Synthesis of some analogues of cytisine: unusual reduction pathways for tertiary nitro groups in sterically constrained molecules

Abstract

The naphthalene derivative 4 was converted into the dinitro compound 5 by a ‘double Mannich’ reaction. Reduction of the compound 5 with tributylstannane gave the hydroxylamines 6 and 7 in low yield. Treatment of 5 with methanethiolate in DMSO gave the sulfides 8, 9 and/or 10 in varying ratios, depending on the reaction conditions. Raney nickel reduction of 10 gave the cytisine analogue 1. Similarly the dinitroquinoline 13 was converted into the dinitro compound 14. Treatment of 14 with sodium methanethiolate gave a mixture of the sulfides 15–17. Reduction of the compounds 16 and 17 with Raney nickel gave the pyridoazocine 2. The mechanisms of formation of the hydroxylamines 6 and 7 and the sulfides 8–10, 15–17 are discussed.