Norbomadienes acidity

When irradiated in stronger acid (FHSO3) at —60°, the tropylium ion is seen to isomerize cleanly to the norbomadien-7-yl cation (7) (Childs and Taguchi, 1970 Hogeveen and Gaasbeek, 1970). The ion 7 has been shown to be photochemically stable (Cabell and Hogeveen, 1972). However, it is known to revert to the tropylium ion thermally at temperatures above 45° (Lustgarten et al., 1967). 

The magnesium complex 34 was demetalated with trifluoroacetic acid to produce the H2[pz(A3B1)] (35) (98%) followed by conversion into the corresponding copper complex Cu[pz (A3B x)] (36, 95%) with Cu(II) acetate. Alternatively, Compound 36 can be prepared directly from the magnesium complex 34 by treatment with trifluoroacetic acid in the presence of Cu(II) acetate (72%). All forms of the norbomadiene substituted pz precursors, M[pz (A3Bj)] A = dipropyl, B = benzonorbomadiene M = Mg, H2, Cu, 34-36, have... 

Glycine acts as an acid-base catalyst in this reaction. C8 and Cl 1 are very acidic, and once deprotonated they are very nucleophilic, so they can attack C2 and C3 in an aldol reaction. Dehydration gives a key cyclopentadienone intermediate. (The mechanism of these steps is not written out below.) Cyclopentadienones are antiaromatic, so they are very prone to undergo Diels-Alder reactions. Such a reaction occurs here with norbomadiene. A retro-Diels-Alder reaction followed by a [4 + 1] retrocycloaddition affords the product. 

In a study of the addition of nitrosyl chloride or nitrosyl bromide to norbor-nene and norbomadiene, it was observed that (a) there was no structural rearrangement during the reaction, (b) a cis addition had taken place, (c) nucleophilic solvents such as ethanol or acetic acid were not incorporated in the products. These facts seem to speak against an ionic addition mechanism, while a free radical initiated by NO radicals was considered unlikely since nitric oxide is inactive toward norbomadiene. Therefore a four-center mechanism has been suggested [70], However, when a relatively simple, unstrained olefin such as A9-octalin was subjected to the reaction, only blue, crystalline, monomeric 9-nitroso-10-chlorodecalin was produced. This product had a trans configuration. Thus it is evident that the structure of the olefin has a significant bearing on the steric course of the addition [71]. 

The cyclobutane derivative (55) gave an optical yield of 91% in the hydrogenation of a-acetamidocinnamic acid. The catalyst was here prepared in situ from [RhCl(l,5-hexadiene)]2. The corresponding 1,2-derivative of cyclopentane gave an optical yield of only 73% and the cyclopropane and cyclohexane derivatives gave 15% and 36% respectively.235 [RhCl(cod)2] in presence of the norbomadiene-based ligand NORPHOS (56) gave up to 96% optical yields with a-acetamidocinnamic acid as substrate.236... 

Acetylene Polymers Homopolymers of optically active acetylenes, including (/ )-153 synthesized by [RhCl(norbomadiene)]2 catalyst, show intense CD bands in the UV-visible region, probably based on a predominant helical sense of the main chain [204]. Excess single-handed helicity of the main chain can be induced for polymers of achiral acetylenes (154 and 155) by adding chiral molecules. The chiral induction is based on acid-base interaction or complex formation between the polymer and the additives [205-2081. 

This method is applicable to the efficient synthesis of 2,5-norbomadiene, which can be obtained in low yield by anodic decarboxylation of 5-norbomene-2,3-dicarboxylic acid (equation 43)47. 

Norbomadiene reacted with diethylphosphonochloridite [ClP(OEt)2] to afford phosphinate ester 150 and it was characterized by single crystal diffraction analysis <1996JHC979> the Lewis acid, POCl3 accelerated the reaction. Reaction of bispyrrolylpropane 175 with PBr3 led to the formation of bromophosphine derivative, which proved to be thermally unstable and was further converted to phosphate 176 with water <1999CHE1383>. 

Dibromo-8-telluratricyclo[2.2.1.1]octane 8,8-Dibromide4 1.84 g (20 mmol) of norbomadiene are dissolved in 150 ml of diethyl ether and the solution is cooled to 0°. 3.20 g (20 mmol) of tellurium tetrabromide are dissolved in 20 ml of concentrated hydrobromic acid and added dropwise to the stirred norbomadiene solution. The mixture is stirred for 4 h, the organic phase is separated, dried with anhydrous magnesium sulfate, and evaporated yield 1.02 g (9.5%) in.p. 116°. 

Finally, we describe the two syntheses of [3]peristylane 403) reported by Garratt and White.369 This hydrocarbon is constructed of three cyclopentane rings which are mutually fused in a manner which also generates a cyclopropane ring. Subsequent to the conversion of norbomadiene to endo-3-carboxybicyclo[3.2.1 ]oct-6-ene 401) by an established route,370 this acid was reduced and reoxidized to the aldehyde level (Scheme 65). Pyrolysis of the sodium salt of the corresponding tosyl-... 

Remote double bonds often participate in epoxide openings, sometimes with extensive skeletal changes. ejco-Norbomadiene oxide (15 equation 6) provides an interesting example. Meinwald et alP found that this very acid-sensitive material rearranged simply on standing to give the endo-aldehyde (17), presumably via the intermediate nortricyclanol ion (16). 

The cycloaddition between cyclopentadiene and Bu3SnC=CCHO can be catalysed by a chiral Lewis acid to give the norbomadiene with 80% ee, and then reactions at the stannyl group can lead to the synthesis of other chiral bicycloheptadienes 74... 

The photoisomerisation kinetics and other properties of the 1 1 inclusion complexes formed between aromatic derivatives of norbomadiene and P-cyclo-dextrin have been measured." (S)- or (R)-2-Chloropropiophenone affords partially racemised (S)- or (R)-2-phenylpropionic acid respectively by a photo-induced rearrangement via what is probably an ion or radieal intermediate," and (Z)-N-substituted benzoyl-a-dehydrophenylalanines such as (7) are photo-isomerised to 1-azetidine derivatives (8) by a 1,3-acyl migration. Irradiation of 9,9 -bifluorene-9,9 -diol (9) gives a mixture of fluoren-9-one and spiro[9H-fluorene-9,9 (10 -H)-phenanthren]-10 -one (10) whose composition is solvent dependent with the more polar solvents favouring (10). Laser flash photolysis shows the presence of two transients, one of which can be identified with the 9-fluorenyl cation (11), and which originates from photoheterolysis of the diol (9). There is also evidence to support the view that unimolecular rearrange-... 

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