Table 2.

Optimization of the catalyst.

Entry	Catalyst	DFE yield (%)	Entry	Catalyst	DFE yield (%)
1	4a	2.08	10	4j	7.62
2	4b	5.41	11	4k	6.46
3	4c	7.85	12	4 l	1.41
4	4d	13.30	13	4 m	17.92
5	4e	3.55	14	4n	16.46
6	4 f	3.97	15	4o	16.73
7	4 g	4.90	16	4p	14.06
8	4 h	14.58	17	4q	14.20
9	4i	13.09	18	4r	26.90

^*Reaction conditions: FA (10 mmol), catalyst (0.1 mmol), toluene (10 mL), 100 °C and 7 h. GC yield.