Abstract
The reactions of 4, 6-phenanthroline (I) and its N-oxides, 6-oxide (II) and 4, 6-dioxide (IV), with dimethyl sulfoxide were carried out in the presence of sodium hydride (or potassium tert-butoxide), and 3-monomethyl compounds (V, VI, and IX) were obtained from all the compounds. This reaction of the 4-oxide (III) resulted in deoxygenation of the N-oxide group to afford the 3, 5-dimethyl compound (VII) and 5-(methylsulfinyl)-methyl-4, 6-phenanthroline (VIII). The same reaction of 1, 10-, 1, 7-, and 4, 7-phenanthrolines (X, XI, XII) gave the 4-methyl compound (XVI) and 4, 7-dimethyl compound (XVII) from X, and the 4-methyl compound (XVII) and 7-(methylsulfinyl) methyl compound (XIX) from XI, while XII gave a polymer. The reaction of their N-oxides, 1, 10-phenanthroline 1-oxide (XIII), 1, 7-phenanthroline 1-oxide (XIV), and 4, 7-phenanthroline 7-oxide (XV), for 30 min resulted in liberation of the N-oxide group to form benzo [h] quinoline (XX) in the former two cases and benzo [f] quinoline (XXIII) in the latter case. Reaction of XIII for 4 hr resulted in the formation of compounds of XX methylated at the 6- or 5-position (XXI and XXII). The same reaction was carried out in an NMR sample tube, and it was shown that N-oxide liberation occurred in the reaction mixture ; the previously proposed reaction mechanism had to be corrected. Calculation of the reaction indices of 4, 6-phenanthrolines by Huckel's molecular orbital method gave values agreeing well with the experimental results.
