1,5-Cyclooctadiene vinylic oxidation

The combination of probably the oldest synthetic procedure for formation of a triple bond, i.e., the dehydrobromination of a vinyl bromide, with modern crown ether chemistry has resulted in one of the simplest yet very powerful methods for making highly strained cycloal-kynes. Thus, 1,5-cyclooctadiyne (56) can be made by treating l,5-dibromo-l,5-cyclooctadiene (55) with potassium rerf-butanolate in nonpolar solvents in the presence of 18-crown-6 [3 b, 24]. The nonpolar solvent protects the bent triple bond from nucleophilic attack by tert-butanol (Scheme 8-5). 1,5-Cyclooctadiyne had previously been made in very low yield by dimerization of butatriene (57), which is not a readily accessible compound [25]. Other important 1,2-elimination reactions generating cyclic alkynes are the oxidative degradation of... 

Oxidative addition of allyl and vinyl ethers to zero-valent ruthenium complex also takes place under mild conditions. The reaction of Ru(cod)(cot) [cod = 1,5-cyclooctadiene, cot = 1,3,5-cyclooctatriene] with allyl phenyl ether or phenyl ortho-tolyl ether in the presence of PMea results in cleavage of the C-0 bond to give a (r -allyl)(aryloxo)ruthenium(II) complex, Ru(OAr)(r/ -C3H5)(PMe3)3 (Scheme 3.40) [77]. When allyl 2,6-xylyl ether is employed in this reaction, further C-H bond activation takes place to give an oxaruthenacycle... 

Rh(I) catalysts under H2 effect the reductive cychzation of diynes and enynes [119]. In the example below (1.39), Rh(C0D)20Tf (COD = 1,5-cyclooctadiene) is converted by H2 gas to a Rh hydride, which is thought to undergo oxidative cycliza-tion to produce a rhodacyclopentene intermediate. Cleavage of the Rh-C bonds by reductive elimination to form a vinyl rhodium species, and hydrogenolysis of that intermediate, forms the Rh hydride and the cychzed product. 

When conducting the ROMP of norbornene or cyclooctadiene in miniemulsions [82], two approaches were followed (i) addition of a catalyst solution to a miniemulsion of the monomer and (ii) addition of the monomer to a miniemulsion of Grubbs catalyst in water. With the first approach it was possible to synthesize stable latexes with a high conversion, whereas for the second approach particles of >400 nm were created, without coagulum, but with 100% conversion. Subsequently, a water-soluble ruthenium carbene complex [poly(ethylene oxide)-based catalyst] was prepared and used in the direct miniemulsion ROMP of norbornene [83], whereby particles of 200-250 nm were produced. The catalytic polymerization of norbornene in direct miniemulsion was also carried out in the presence of an oil-soluble catalyst generated in situ, or with a water-soluble catalyst [84] the reaction was faster when using the oil-soluble catalyst. Helical-substituted polyacetylene could be efficiently polymerized in direct miniemulsion to yield a latex with particles that ranged between 60 and 400 nm in size, and which displayed an intense circular dichroism [85] that increased as the particle size decreased. The films were prepared from dried miniemulsion latexes that had been mixed with poly(vinyl alcohol) (PVA) in order to conserve the optical activity. 

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