Identification of decomposition products of tropyl azide and interaction of tropylium ion with nucleophiles

An investigation of the structures of several of the products resulting from the decomposition of tropyl azide (I) and of the chemistry of related processes has been undertaken. Irradiation of samples of (I) in the vapor phase with low intensity UV G.E. Sun Lamps furnished a low melting white solid identified as tropyl troponimmonium azide (II). Earlier experiments of a similar nature reported to furnish (III) were not repeatable (Chem. Commun 276 (1967))... Upon standing, solutions of (I) slowly formed troponimmonium azide (IV) in the cold (J. Chem. Soc. (D), 220 (1970)). The structures (II) and (IV) were confirmed by conversion to the corresponding fluoborates and comparison with samples prepared by the methods of Bauld (J . Amer. Chem. Soc 89, 6763 (1967)) and Dauben (ibid. 89, 6764 (1967)). The nature of amine-tropylium ion interactions was investigated. The conclusions reported by P. B. Shevlin (Ph.D. Dissertation, Yale University, 1967) was at variance with those of D. S. Wulfman (Ph. D. Dissertation, Stanford University, 1962) and with those obtained in these laboratories as well as those reported by several other workers. We postulate, in contrast with Shevlin, that tropylium salts form at least 2 and possibly 4 different complexes with pyridine, none of which involves formation of a tightly held sigma complex in which an N-tropyl pyridinium species is present. Similar behavior was noted for 3,5 di-methyl pyridine. With 2 and 4 methylated pyridines, apparently C alklation occurs. In these instances no evidence of reversible complex formation was observed. Re-examination of dimethyl sulfoxide as a solvent for such studies reaffirmed the findings of Wulfman that sigma complex formation with solvent molecules occurred and precluded its use for equilibrium studies. In hopes of gaining insight into the amine processes, the synthesis of a series of tropyl acetates (acetate, chloracetate, dichloracetate) was undertaken. Only in the unsubstituted case was ester formed. In all cases tropone was obtained in fair yield. Only in one case was some tropilidene obtained. The mechanisms of these transformations are discussed --Abstract, pages iii-iv