Design and synthesis of thiophene-based C₂-symmetric chiral phosphoric acids on a decahydroquinoxaline scaffold for stereoselective transformations

In this study, the design and the synthesis of a thiophene-based phosphoric acid based on a chiral decahydroquinoxaline scaffold derived from enantiopure trans-1,2-diaminocyclohexane was reported. This catalyst was then employed in stereoselective transformations such as the enantioselective Friedel-Crafts reaction of indoles with imines to afford 3-indolyl methanamines. High yields (up to 98%) and high enantioselectivities (up to 98% ee) were obtained. DFT calculations were performed to investigate the key transition states, providing mechanistic insight and confirming the origin and sense of the observed stereochemical outcome.