Table 1. Initial catalyst screening using TKP 4a.

Entry	Catalyst	Temp	Solvent	Time a	6a b [%]	er c
1	5a	RT	CH2Cl2	20	94	82 : 18
2	5b	RT	CH2Cl2	20	91	25 : 75
3	5c	RT	CH2Cl2	20	98	31 : 69
4	5d	RT	CH2Cl2	20	99	96 : 4
5	5d	RT	THF	20	98	95 : 5
6	5d	RT	Toluene	20	98	94 : 6
7	5d	RT	MeCN	20	99	94 : 6
8	5d	0 °C	CH2Cl2	60	99	98 : 2
9	5d	0 °C	CH2Cl2	120	91 d	97 : 3
10	5e	0 °C	CH2Cl2	60	82	2 : 98

^aMinutes.

^bIsolated yield after chromatography.

^cDetermined by HPLC analysis.

^dReaction conducted using 1 mol% catalyst.