Table 1 Optimization of reaction conditions^a

^aReaction conditions: (a) 1a (0.05 mmol), 2a (0.055 mmol), CPA (10 mol %), solvent (2 mL), rt, 40 h. 3aa was isolated for the second step. (b) toluene (1 mL), 100 °C, 20 h. ⁱPr = iso-propyl, ODCB = 1,2-dichlorobenzene, TBME = tert-butyl methyl ether. AcOⁱPr = iso-propyl acetate.
^bIsolated yields.
^cDetermined by chiral HPLC analysis.
^dStep b: TsOH·H₂O (1.0 equiv) was added in the second step at room temperature for 10 h.
^eThe 3aa was not isolated and TsOH·H₂O was added directly in one-pot.
^f7 d for step a.
^gSolvent (4 mL).

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