A reductive dehalogenation of substituted 1,lO-phenanthrolines has also been n~t e d .~~~ Catalytic hydrogenation of 1,lO-phenanthroline with Raney nickel catalyst by a method similar to that adopted by Searles and Warrens for the reduction of 4,7-phenanthroline (2) afforded 1,2,3,4-tetrahydro-l,10-phenanthroline (1) in 80 % yield when the hydrogenation was carried out at 58 lb/sq in pressure at 20" for 40 h. There was no evidence for the formation of the 5,6-dihydro derivative analogous to (3) although Searles and Warrens obtained both (4), in 40 % yield, and (3), in 44 % yield, from the similar reduction of 4,7-phenanthroline. The structure of (1) was confirmed by elementary analyses and n.m.r. spectroscopy and by characterization of the derived hydrobromide salt. Hensen and Trobsl did not analyse compound (1) but characterized it by way of the dihydrochloride salt and the picrate. The tetrahydro-1,lOphenanthroline (1) afforded 1-acetyl-1,2,3,4,-tetrahydro-1,lO-phenanthroline by
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