Cyclization of o- Ethylamino aniline Derivatives

The cyclization of several types of these derivatives is illustrated in the following examples. 

3-Nitro-6-(prop-2-ynylamino)aniline (19, R = H) gave 2-methyl-7-nitroquinoxa-line (20, R = H)[(MeCN)4CuBF4, PhMe, 85°C, 20 h 75% aerial oxidation ] 2,6-dimethyl-7-nitroquinoxaline (20, R = Me) was made similarly (78%). ° 

4-Bromo-6-(2-chloroethylamino)-l,3-benzenediamine (21) gave 7-bromo-l,2,3,4-tetrahydro-6-quinoxalinamine (22) (Na2C03, Me2NCHO, reflux, 1 h 85%). ° 

2-Bromo-A -ferf-butyl-6-(2-chloroacetamido)aniline (25) gave 5-bromo-4-tert-butyl-3,4-dihydro-2(l//)-quinoxalinone (26) (EtPrjN, Nal, MeCN, reflux, 22 h 79%).  

A-Dibenzyl-2-(ethoxycarbonylmethyl)amino-4-(trifluoromethyl)aniline (27) underwent reductive debenzylation and spontaneous cyclization to 6-trifluoro-methyl-3,4-dihydro-2(17/)-quinoxalinone (28) [Pd(OH)2/C, EtOH, H2 (3 atm), 3 days 97%]. ° 

Such direct cyclizations usually occur in basic media to afford quinoxaline /V-oxides. For success, C2 in the ethyl group needs to be a carbonyl entity or to be suitably activated. The following examples illustrate this valuable route to such /V-oxides (and thence to quinoxalines see Section 4.6.2.1). 

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