Aromatisation of gem-substituted hydroaromatic compounds by highpotential quinones has been shown to be accompanied by a Wagner-Meerwein rearrangement. The reaction has been tested for a number of monoand bi-cyclic systems and for several related compounds in the aliphatic series. Syntheses of some new hydroaromatic compounds and naphthalenes are described.THE evidence, accumulated in earlier papers (Parts 11,2 111,3 X,4 and XI l), concerning the mechanism of dehydrogenation of hydroaromatic compounds by quinones has strongly favoured a two-step ionic process involving a carbonium ion as intermediate. Viewed in this light the reaction is seen to possess the characteristics of a unirnolecular eliminationIn the dehydrogenation the leaving group is the hydride ion (H-), and the qilinone assumes the r6le of solvent or electrophilic catalyst in effecting the ionisation. Unimolecular elimination is, of course, but one of a number of reactions which a carbonium ion intermediate may undergo.6 Thus substitution, both intra-and inter-molecular, as well as a variety of rearrangements may compete with the simple elimination process. It is therefore to be expected that hydrogen-transfer to quhones of high potential should be capable of considerable elaboration in that, for certain donor structures, reactions more subtle than the conventional dehydrogenation might occur. This has been found to be so, and in this and the following three papers some alternative transfer reactions are examined.The present paper describes hydrogen-transfers which are accompanied by a Waver-Meerwein rearrangement. In particular, consideration is given to the dehydrogenation of hydroaromatic systems in which aromatisation is formally '' blocked " by gemsubstituents (dialkyl, diaryl, or arylalkyl). Two examples have been the subject of a preliminary report,s and the conversion of 1,l-dimethyltetralin (I) into 1,2-dimethylnaphthalene (11) by high-potential quinones illustrates the process. The course of this reaction is in direct contrast to that followed by the conventional methods of dehydrogenation. Catalytic dehydrogenation, as well as dehydrogenation by elemental sulphur and selenium, usually results in the elimination of a blocking substituent.' Some exceptions to this general rule have been noted by Adkins et aL8 but even in these cases, which involve the use of a specially prepared nickel-kieselguhr catalyst, the rearrangement is by no means the.exclusive reaction. We have now examined the dehydrogenation of a wide range of gem-substituted hydroaromatic compounds by quinones and found that C , 91.3; H, 8.7y0), isolated as its orange-red $icy& (from ethanol), m. p.
