Association constant K_a values^a of the chiral acceptor and 3-BARF pairs.

Entry	XB acceptor	K a, M−1
1	(R)-8	6.1 ± 0.7
2	(S)-8	6.0 ± 0.8
3	(R)-9	94 ± 7
4	(S)-9	91 ± 5

^aAssociation constant K_a measured in CDCl₃ at 298 K and determined by fitting the ¹H NMR titration data to 1 : 1 binding isotherm of BindFit.¹⁵ The given K_a and standard error are the calculated mean values of two parallel experiments. Full details given in the ESI.