Table 1 Condition optimization.^a

^aReaction conditions: 1a (0.3 mmol), 2a (0.1 mmol), amine catalyst (0.03 mmol), co-catalyst (0.03 mmol), basic additive (0.3 mmol), 4 Å MS (150 mg), solvent (1.0 mL) at 25 ^oC for 24 h. ^bIsolated yield of 3a. ^cThe er values were determined via HPLC on chiral stationary phase. ^dEDTA-4Na Ethylenediaminetetraacetic acid disodium salt. ^eAgOAc (0.05 mmol) was used as the co-catalyst, the mixture of EDTA-4Na (0.15 mmol) and p-phthalic acid (PTA, 0.12 mmol) was added as the basic additive, and the reaction was stirred for 48 h.

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