The research was initiated by testing the model reaction of easily prepared 4-hydroxy-1-methylquinolin-2(1
H)-one (
1a) [
15] and (
E)-2-nitro-3-phenylallyl benzoate (
2a) [14a] in the presence of catalyst
5a (quinine) in PhCF
3 (1 mL) at room temperature. To our delight, the reaction ran smoothly to afford the desired tetrahydropyran fused quinolinone derivative
3a in 88% yield with 8:1 dr and 80%
ee (
Table 1, entry 1). Several catalysts (
Fig. 2), including H-bond donating bifunctional catalysts
5b and
5c, primary amine catalyst
5d and other natural cinchona alkaloids
5e,
5f and
5g were examined with the purpose of improving the stereoselectivity of this reaction (
Table 1, entries 2–7).
5e (quinidine) turned out to be the best catalyst for this reaction, as it gave the reaction in 90% yield 7:1 dr and 84%
ee (
Table 1, entry 5). Perhaps not surprised, catalysts
5a and
5e gave the product
3a in the opposite configuration. Subsequently, we screened different protecting groups of MBH esters
2 under room temperature with the aim of further improving the stereoselectivity by using catalyst
5e (
Table 1, entries 8–12). The reaction has good diastereo- and enantioselectivity with
p-nitrobenzoyl as protecting group (6:1 dr, 90%
ee), however low yield was observed (30%) (
Table 1, entry 9). To our delight, a considerable improvement in both the yield (85%) and dr (10:1) was achieved by replacing the protecting group with 2-naphthoyl, despite the slightly diminished
ee value (88%) (
Table 1, entry 12). Other protecting groups like acetyl or 2, 4, 6- trimethylbenzoyl were either gave the reaction in poor enantioselectivity, or in low yield (Table S1 in Supporting information). Taken yield, dr and
ee values into consideration, we choose 2- naphthoyl as the protecting group for further optimization. Next, solvents, reaction concentration, temperatures and time were screened by using catalyst
5e (
Table 1, entries 13–18). Finally, the best reaction condition was established as performing the reaction in dichloromethane at 0 ℃ for 72 h, with the concentration of 0.2 mol/L, and gave the reaction in 73% yield, 9:1 dr and 92%
ee (
Table 1, entry 16). The molecular structure and absolute configuration of the two chiral centers within (3
S, 4
R)-(-)-
3a were unambiguously determined by X-ray crystallography analysis (
Table 1, Fig. S3 in Supporting information), and the crystallographic data has been deposited in cambridge centre with CCDC 1912415.