Condensation of the quinoxaline aldehyde (I) with (S)-4-bromo-alpha-methylbenzylamine (II) produces imine (III). To this is added phosphinic acid dimethyl trimethylsilyl ester, generated in situ from dimethyl phosphite and chlorotrimethylsilane, to furnish the alpha-amino phosphonate (IV). Finally, hydrolysis of the methyl phosphonate and methoxy groups of (IV) under acidic conditions leads to the title compound