3,5 CYCLOHEXADIENE-1,2-DICARBOXYLIC ACID

In the case of 1,3-cyclohexadiene with Me2Zn, the dicarboxylation afforded the /rdicarboxylic acid 96 (Scheme 33). In contrast, when Ph2Zn was used instead of Me2Zn as a transmetallation agent, the phenylative carboxylation occurred in high regio- and stereoselectivity to give the l,4-m-substituted-2-cyclohexene 97, as a result of reductive elimination from the phenyl-7r-allylnickel intermediate, prior to the second carboxylation reaction (Scheme 33).47... 

A parallel electrooxidation of cis- or trans-cyclohexene-4,5-dicarboxylic acids would thus be expected to produce 1,4-cyclohexadiene, eqn 7. 

The reduction of aromatic carboxylic acids by Na(Hg) may take place in the nucleus or in the carboxyl group. Phthalic acid is reduced to m w-3,5-cyclohexadiene-l,2-dicar-boxylic acid [102] or 2,5-cyclohexadiene-l,2-dicarboxylic acid [103], whereas certain phenolic carboxylic acids may be reduced to aldehydes. 

Ozonolysis as used below is the oxidation process involving addition of ozone to an alkene to form an ozonide intermediate which eventually leads to the final product. Beyond the initial reaction of ozone to form ozonides and other subsequent intermediates, it is important to recall that the reaction can be carried out under reductive and oxidative conditions. In a general sense, early use of ozonolysis in the oxidation of dienes and polyenes was as an aid for structural determination wherein partial oxidation was avoided. In further work both oxidative and reductive conditions have been applied . The use of such methods will be reviewed elsewhere in this book. Based on this analytical use it was often assumed that partial ozonolysis could only be carried out in conjugated dienes such as 1,3-cyclohexadiene, where the formation of the first ozonide inhibited reaction at the second double bond. Indeed, much of the more recent work in the ozonolysis of dienes has been on conjugated dienes such as 2,3-di-r-butyl-l,3-butadiene, 2,3-diphenyl-l,3-butadiene, cyclopentadiene and others. Polyethylene could be used as a support to allow ozonolysis for substrates that ordinarily failed, such as 2,3,4,5-tetramethyl-2,4-hexadiene, and allowed in addition isolation of the ozonide. Oxidation of nonconjugated substrates, such as 1,4-cyclohexadiene and 1,5,9-cyclododecatriene, gave only low yields of unsaturated dicarboxylic acids. In a recent specific example... 

G. Kresze, E. Kysela, and W. Dittel, Polyhydroxyamines via Diels-Alder synthesis with nitroso compounds. V. l,3-Cyclohexadiene-5,6-dicarboxylic acid derivatives as reactants, Liebigs Ann. Chem., 210 (1981). 

Homophthalic acid esters from 1,3-cyclohexadienes and allene-l,3-dicarboxylic acid esters... 

Carboxy-5-methyl-4-oxo-2,5-cyclohexadien- 1-ylidene) 2,3,6-trichlorophenyl)methyl -2-hydroxy-3-methylbenzoic acid, 9CI. 2",5",6"-Trichloro-4-hydroxy-3,3 -dimethylfuchsone-5,5 -dicarboxylic acid. C.I. Mordant blue 47. C.I. 43855. Radiochrome blue B. Diamond blue FBG. Sunchromine blue FBG. Mitsui chrome brilliant blue GX... 

The intramolecular Diels-Alder cyclization of cyclohexadiene-l,2-dicarboxylic anhydride-derived diester-tethered triene (86) produces the cycloadducts in a ratio of 7 1 (Scheme 31). The intramolecular Diels-Alder reactions of amino acid-derived trienes (87) yield cycloaddition products (88) and (89) which are mainly cw-fused and derived from the exo-transition states (Scheme 32). A key reaction in the synthesis of the natural product momilactone A is the transannular Diels-Alder cyclization of the trans-trans-cis alkene (90) to the trans-syn-trans tricycle (91) (Scheme 33). The Diels-Alder cycloaddition of 1 l-oxapentacyclo[6,5,2,2 0 0 ]-heptadeca-4,14,16-triene-4,5-dicarboxylic anhydride (92) with cyclopentadiene proceeds with 5yn-facial selectivity to produce syn,endo and syn,exo cycloadducts (93) and (94)... 

A soln. of 4-methyl-4-dichloromethyl-2,5-cyclohexadien-l-one in abs. methanol and dimethyl acetonedicarboxylate added to a soln. of Na in abs. methanol, and refluxed 2 hrs. dimethyl 9-methy 1-9-dichloromethylbicydo [3.3.1 ]nona-3,7-dione-2,4-dicarboxylate (Y 63.2%) dissolved in glacial acetic acid, treated with coned. H2SO4, and refluxed 10 hrs. 9-methyl-9-dichloromethylbicyclo-[3.3.1]nona-3,7-dione (Y 84.0%). H. Stetter and J. Mayer, B. 92, 2664 (1959). 

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