Pyrrolidine synthesis optimization^a.

Entry	Oxidant (equiv.)	Reductant	Solvent	Yieldb (%)
1	UHP (1.0)	B2pin2	TFE	71
2	UHP (1.2)	B2pin2	TFE	91
3	UHP (1.5)	B2pin2	TFE	70
4c	UHP (1.2)	B2pin2	TFE	0
5	30% aq. H2O2 (1.2)	B2pin2	TFE	84
6	UHP (1.2)	B2pin2	HFIP	70
7	UHP (1.2)	B2pin2	MeOH	30
8d	UHP (1.2)	B2pin2	TFE	33
9	UHP (1.2)	o-tolylB(OH)2	TFE	0
10e	UHP (1.2)	B2(OH)4	TFE	85f

^aConditions: amine 1a in solvent (0.1 M), then oxidant added, 50 °C, 16 h. Reductant then added (1.2 equiv.), rt, 30 min.

^{b 1}H NMR yield of 4a using 1,3,5-trimethoxybenzene as an internal standard.

^cB₂pin₂ and UHP added together.

^dReaction stirred at rt instead of 50 °C.

^eReduction step stirred at 50 °C, 1 h.

^fIsolated yield. B₂pin₂: bis(pinacolato)diboron. HFIP: 1,1,1,3,3,3-hexafluoroisopropanol.