Quinoxalinones cyclization

A,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%]. " °... 

Methyl-3-(2,3,4-trihydroxy- l-phenyUiydrazonobutyl)-2( 1 //)-quinoxalinone (186) gave 3-(5-acetoxymethyl-1 -phenylpyrazol-3-yl)-1 -methyl-2( 1 //)-qui-noxahnone (187) (neat AC2O, reflux, 3 min 80% note additional acetyla-tion) ° also analogous cyclizations. ... 

Styryl-2(l//)-quinoxalinone (29) underwent a one-pot thiation and cyclization to give 2-phenylthieno[2,3-/7]quinoxaline (30) (P2S5, pyridine, reflux, 10 h 55%). ... 

The use of diamine 27, bearing a fluorous-Boc protecting group, has been used with microwave irradiation in an Ugi/de-Boc/cyclization strategy for the synthesis of benzimidazoles 28 and quinoxalinones 29 [64]. Compared to the original procedures, which take 1-2 days, this approach avoids the use of... 

Furthermore, multicomponent reactions can also be performed under fluorous-phase conditions, as shown for the Ugi four-component reaction [96], To improve the efficiency of a recently reported Ugi/de-Boc/cyclization strategy, Zhang and Tempest introduced a fluorous Boc group for amine protection and carried out the Ugi multicomponent condensation under microwave irradiation (Scheme 7.84). The desired fluorous condensation products were easily separated by fluorous solid-phase extraction (F-SPE) and deprotected by treatment with trifluoroacetic acid/tet-rahydrofuran under microwave irradiation. The resulting quinoxalinones were purified by a second F-SPE to furnish the products in excellent purity. This methodology was also applied in a benzimidazole synthesis, employing benzoic acid as a substrate. 

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