Asymmetric Friedel–Crafts alkylation of activated benzenes with methyl (E)-2-oxo-4-aryl-3-butenoates catalyzed by [Pybox/Sc(OTf)3]

The asymmetric Friedel–Crafts reaction between methyl (E)-2-oxo-4-aryl-3-butenoates (1a–c) and activated benzenes (2a–d) has been efficiently catalyzed by the ScIII triflate complex of (40S,50S)-2,6- bis[40-(triisopropylsilyl) oxymethyl-50-phenyl-10,30-oxazolin-20-yl]pyridine (pybox 3). The 4,4-diaryl-2- oxo-butyric acid methyl esters (4) are usually formed in good yields and the enantioselectivity is up to 99% ee. The sense of the stereoinduction can be rationalized with the same octahedral complex (10) between 1, pybox 3 and Sc triflate already proposed for other reactions involving pyruvates, and catalyzed by the same complex.