Norbomene rearrangement

After elimination of ethoxytrimethylsilane, 7,7-dimethyl-1-norbomene (6) rearranges to 3,3-dimethyl-2-norbomylidene (7), which undergoes a 1,3-CH insertion reaction into the endo-6-H to give tricyclane 8. Nortricyclane formation has been shown to be the fastest intramolecular mode of stabilization of 2-norbomylidene.5,6... 

At a barrier of 42.5 kcal/mol, the least probable rearrangement will be the reaction of 1-norbomene 16 going to carbene 31. The rearrangement of 30 to 32 needs 26.8 kcal of activation. At an energy difference of only 4.2 kcal/mol between 30 and 32, an interconversion under strongly forcing reaction conditions might be possible. This also holds for the conversion of 16 -> 32,... 

However, a better known version of the 2-aza-Cope rearrangement is that carried out by using 2-aza-l,5-hexadienes 619 (equation 269) and particularly their iminium ion counterparts, usually N-acyliminium cations 620 (equation 270)365,366 (for reviews, see also Reference 367). Aza-Cope rearrangement of the norbomene ester 621 leads to tetrahydropyridine ester 622 when allowed to stand in solution at room temperature for... 

The stereospecific anti addition of phenylsulfenyl chloride to norbomene is a particularly interesting example of the stability of the intermediate. Neither rearrangement nor syn addition products, which are observed with many of the other electrophilic reagents, are formed.63 This result indicates that the intermediate must be quite stable and reacts only by nucleophilic attack.64... 

Similarly to aromatic jt system, olefinic 7r-electron donors also readily react with bissulfonyl peroxides. Norbomene, when reacted with bis(arylsulfonyl) peroxides, gives a disubstituted product following Wagner-Meerwein rearrangement (equation 6). ... 

Although the gem-dihalocyclopropanes are fairly stable compounds, they can participate — as has been shown in the above sections — in quite a number of chemical transformations. Several reactions between dihalocarbenes and alkenes have been described in which no dihalocyclopropane formation could be observed that these intermediates might have been produced was only inferred from the type of products finally isolated. A typical process of this type is the e/ufo-addition of dihalocarbenes to norbomene and norbomadiene as discussed above. Comparable rearrangements have been observed, when dichlorocarbene additions either lead to aromatic products or when they cycloadd to rather inert aromatic systems. In the latter case a ring-enlargement takes place. A reaction related to the concerted opening of two cyclopropane rings in a bicyclopropyl system as discussed above takes place when dichlorocarbene is added to spiro[2.4]hepta-4,6-diene [227]. 

The reaction of norbomene yields the cis exo diester (equation 66).93 This exo isomer is not obtained directly by Diels-Alder chemistry. Other cyclic alkenes such as cyclopentene yield cis diesters, but isomers are obtained as a result of (3-hydride elimination-readdition from intermediates such as (23) prior to CO insertion (equation 67). Thus the palladium walks around the ring to some extent, but always stays on the same face. The extent of rearrangement can be minimized by higher CO pressures since CO insertion becomes more competitive with (3-elimination. This rearrangement becomes a critical problem in the dicarboxylation of 1-alkenes, since a variety of diesters are formed and the reaction is not particularly useful. These reactions were carried out with catalytic amounts of palladium and stoichiometric amounts of copper chloride. 

Acetoxylchlorination of norbomene (75), followed by skeletal rearrangement of 76 in an excess of Q1CI2, gives exo-2-chloro-syn-7-acetoxynorbornane (77). This is a good synthetic method for yyn-7-norbomenol (78) [67]. Similarly, the brendane... 

Norbomene adds to photolytically produced ethoxycarbonylnitrene specifically at the exo face the same aziridine is produced in the thermal addition of ethoxycarbonyl azide, but via the triazoline rather than the nitrene, with much imine by-product. There can be problems of selectivity and rearrangements when one reacts ethoxycarbonylnitrene with more complex substrates, e.g. alkenic steroids. Ethoxycarbonylnitrene via a-elimination) adds to vinyl chlorides to give 2-chloroaziridines, which can be rearranged thermally to yield 2-chloroallyl carbamates. This nitrene also adds to enamines, giving an array of rearranged products. A modem discussion of the reactivities of ethoxycarbonylnitrene (electrophilic) in comparison with phthalimidonitrene (nucleophilic) towards alkenes of different electronic properties has tqipeared. ... 

The reaction of norbomene with diethyl and diphenyl diazenedicarboxylate and dibenzoyl-diazene gives e.vo-oxadiazines 1 with unspecified yields25. The absence of rearranged products was assessed by experiments on 2,3-dideuterionorbornene. However, at least three other unidentified products were observed in the crude reaction mixture obtained with diethyl diazenedicarboxylate26. 

In a novel combination of Pauson-Khand cycloaddition with vinylcyclopropane chemistry, de Meijere has described an entry to linearly fused triquinanes beginning with cyclopropylalkynes. Cyclopentenone formation has been carried out with a variety of substitution patterns on the cyclopropane, and moderate yields achieved with both norbomene and cyclopentene as substrates. Thermal vinylcyclopropane-cy-clopentene rearrangement of the cycloaddition products leads to the final tricyclic system (Scheme... 

AUylic oxidation. Cyclohexene is oxidized to cyclohex-2-enyl acetate in 75% yield by the reagent at 70° when catalyzed by potassium bromidefea. 8 hr.). The reaction is slow in the absence of a catalyst. Norbomene is unreactive, but bicyclo[3.2.noclene-2 is oxidized rapidly to about an equal mixture of endo- and cxo-bicycIo[3.2.1]oct-3-ene-2-yl acetates. Acyclic olefins or cyclic olefins prone to allylic rearrangement give a complex mixture of allylic acetates. 

Previous routes to such compounds have included dehydration of 2-(j8-hydroxyethyl)imidazoles [55] (or dehydrobromination of the analogous bromoethyl compounds), pyrolysis of 2-(5-norbomen-2-yl) imidazoles [57] or thermal rearrangement of 1 -vinylimidazoles [58],... 

Fascinating rearrangements of aziridines have been applied to the synthesis of diterpene alkaloids by Wiesner and co-workers (Scheme 40). For example, the ester 217, prepared from cyclopentadiene carboxylate (215) and the benzyne precursor 216 by a Diels-Alder reaction, was converted to the aziridine 218 by treatment with benzenesulfonyl azide in 83% yield. When the aziridine 218 was heated with water for 24 h, the hydroxy ester 219 was obtained in 97% yield subsequent oxidation with the Jones reagent afforded the ketone 220. This rearrangement is analogous to that of the benzenesulfonylaziridine of norbomene. ... 

Addition of mercury(II) nitrite, generated in situ from mercury(II) chloride and sodium nitrite, provides a general route to 1-nitroalkenes. Thus, on treatment with sodium hydroxide or a tertiary amine the adducts are converted into nitroalkenes in good yields. The clean formation of 2-nitronorbomene from norbomene indicates that carbonium ion rearrangement is not a problem. A further point of interest is the regioselectivity of nitromercuration, illustrated by the nitration of (42 Scheme 3). The nitromercura-... 

The carbocations generated by nonKolbe electrolysis can rearrange by alkyl, phenyl or oxygen migration. Some examples are given in Table 11. The carbocations generated from exo- or en[Pg.653]

More remote substituents may also participate in epoxide opening/rearrangement. Christol and coworkers examined several S,(6)-substituted-2,3-norbomene ejco-oxides under acidic conditions, and found that certain 5-endo substituents played a part in oxirane opening. For example, oxa rings were formed in reactions of substrates bearing 5-entfo-methoxycarbonyl or -hydroxymethyl groups. A novel 1,4-migration of chloride was also detected (equation 28). ... 

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