Reductive Cyclization of o- Ethylamino nitrobenzene Derivatives

Catalytic hydrogenation or chemical reduction with concomitant cyclization has been used to convert several types of such nitro substrates into a variety of quinoxalines. The following examples, classified according to type of substrate, illustrate the possibilities available. 

1 -(A-Acetonyl-A-benzenesulfonylamino) -fluoro-2-nitrobenzene somewhat similarly gave 6-fluoro-3-methylquinoxalme (Raney Ni, H2, AcOEt, 20°C, 5 min 22% aerial aromatization ).  

1 -Chloro-3- [(1 -ethoxycarbonyl-1 -methylethyl)amino] -4-nitrobenzene (61) gave 6-cbloro-3,3-dimetbyl-3,4-dibydro-2(lF/)-quinoxalinone (62) (TiCl3, AcONa, 

In contrast, o-(A-etboxalyl-A(-propylamino)nitrobenzene (63) gave l-bydroxy-4-propyl-2,3(l//,4F/)-quinoxalinedione (65), perhaps via tbe partly reduced substrate (64) [Pd/C, Hj (3 atm), MejNCHO, 3 b 85%) likewise, 1-(etboxalylamino)-3-fluoro-6-nitrobenzene (66) gave 6-fluoro-l-bydroxy-2,3(l//,4fl)-quinoxalinedione (67) (Zn, NH4CI, HaO-MeaNCHO, 35°C, 57%) and tbe 4-bydroxy isomer was made in even better yield using hydro- 

Also many other examples,including some solid-phase syntheses. 

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