Cu–ABNO Catalyst\nfor the Synthesis of Quinolines\nand Pyrazines <i>via</i> Aerobic Double Dehydrogenation\nof Alcohols

In\nthis report, a new imidazole- and amide-functionalized pincer-like\nCu(II) complex (<b>1</b>) was synthesized and characterized.\nBy employing <b>1</b> and 9-azabicyclo[3.3.1]nonane <i>NH</i>-Oxyl (ABNOH), a catalytic protocol for alcohol oxidation\nand the subsequent alcohol oxidation-triggered synthesis of quinolines\nand pyrazines were explored. Alcohols such as 2-aminoaryl alcohols\nwere also oxidized efficiently. As carbonyls from 2-arylaminobenzyl\nalcohols and secondary alcohols are synthons for quinolines, we explored\ntheir synthesis directly from alcohols. The protocol was quite efficient\nand completed the reaction in only ∼5–10 h. Combinations\nsuch as (a) primary 2-arylaminobenzyl alcohols with secondary alcohols\nor their ketones and (b) secondary 2-arylaminobenzyl alcohols with\nsecondary alcohols or their ketones were found to be very effective\nfor the synthesis of quinolines. The protocol was also successful\nfor the synthesis of various pyrazines from 1,2-diols and 1,2-diaminobenzenes\nin 10 h. Mechanistic investigations showed that the generated complex\nacted as an active catalyst: it activated O<sub>2</sub> and subsequently\nwith the cooperation of 9-azabicyclo[3.3.1]nonane <i>N</i>-Oxyl (ABNO<sup>•</sup>) activated the α-CH hydrogen\nof coordinated alkoxide. Then, Cu(II)/Cu(I) reduction led to the formation\nof carbonyl compounds, which via successive C–C/C–N\ncoupling reactions resulted in heterocycles in the presence of KO<sup><i>t</i></sup>Bu and <b>1</b>.