Having identified the optimal reaction conditions, we first explored the scope of the enantioselective addition of Grignard reagents
2a with various chromone esters (
Scheme 3). The 2-ethyl and
tert‑butyl ester chromone could afford the corresponding products
3b and
3c in similar results, while isopropyl ester gave the tetra-substituted chromanones
3d in relatively lower yield and ee even using 1.0 mol% catalyst. Two more active substrate bearing trifluoroethyl and trichloroethyl groups were also amenable to this reaction, generating the products
3e and
3f in excellent yields (95%−96%) and enantioselectivities (92%−94%). Furthermore, the benzyl ester and its analogues 4-methylbenzyl, 4-nitrobenzyl ester derived chromones also proceeded smoothly to produce the desired products with high to excellent yields and
ee (
3g–
3i, 89%−98% yields, 88%−94%
ee). Next, a wide range of 2-methyl ester chromones containing diverse substituents at different positions on the phenyl ring underwent the conjugate additions in the same reaction condition. In general, electron-donating groups give better yields and
ee compared with electron-withdrawing groups at the same position. 2-Methyl ester chromones bearing electron-donating groups (−Me and OMe) and electron-withdrawing groups (−F, Cl and Br) at C6-position on the benzene ring were suitable substrates for this reaction, affording the desired products
3j−
3n in moderate to high yields (33%−90%) and excellent
ee (90%−94%). Functional ester group at the same position was also accommodated, although a relatively lower
ee was obtained (
3o, 64% yield, 84%
ee). Next, substituents (−Me, vinyl, F and Cl) at C7-position of 2-methyl ester chromones were also investigated, and similar results were obtained compared with the C6-substituted substrates (
3p−
3s, 76%−97% yields, 88%−93%
ee). Although the
ee value could be maintained using C8 methyl substituted chromones (
3t, 91% yield, 94%
ee), only moderate
ee were obtained when electron-withdrawing groups (−F, Cl and Br) were introduced at the same position of chromones (
3u−
3w, 84%−91% yields, 67%−77%
ee). Lastly, the more challenging C5-substituted chromones were explored in this reaction. Although both fluorine and methyl substituents decrease the reaction yields, the enantioselectivities remained high to excellent (
3x−
3y, 48%−57% yields, 81%−90%
ee). It is noteworthy that both di-substituted and phenyl-fused chromones were also applicable to this reaction, providing the corresponding products
3z−
3ab in high to excellent yields (78%−97%) and
ee (86%−92%).