Table 1.

Optimization of α-carboxylation of N-benzylpiperidine in continuous flow.

Entry*	Equiv KOCOCF3	Pressure† (MPa)	tR (min)	UV filter	Yield 2a+3a (%)‡	Regioselectivity (2a/3a)‡
1	0	0.69	5	none	21	6.6:1
2	1	0.69	5	none	45	33:1
3	3	0.34	4	none	78	30:1
4	3	0.34	10	> 280 nm	92	52:1

^*Reactions were carried out using the original photochemistry system (entry 1–3) or using Beeler's photochemistry system (entry 4). See Supplementary Fig. 1 and 2 for details of the setup.

^†Pressure of BPR. 0.69 MPa is equivalent to 7.3 equiv of CO₂ and 0.34 MPa to 3.6 equiv.

^‡Calculated by gas chromatography (GC) after esterification with (trimethylsilyl)diazomethane, using methyl benzoate as an internal standard.

DMF, N,N-dimethylformamide; t_R, residence time.