Indolyl substituted 4-oxobut-2-enoic acids. Synthesis and aza-Michael additions

The synthesis of three new substituted 4-hetereoaryl-4-oxobut-2-enoic acids with indole ring substitutedin positions 3-, 5- and 7- is described. The addition of these Michael acceptors to 4-(1-phenylsulphonylpyrrol-3-yl)-4-oxobut-2-enoic acid in conjugate addition was explored using both racemic and chiral amines. In tandem with the crystallization-induced asymmetric transformation (CIAT) protocol the effective methodology for the synthesis of enantiomerically highly enriched substituted 2-amino-4-heteroaryl-4-oxobutanoic acids as multifunctional homotryptophan analogues was developed.