Substrate scope with respect to β-naphthols^a.

^aReaction conditions: 1 (0.12 mmol), 2a (0.10 mmol), A8 (10 mol%) and pyridine (2.5 mol%) in toluene (1 mL). Isolated yields based on 2a. The ee values were determined by chiral HPLC. The reaction time at −60 °C was given.

^bConducted at −50 °C.

^cConducted at −45 °C. For the cases of 3c–3g, 2.0 mol% pyridine was used.