Norbornene oxidation

Whereas exo-norbornene oxide rearranges to nortricyclanol on treatment with strong base through transannular C-H insertion (Scheme 5.11), endo-norbornene oxide 64 gives norcamphor 65 as the major product (Scheme 5.14) [15, 22]. This product arises from 1,2-hydrogen migration very little transannular rearrangement is observed. These two reaction pathways are often found to be in competition with one another, and subtle differences in substrate structure, and even in the base employed, can have a profound influence on product distribution. 

The problem of diastereoselectivity in additions to cyclic radicals arising from the opening of bi- or tricyclic epoxides, e. g. cycloheptene oxide or norbornene oxide, has been addressed only recently [32], In the former case, reasonable selectivities can be obtained with titanocene dichloride (trans cis = 76 24), but excellent selectivities are observed with bis(tert-butyl)titanocene dichloride (transxis = 94 6), as shown in Scheme 12.17. 

The desymmetrization works also well with higher substituted meio-epoxides such as ewdo-norbornene oxide (130) , cis-5,6- and 4,7-difunctionalized cyclooctene oxides 132 and 134, giving the alcohols 131, 133 and 135, respectively but for the diastereomer 136, the rearrangement to form the allylic alcohol 138 beside 137 cannot be completely suppressed (equation 29 best results are given). ... 

As seen above, /3-deprotonation implies a six-center transition state. Recent computational studies show an important variation of the H —C—C—O dihedral angle from reactant to transition state . Thus, the ground state geometry of the oxirane cannot be used to predict its reactivity. However, for structural reasons, some oxiranes cannot adopt a suitable conformation for -deprotonation and furnish exclusively a-deprotonation products. This concept is well illustrated by the norbornene oxide 17, which gives exclusively the transannular 1,3 insertion product 18 in the presence of lithium amide (Scheme 5) . 

The classical isomerization of jco-norbornene oxide 82 to nortricyclanol 83 <1964JOC2830> was next examined (Scheme 38) chiral lithium amides or organolithium/(—(-sparteine complexes effected this transformation, with up to 52% ee <1996TA1275>. 

In contrast to the PhlO/Mn(TPP)Cl system, epoxidation of alkenes occurs with high retention of configuration. cis-Alkenes are almost exclusively converted to cis-epoxides. Norbornene is transformed into a 67 3 mixture of exo- and e do-norbornene oxide e.g. equation 223)." ... 

Key Words Ethylene oxide, Propylene oxide. Epoxybutene, Market, Isoamylene oxide. Cyclohexene oxide. Styrene oxide, Norbornene oxide. Epichlorohydrin, Epoxy resins, Carbamazepine, Terpenes, Limonene, a-Pinene, Fatty acid epoxides, Allyl epoxides, Sharpless epoxidation. Turnover frequency, Space time yield. Hydrogen peroxide, Polyoxometallates, Phase-transfer reagents, Methyltrioxorhenium (MTO), Fluorinated acetone, Alkylmetaborate esters. Alumina, Iminium salts, Porphyrins, Jacobsen-Katsuki oxidation, Salen, Peroxoacetic acid, P450 BM-3, Escherichia coli, lodosylbenzene, Oxometallacycle, DFT, Lewis acid mechanism, Metalladioxolane, Mimoun complex, Sheldon complex, Michaelis-Menten, Schiff bases. Redox mechanism. Oxygen-rebound mechanism, Spiro structure. 2008 Elsevier B.V. 

Norbornene oxide can react with a Z zs-(cyclopentadienyl)(ferf-butylimido)-zirconium complex (Cp2Zr=N-f-Bu) tetrahydrofuran (THF) to produce the... 

D. M. Hodgson, R. Wisedale, Enantioselective rearrangement of exo-norbornene oxide to nortricyclanol, Tetrahedron Asymm. 7 (1996) 1275. 

The results of recent investigations S of model systems provide compelling evidence that stabilized atomic oxygen is present in Compound I and Compound II of horseradish peroxidase. Thus, the combination of tetrakis(2,6-dichlorophenyl)-porphinato-iron(ni) perchlorate (6, Scheme 4-4) with pentafluoro-iodosobenzene, zn-chloroperbenzoic add, or ozone in acetonitrile at -35°C yields a green porphyrin-oxene adduct (7). This species, which has been characterized by spectroscopic, magnetic, and electrochemical methods, cleanly and stereospecifically epoxidizes olefins (>99% exo-norbornene-oxide). 

A more recent example of chiral lithium amide-induced enantioselective deprotonation-rearrangement is the conversion of exo-norbornene oxide to nor-tricyclanol which proceeds via the Hthiated epoxide 43 (Scheme 22) [82]. 

In the above case no P-elimination can occur. Reversibility observed during the a-deprotonation of such an epoxide with a lithium amide (vide supra) might result in lowering the ee when using a chiral lithium amide, since reversible deprotonation could compromise the kinetic control in enantioselective deprotonation. Nevertheless deprotonation of exo-norbornene oxide 91 with lithiiun (S,S)-bis(l-phenyl)ethylamide 11 [Eq. (7)] gave tricyclanol 92 in good yield (73%) and moderate ee (49%) (Scheme 16). When the rearrangement of exo-norbornene oxide 91 is carried out with s-BuLi in pentane from -78°C to room... 

The solution structure of 4 and its conversion to the norbornene oxide has been studied [127,128]. Selective epoxidation via pure 0 atom transfer occurs in aprotlc solvents in the absence of nucleophiles. The latter would cleave the Pd-C bond to afford chlorohydroxy- and chloronitronorbornanes. 

In the presence of equimolar norbornene after the same irradiation, the much larger amount of recovered diketone was only 8% exchanged, while there was a 90% conversion to norbornene oxide whose oxygen was 93% 0. 

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