Syntheses of heterocyclic aromatic compounds via organoiron and organochromium chemistry

Abstract

In studies aimed at the synthesis of potential antitumour compounds (η6-dibenzodioxin)Cr(CO)3 was prepared by employing dibenzodioxin in a direct thermal complexation reaction with hexacarbonylchromium. Double nucleophilic substitution reactions between (η6-1,2-dichlorobenzene)CpFe+ and substituted 1,2-benzenediols were carried out under mild conditions to prepare (η6-dibenzodioxin)iron complexes functionalized in the 1- or 2-position with an alkyl, aldehyde, acid, alcohol, ester, or amide group. 3-Methyl- and 4-methyl-(1,2-dichlorobenzene)iron complexes were reacted with substituted 1,2-benzenediols to effect functionalization of both aromatic rings. The dibenzodioxin ligands were liberated readily by irradiation with ultraviolet light. Reactions of the non-complexed dibenzodioxins, including deprotonation with an alkyllithium reagent followed by quenching with a variety of electrophiles, yielded further derivatives. Organoiron chemistry has also been the key feature in investigations of the synthesis of a functionalized diphenyl ether known to be thyromimetic and hypocholesterolaemic. Thus, the oxygen nucleophiles phenoxide and 4-methylphenoxide displaced chloride from (η6-1,4-dichlorobenzene)CpFe+ under mild conditions to give the corresponding η6-diphenyl ether cationic complexes. In contrast, a hard carbanion derived from 3-ethoxy-6-methylpyridazine-1-oxide added ortho to an electron-withdrawing group of (η6-1,4-dichlorobenzene)CpFe+ (and other η6-chloroarene cationic complexes) in a Yanovsky-type reaction to from a neutral η5-cyclohexadienyl ligand.