Demjanov Rearrangement of 9-Xanthenemethylamine

Abstract

The ring expansion of xanthene derivatives to dibenz [b,f]oxepin is already known. Thus Anet and Bavin (1) have reported the synthesis of dibenz [b,f]oxepin and 10-methyldibenz [b,f]oxepin by Wagner-JlIeerwein rearrangement of 9-xanthenemethanol and 9-hydroxyinethyl-9-inethylxanthene. Store recently, Whitloclc (2) has reported the forination of dibenz [b,f]oxepin in 61yo yield \\-hen xantl~ylium perchlorate is treated with ethereal diazoinethane. We wish to report on the reaction of 9-xanthenemethylamine under the conditions of the Demjanov rearrangement (3), in I\-hich ring expansion has also been observed.9-Xantheneinethylamine (4, 5) was prepared from 9-xantheneacetic acid (6) in the follo\ving manner. The acid was converted into its acid chloride with tl~ionyl chloride and this in turn into the azide, which underwent Curtius rearrangeinent (7) to the isocyanate. Treatinent of the isocyanate \~i t h alkali, however, gave N,N1-di(9-xanthenemethy1)urea instead of the ainine. The forination of the urea was avoided by conversion of the crude isocyanate into the ethylurethane followed by hydrolysis of the urethane t o 9-xanthenemethylainine, which was isolated as the hydrochloride salt, in a yield of 41.5y0 based on 9-xantheneacetic acid. T h e yield was improved t o 52.5y0 by treatment of the crude isocyanate with benzyl alcohol followed by reduction of the benzylurethane to the ainine.9-Xanthenemethj~lainine was treated with nitrous acid in acetate buffer under experimental conditions norn~ally employed in the Deinjanov rearrangeinent. T h e crude product was worked up as described in the Experimental section and separated into an olefinic and a n alcoholic fraction by column chromatography on alumina. The alcoholic fraction, comprising 96yo of the product, was shown t o be a inixture of 9-xanthenemethanol and 10,ll-dihydrodibenz[b,f]oxepin-lO(l1,H)-01 in a ratio of 1:4. T h e ring-expanded alcohol is formed in an overall yield of 65% based on the ainine. T h e composition of the inixture was established by nuclear magnetic resonance (n.1n.r.) analysis of the mixture of the two alcohols and by partition chromatography on a silica gel column. T o carry out the analysis it was necessary to synthesize the two alcohols by established procedures and t o exainine their physical properties. 9-Xantheneinethanol was prepared by the method of Anet and Bavin (1) and 10,l 1-dihydrodibenz[b,f]oxepin-lO(l1 ,H)-01 by borohydride reduction of the corresponding oxepinone, which was prepared by the method of kIanslte and Ledinghain (8). The isomeric tertiary alcohol, 9-methyl-9-xanthenol, a possible product of this reaction, was also prepared (9), but its properties were such that its presence in the alcoholic fraction from the Demjanov reaction is precluded. We found that, when the tertiary alcohol was placed on an alumina column and chloroform applied t o the column, the recovered product was not the alcohol. The product showed no hydroxyl absorption in the infrared, and was not further examined.T h e foregoing results show tha...