Table 1.

Benzylic oxidation of (−)-homopterocarpin (4).

Entry	Conditionsa		Yield 3b	Yield 21b
1	Pb(OAc)4,	DCM/HOAc	0%	0%
2	KMnO4,	Amberlite CG-120, tBuOH/DCM/H2O	0%	0%
3	KMnO4,	NEt3, H2O/CHCl3, H2SO4	0%	0%
4	KMnO4,	0.1 eq. Bu4NHSO4, KOH, DCM/H2O	0%	0%
5	CAN,	(Me3tacn)RuCl3.H2O (0.1 equiv.), AgClO4 (0.4 equiv.), tBuOH/H2O 6:1, 30 °C	≈15%	0%
6	CAN,	MeCN/H2O 1:1	≈16%	0%
7	O2,	NHPI (0.2 equiv.), Co(OAc)2 (0.05 equiv.), MeCN	22%	–c
8	O2,	NHPI (1.0 equiv.), Co(OAc)2 (0.5 equiv.), MeCN, 0 °C; then PPh3, Ar	64%	10%
			>99% eed	91% eed

^aReactions were performed at room temperature if not stated otherwise.

^bIsolated yield.

^cNot determined.

^dDetermined by chiral HPLC.