Optimization of the reaction conditions^a.

Entry	Variation of standard conditions	Yieldb	D-Inc.c
1	None	75%	96%
2	With 1a-Nad	75%	77%
3	With 1a-Ke	75%	83%
4	4-(4-Methoxyphenyl)butanoic acid and CsOHf	57%	60%
5	PC-I instead of PC-III	4%	—
6	PC-II instead of PC-III	3%	—
7	2b instead of 2a	Trace	—
8	2c instead of 2a	23%	96%
9	2d instead of 2a	14%	96%
10	Without PC-III or light	N.D.	—
11	Without 2a	5%	—

^a 1a-Cs (0.2 mmol), PC-III (1 mol%), 2a (10 mol%), DCM/D₂O (4 : 1, v/v; 2 mL, 110 eq. of D₂O), 45 W blue LEDs, room temperature, 18 h.

^bMeasured by GC using acetophenone as the internal standard due to the high volatility.

^cDeuterium incorporation was determined by HRMS-ESI.

^dSodium 4-(4-methoxyphenyl)butanoate.

^ePotassium 4-(4-methoxyphenyl)butanoate.

^fCsOH (2.0 equiv.) as the base. DCM = dichloromethane, N.D. = not detected.