Alkenes polycyclic

Various aspects of the ROMP of norbomene and its derivatives have been covered in Ch. 1, 3, 4, 10, 11, and 12. Here we shall give a general survey of the types of polycyclic alkene that imdergo ROMP, taken in order of ring size of the unsaturated ring see also Feast (1995). 

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Similar intramolecular Heck reactions with Pd(OAc)2 and a base (KOAc) or a phosphine have been reported by two other groups.78 These conditions also result in two isomeric polycyclic alkenes. 

The solvent could also exhibit a strong influence in these reactions. Thompson and coworkers [266] have shown that the hydrogenation of a polycyclic alkene on Pt/C is greatly dependent on the... 

The availability of 18 in one synthetic step via direct oxidative functionalization of HCTD [19-21] allows exploration of this valuable compound s chemistry, for the first time. Thus, the reaction sequence shown in Scheme 9 has been utilized to prepare a novel polycyclic alkene, 30, whose s unmetry properties require that its central, tetrasubstituted C=C double bond be completely planar (in the isolated molecule). The constraints imposed by the polycarbocyclic cage framework cause the CCC bond angles about the central C=C double bond in 30 to deviate significantly from the preferred value of 120°, thereby introducing additional steric strain in this molecule beyond that which is associated with its framework alone. 

As noted earlier, many bicyclic and polycyclic alkenes undergo hydroxymeicuration-demeicuration. Norbomene and derivatives328 give cis adducts, but less strained alkenes afford the expected trans adducts. 

The stereochemistry of addition to acyclic, cyclic and polycyclic alkenes is essentially identical to that of hydroxymercuration wherever the two processes have been compared. Fewer data have been accumulated for alkoxymercuration however. 

There is one known exception to the trans nature of the addition a hindered polycyclic alkene where a cis addition occurs. More recently, small proportions of cis adducts have been detected as minor components in additions to cyclohexenes. An inmresting recem usage of the INs-alkene reaction is in the azirine synthesis of Scheme 87. ... 

Anti-Bredt alkene a polycyclic alkene that contravenes Bredt s rules by having a C=C bond attached to a bridgehead carbon atom... 

Many examples of polycyclic alkene osmylations have been reported in the literature in connection with the syntheses of specific target molecules such as alkaloids, prostanoids, or steroids. However, carefully determined diastereomer ratios are usually not available. Due to the varied nature of these substrates, it is not possible to formulate definite rules for diastereo-face differentiation except in specific cases. Thus, for example, the exclusive exo reactivity of bridged systems such as bicyclo[2.2.1]heptene derivatives (norbornene-type) is well known as Alder s rule of exo addition63. 

Skeletal rearrangements are rare, but are found for strained bi- and polycyclic alkenes, e.g., bullvalene , bicyclo[4.2.2]deca-2,4,7,9-tetraene , 4,5-exo-trimethylene-2-norbornene , 6-methylenebicyclo[3.1.1]heptane ", 5-methylbicyclo[2.1.1] hexene N-benzyl-9-aza-bicyclo[4.2.2]deca-2,4,7-triene , dibenzobicyclo[2.2.2]-octatriene derivatives and bornylene ... 

The involvement of trimethylenemethane diradicals in deazetization of diazoalkane-allene adducts or trimethylene diradicals in the deazetization of the adducts of acyclic alkenes often leads to mixture of regioisomers and stereoisomers and from the standpoint of cyclopropane syntheses, this is undesirable. Far fewer problems of this type attend deazetization of the adducts of cyclic or polycyclic alkenes and, furthermore, even a modest amount of strain in the system activates the alkene to diazoalkane addition so that there is no need for activating substituents on the double bond. Cyclopropene is highly reactive towards diazoalkanes (see also Section 1.1.5.1.5.3.1.) and cycloaddition reactions of this type provide a ready entry into the bi-cyclo[1.1.0]butane series. The addition of diphenyldiazomethane to cyclopropene gave 4,4-diphenyl-2,3-diazabicyclo[3.1.0]hex-2-ene (1), which on photolysis gave a mixture of 2,2-diphenylbicyclo[1.1.0]butane (2) and 1,1-diphenylbuta-l,3-diene (3). ... 

It is one example of an important group of reactions between triazolediones and polycyclic alkenes. Related syntheses in this group are summarized in Table 6. In each case, carbenium ion rearrangements, like that for benzvalene, lead to urazoles which on conversion to the five-membered ring diazene and deazetization generated a three-membered ring. 

Table 6. Cyclopropyl Derivatives by the Dipolar Addition of 4-Methyl- or 4-Phenyl-l,2,4-triazole-3,5-dione to Strained Polycyclic Alkenes ...

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