HOMOLYTIC MECHANISMS OF AROMATIC REARRANGEMENTS .2. THERMAL REARRANGEMENTS OF 1-ALKYLPYRIDINIUM SALTS (LADENBURG REARRANGEMENT)

The products formed during the thermal rearrangements of 1-alkylpyridinium iodides at 300° in sealed tubes (Ladenburg rearrangement) have been shown to consist of the hydriodides of the original bases, their alkylated derivatives, and binuclear bases including bipyridyls and dipyridylalkanes, together with hydrocarbons derived from the 1-alkyl substituents by gain or loss of hydrogen atoms. The pronounced directing influence towards α- and γ-positions of the pyridine ring associated with this reaction has been confirmed. On the basis of these and other results, a mechanism is proposed which involves the homolytic dissociation of the nitrogen-alkyl bond, and in the case of the iodides also depends on their existence partly as charge-transfer complexes.