Properties and Structure of the Anhydro-Bases

When a jo /r-A-alkylcarbolinium salt, unsubstituted at the ind-N atom, is treated with strong alkali, a yellow to deep orange, strongly basic solid separates. Although such products almost invariably give poor microanalytical values they can be shown to be derived from the quaternary hydroxide by loss of a molecule of water—hence the name anhydro-bases or anhydronium bases.All four carbolines form anhydro-bases e.g., j9 /r-A-methyl-j8-carbolinium iodide (419) gives 420. Most of the evidence bearing on the structures of these bases has been summarized, and discussion will therefore be limited to a few of the recent aspects of the chemistry of these compounds. 

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Support for this suggestion comes from many quarters. Reduction of the jS-carboline anhydro-bases with sodium and alcohol or with tin and hydrochloric acid gives the 1,2,3,4-tetrahydro derivatives, as does catalytic reduction over platinum oxide in an alkaline medium. On the other hand, catalytic reduction with platinum oxide in acetic acid results in the formation of the 5,6,7,8-tetrahydro-j3-carbolinium derivatives (see Section III,A,2,a). It should be noted, however, that reduction of pyrido[l,2-6]indazole, in which the dipolar structure 211 is the main contributor to the resonance hybrid, could not be effected with hydrogen in the presence of Adams catalyst. 

Protonation and alkylation of the anhydro-bases (e.g. 425) takes place at the ind-N atom (see Section IV, A, 2). The resulting ind-N-, j92/r-A-dialkylcarbolinium salts (e.g. 426) give the corresponding 

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