1,2,3,4-Tetrahydroquinoxaline acylation

Quinoxaline gave l,4-diethyl-l,2,3,4-tetrahydroquinoxaline by indirect reductive alkylation (AcOH, KBHai, <15°C, 1 h, then reflux, 6h 87% presumably by nuclear reduction, A-acylation, and further reduction of the acetyl groups ). ... 

Although 1- and/or 4-acylated hydroquinoxalines might not be considered as regular quinoxalone ketones, they are included here for pragmatic reasons. Examination of the NMR chemical shifts for H5 and H8 in l,4-diacyl-l,2,3,4-tetrahydroquinoxalines (197, R = Me, Et, Ph, etc.) indicated that the endo-exo conformation (shown) predominated in most such compounds at ambient temperatures. " However, this was disturbed in l,4-dibenzoyl-6,7-dimethyl-l,2,3,4-tetra-hydroquinoxaline (198), which showed a predominance of the exo-exo conformation (shown) below the coalescence temperature. ... 

Hydroxyimino-l,2,3,4-tetrahydroquinoxaline in the presence of an acylating agent afforded l-oxo-4,5-dihydro-l,2,4-oxadiazolo[4,3-a]quinoxaline. The reaction of 2-aminobenzamide oxime in the presence of aldehydes leads to oxadiazoloquinoxalines . 

Zaragoza E, Stephensen H (1999) Solid-phase synthesis of substituted 4-acyl-l,2,3,4-tetrahydroquinoxalin-2-ones. J Org Chem 64(7) 2555-2557. doi 10.1021/... 

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