Carbon monoxide with aromatic rings

Sodium or potassium phenoxide can be carboxylated regioselectively in the para position in high yield by treatment with sodium or potassium carbonate and carbon monoxide. Carbon-14 labeling showed that it is the carbonate carbon that appears in the p-hydroxybenzoic acid product. The CO is converted to sodium or potassium formate. Carbon monoxide has also been used to carboxylate aromatic rings with palladium compoimds as catalysts. In addition, a palladium-catalyzed reaction has been used directly to prepare acyl fluorides ArH —> ArCOF. ... 

The reaction of alkenes with alkenes or alkynes does not always produce an aromatic ring. An important variation of this reaction reacts dienes, diynes, or en-ynes with transition metals to form organometallic coordination complexes. In the presence of carbon monoxide, cyclopentenone derivatives are formed in what is known as the Pauson-Khand reaction The reaction involves (1) formation of a hexacarbonyldicobalt-alkyne complex and (2) decomposition of the complex in the presence of an alkene. A typical example Rhodium and tungsten ... 

When benzyne is generated in the absence of another reactive molecule it dimerizes to biphenylene.132 In the presence of dienes, benzyne is a very reactive dienophile and [4+2] cycloaddition products are formed. The adducts with furans can be converted to polycyclic aromatic compounds by elimination of water. Similarly, cyclopentadienones can give a new aromatic ring by loss of carbon monoxide. Pyrones give adducts that can aromatize by loss of C02, as illustrated by Entry 7 in Scheme 11.9. 

In the case of the gem diester (121), the major pathway results in aromatization of the dihydropyran ring with production of the pyrylium species (121a). This is derived from the [M - C02Et]+ ion with subsequent loss of carbon monoxide and elimination of ethanol. It was shown that RDA fragmentation of (121), a minor pathway only, is a thermally induced process (72CJC1539). 

The aromatic borepins and benzoborepins have been prepared primarily as compounds of theoretical interest and no significant applications have been reported to date. Saturated 1-alkylborepanes, such as 23 and similar large ring boron compounds, are of use primarily as precursors in the synthesis of cyclic ketones by treatment with carbon monoxide followed by alkaline hydrogen peroxide <1982JOC1792>. 

Partial hydrogenation of aromatic rings can also be accomplished with catalysts such as [Co2(CO)g] under an atmosphere of carbon monoxide and hydrogen, but the isolated benzene nucleus cannot be re-duced. ° Anthracene (57), naphthacene, perylene (61) and pyrene (63) are converted to 9,10-dihydroan-thracene (60), 5,12-dihydronaphthacene, 1,2,3,10,11,12-hexahydroperylene (62) and 4,5-dihydropyrene (64), respectively. 

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