A Series of Model Compounds for the Study of Aromatic Reactions

Abstract

A series of halogenated phthalides \vas prepared in xhich there \vas a systematic variation in the identity, position, and degree of activation of the halogen, and in the activation of the methylerle group. A study was made of the selective reductive removal of halogen in the presence of another halogen, or of a nitro group.i\Ietameconine (Ia) is admirably adapted to the study of competitive reactions. A rapid survey of its possibilities has shown that in several well-ltno\vn aroinatic reactions it could be used to drive currently favored theories into difficulties that were not easily resolved (1). The new colnpounds described in this paper formed a weapon that has since been used in a much Inore intensive attack upon two of these reactions.One of these was the copper-catalyzed removal of halogen by aqueous hydroxide ion. Our previous work (1-6) had provided a set of compounds superbly suited to the study, a s she\\-n by the large number of new observations recorded in the next paper. RIore coinpounds needed in the investigation were provided in the present work. In particular, the synthesis of IIb, 116, and IId was saved froin triviality by two difficulties that had to be overcome. I t was pointed out previously (1) that the nitro group in 4-amino-7-nitrometameconine (IIe) was very easily extruded on diazotization. For example, when IIe was diazotized in dilute aqueous hydrochloric acid, reduction of the diazonium solution gave 7-chloron~etan~econine (IIIa), and treatment of the diazonium solution wit11 potassiulll iodide gave 4-iodo-7-chlorometan~econine (IIId) (1). The same diazonium solution has now been sho\vn to give 4,7-dichlorometameconine (IIIb) with cuprous chloride. Hou~ever, cuprous bromide gave a mixture of compounds instead of pure 1116. Thus the diazonium cation IIIe was conventional in its relative reactivities towards chloride, bromide, and iodide under the conditions used.