Table 1.

Optimization of U-5C-4CRconditions

Entry${}^{\mathrm{a}}$	Additive	Temperature	Time (days)	Conversion (%)${}^{\mathrm{b}}$
1	–	rt	1	30
2	–	rt	3	39
3	${\text{TEA}}^{\mathrm{c}}$	rt	3	12
4	${\text{FeCl}}_3^{\mathrm{d}}$	rt	3	53
5	${\text{TiCl}}_4^{\mathrm{d}}$	rt	3	67
6	${\text{TiCl}}_4^{\mathrm{d}}$	rt	5	65
7	${\text{TiCl}}_4^{\mathrm{d}}$	$-20{}^{\circ }\text{C}$	3	50
8	${\text{TiCl}}_4^{\mathrm{d}}$	$50{}^{\circ }\text{C}$	3	60

${}^{\mathrm{a}}$ Unless stated otherwise, the reactions were carried out in 0.1 M MeOH solutions on a 0.2 mmol scale. ${}^{\mathrm{b}}$ Estimated by HPLC. ${}^{\mathrm{c}}$ 1.0 eq. ${}^{\mathrm{d}}$ 5 mol%