e 54 furnished the tas(cyclobutene-l,2-diester) 55 (Scheme 6) <97SL196>. 

It was found that 2-propenyloxymagnesium bromide reacts much more readily with nitrile oxides than other known dipolarophiles of electron-deficient, electron-rich, and strained types, including 3-buten-2-one, ethyl vinyl ether, and norbomene, respectively (147). Therefore, this BrMg-alkoxide is highly effective in various nitrile oxide cycloaddition reactions, including those of nitrile oxide/Lewis acid complexes. 

The 1,3-dipolar cycloaddition reactions of nitrile oxides to unsymmetrically substituted norbomenes (243) and to dicyclopentadiene and its derivatives (244) proceed with complete stereoselectivity. The approach of the dipole takes place exclusively from the exo-face of the bicycloheptane moiety, generally... 

The results of the olefin oxidation catalyzed by 19, 57, and 59-62 are summarized in Tables VI-VIII. Table VI shows that linear terminal olefins are selectively oxidized to 2-ketones, whereas cyclic olefins (cyclohexene and norbomene) are selectively oxidized to epoxides. Cyclopentene shows exceptional behavior, it is oxidized exclusively to cyclopentanone without any production of epoxypentane. This exception would be brought about by the more restrained and planar pen-tene ring, compared with other larger cyclic nonplanar olefins in Table VI, but the exact reason is not yet known. Linear inner olefin, 2-octene, is oxidized to both 2- and 3-octanones. 2-Methyl-2-butene is oxidized to 3-methyl-2-butanone, while ethyl vinyl ether is oxidized to acetaldehyde and ethyl alcohol. These products were identified by NMR, but could not be quantitatively determined because of the existence of overlapping small peaks in the GC chart. The last reaction corresponds to oxidative hydrolysis of ethyl vinyl ether. Those olefins having bulky (a-methylstyrene, j8-methylstyrene, and allylbenzene) or electon-withdrawing substituents (1-bromo-l-propene, 1-chloro-l-pro-pene, fumalonitrile, acrylonitrile, and methylacrylate) are not oxidized. 

Insertion of aUcynes into aromatic C-H bonds has been achieved by iridium complexes. Shibata and coworkers found that the cationic complex [Ir(COD)2]BF4 catalyzes the hydroarylation of internal alkynes with aryl ketones in the presence of BINAP (24) [111]. The reaction selectively produces ort/to-substituted alkenated-aryl products. Styrene and norbomene were also found to undergo hydroarylation under similar condition. [Cp IrCl2]2 catalyzes aromatization of benzoic acid with two equivalents of internal alkyne to form naphthalene derivatives via decarboxylation in the presence of Ag2C03 as an oxidant (25) [112]. 

As stoich. [Ru(0)(bpy)(tmtacn)]VCH3CN it functioned as a competent (sic) epoxidant for alkenes, though the products were often contaminated with by-products (e.g. fran -stilbene gave fran -stilbene oxide and benzaldehyde cw-stilbene gave cis- and trans- epoxides). Kinetics of the epoxidation of norbomene and styrene were reported, with activation parameters measured and discussed [682]. Kinetics of its non-stereospecific, stoicheiometric epoxidation of aromatic alkenes in CH3CN were studied, and the rates compared with those of oxidations effected by other Ru(IV) 0x0 complexes with N-donors, e. g. [Ru(0)(tmeda)(tpy)] ", trans-[Ru(0)(Cl3bpy)(tpy)] " and [Ru(0)Cl(bpy)(ppz )] + [676]. 

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