Nucleophilic addition polycyclic systems

Intramolecular oxidative cyclizations in the appropriately substituted phenols and phenol ethers provide a powerful tool for the construction of various practically important polycyclic systems. Especially interesting and synthetically useful is the oxidation of the p-substituted phenols 12 with [bis(acyloxy)iodo]-arenes in the presence of an appropriate external or internal nucleophile (Nu) leading to the respective spiro dienones 15 according to Scheme 6. It is assumed that this reaction proceeds via concerted addition-elimination in the intermediate product 13, or via phenoxenium ions 14 [18 - 21]. The recently reported lack of chirality induction in the phenolic oxidation in the presence of dibenzoyltar-taric acid supports the hypothesis that of mechanism proceeding via phenoxenium ions 14 [18]. The o-substituted phenols can be oxidized similarly with the formation of the respective 2,4-cyclohexadienone derivatives. 

Synthesis of selenocyclopropanes has rarely been carried out by routes that result in formation of a bond between selenium and a cyclopropyl carbon atom. The few exceptions that exist involve polycyclic systems containing a cyclopropane moiety. When (l ,la 8,9b)8)-l-chloro-la-trimethylsilyl-1a,9b-dihydrocyclopropa[/lphenanthrene was stirred in a tetrahydrofuran solution of potassium /crr-butoxide and potassium benzeneselenolate a complex reaction mixture was obtained, from which la-phenylseleno-1a,9b-dihydrocyclopropa[/]phenanthrene (1) and (la,laa,9ba)-l-phenylseleno-1a,9b-dihydrocyclopropa[/]phenanthrene (2) were isolated in 10 and 15% yield, respectively, by preparative TLC. Both selenocyclopropanes arise from the same intermediate, la//-cyclopropa[/]phenanthrene, which means that the addition of benzeneselenolate to this alkene is nonregioselective. In contrast, the nucleophilic addition of meth-... 

The cyclopropylmethyl subunit can be incorporated into a polycyclic system. Thus, endo-3-metalated nortricyclenes 6 were obtained from norbomadiene complexes 4 of platinum or palladium via exo addition of nucleophiles and intramoleeular alkene insertion converting the homoallylic subunit to a cyclopropylmethylmetal complex (see also Seetion 5.2.6.2.)... 

The susceptibility of nucleophiles to ring-opening reactions is often increased after the activated cyclopropane structure has been incorporated into a polycyclic system due to the additional strain. 3-enaqueous tetrahydrofuran. When 3-cnt/o-methoxytricyclo[3.2.0.0 ]heptan-6-one was dissolved in methanol, the corresponding ring-opened dimethoxy derivative 22 (R = Me) was isolated in high yield. 

Stereoselective, conjugate allylation of more remote positions using allyl trimethylsilane and TiCE is possible. Further transformation by nucleophilic addition and ringclosing metathesis affords fused polycyclic ring systems (Scheme 88). Stabilized anions and organocopper see Copper Organowetallic Chemistry) reagents also participate in Michael-type additions to complexed a ,/3-unsaturated aromatic enones. 

The major application of arynes in synthesis is in the construction of polycyclic systems using either the Diels-Alder or intramolecular nucleophilic addition reactions. 

Another widely used comparison, especially in bicyclic systems, is the exojendo rate ratio. This comparison is also fraught with pitfalls. Problems arise because the endo and exo isomers of a polycyclic system have unique configurations and hence different steric requirements. This can affect anchimeric assistance by neighboring groups. In addition there are inherent differences in field effects and nucleophilic solvent assistance. The 350-fold difference in rate constant for acetolysis of exo- and endo-2-norbornyl p-bromobenzenesulfonates [(11) and (12), respectively] was taken as evidence for a participation in the solvolysis of (11) by Winstein... 

Formation of cationic T -dienyliron complexes by proton addition to (Ti -diene)iron complexes with an additional conjugated double bond can also be applied to acyclic systems. Monocyclization and polycyclization reactions proceed by nucleophilic addition of pendent double bonds to the complexes. " - " ... 

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