Rearrangements, norbornene

The DMS method has not been employed yet for the generation of 117 and 123, since the dibromocarbene adducts of norbomadiene and norbornene rearrange under the usual conditions for the preparation [89]. However, they could be synthesized at -60 °C by taking advantage of tetrabromomethane and methyllithium as a source of the carbene [90] and could prove stable enough to serve as precursors of 117 and 123. On the other hand, the adducts of bromofluorocarbene to norborna-diene and norbornene having the fluorine atom in a cis-orientation should be isol-able at room temperature and hence be usable as stable precursors of 117 and 123. These variations ofthe DMS method were published on the occasion ofthe preparation of cycloadducts of l-oxa-2,3-cyclohexadiene (351) (Section 6.3.6) [35, 91], 1,2,4-cyclohexatriene (162) and 3d2-lJ-f-naphthalene (221) (Section 6.3.4) [35, 92],... 

The influence of the oxime geometry on the base-promoted rearrangement is pointed out for compounds 29 (85T5181). Thus, when treated with aqueous potassium hydroxide at room temperature, Z isomers 29Z (R = H, -oxyiminomethyl), arising as cycloadducts of the dimer or trimer of fulminic acid and norbornene, rearrange into 30. On the contrary, the E isomer 29E remains unchanged under similar conditions of aqueous bases (Scheme 6). 

Acetoxylchlorination of norbornene (138) proceeds with skeletal rearrangement in the presence of an excess of CuCl2 to give e.Yo-2-chloro-iyn-7-acetoxy-norbornane (139). This is a good synthetic method for ivn-7-norbornenol[163]. 

In an efficient diastereo-differentiative assembly of three components of norbornene, tv. v-alkenyl iodide, and KCN, the isomerization of the cis to the trans double bond takes place to give the coupled product 224. The isomerization is explained by the formation of the cyclopropane 222. its rearrangement to give a irans double bond in 223, and trapping with CN anion to give 224[168],... 

The carbonium ion rearrangements that can be observed in halofluonnations are illustrated by the reactions ot norbornene (Table 2) and norbornadiene (Table 3). Product ratios may vary with the different reagent combinations... 

Epoxidation of norbornene was found some time prior to this work not to stop at the monoepoxide step. Instead, this intermediate goes on to rearrange to the bicyclic aldehyde, 31, ... 

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 side products of the reaction between benzoylnitromethane 279 and dipolarophiles (norbornene, styrene, and phenylacetylene) in the presence of l,4-diazabicyclo[2.2.2]octane (DABCO) were identified as furazan derivatives (Scheme 72). The evidence reported indicates that benzoylnitromethane gives the dibenzoylfuroxan as a key intermediate, which is the dimerization product of the nitrile oxide. The furoxan then undergoes addition to the dipolarophile, hydrolysis, and ring rearrangement to the final products (furazans and benzoic acid) <2006EJ03016>. 

Treatment of the ketone (287) with pTsOH in benzene at 60 °C provided the norbornen-7-one derivative (288)98), following interesting acid-catalyzed rearrangement. 

In spite of the known tendency of norbornene and related systems to undergo rearrangements of the Wagner-Meerwein type during eleetro-philic addition, no such rearrangement was observed when norbornene underwent cycloaddition with the acridizinium or the. A/ -methylenium benzamide cation. As Schmidt correctly pointed out, this lack of rearrangement is an argument for a concerted reaction. Alternatively, if the cycloaddition is nonsynchronous, the time interval between step 1 and step 2 must be very short. 

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). ... 

Furazan formation by rearrangement of 2-isoxazoline oximes have also been reported <857727, 91KGS827>. For example, hydroxyiminoacetonitrile oxide reacts with norbornene to afford isox-azoline ( )- and (Z)-oximes (102) and (103) the former is stable in alkali whereas the latter rearranges to furazan (104) (Scheme 20) <85T518l>. 

Allenylidene-ruthenium complex Ib readily promotes the ROMP of norbornene, much faster than the precursor RuCl2(PCy3)(p-cymene) [39] (Table 8.1, entry 1). The ROMP of cyclooctene requires heating at 80 °C (5 min), however a pre-activation of the catalyst allows the polymerization to take place at room temperature. The activation consists, for example, in a preliminary heating at 80 °C or UV irradiation of the catalyst before addition of the cyclic aikene, conditions under which rearrangement into indenylidene and arene displacement take place [39] (Table 8.1, entries 2,3). The arene-free allenylidene complexes, the neutral RuCl2(=C=C=CPh2)... 

Similarly to aromatic n system, olefinic --electron donors also readily react with bissulfonyl peroxides. Norbornene, when reacted with bis(arylsulfonyl) peroxides, gives a disubstituted product following Wagner-Meerwein rearrangement (equation 6)42. 

The radical or ionic polymerization of norbornene yields a saturated polymer with a rearranged structure of 2,7 linkages (16). 

In some thermolysis reactions, amines (90 and 91) have been characterized.108,111,112,457 When R1 = CH2OH and R2 = H in Scheme 164, the aziridine undergoes spontaneous rearrangement (Scheme 166).125 An endo-triazoline adduct from norbornene yields a polymer as the principal... 

Acid-catalysed hydration of 2-norbornen-5-one (27) in aqueous HCIO4 results in the formation of hydroxyketone 28 and lactone 29 as the major products. Kinetic measurements suggest complex rearrangement pathways60. 

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