Table 1.

Effects of reaction conditions on the synthesis of the intermediate 3.

Entry	Catalyst	Condition	Yield/%
1	no	100 °C for 11 h	hardly react
2	l-proline	100 °C for 11 h	66
3	l-proline	70 °C for 2 h, further 100 °C for 9 h	79
4	l-proline	70 °C for 3 h, further 100 °C for 7 h	73
5	l-proline	80 °C for 2 h, further 100 °C for 9 h	75