Optimization of reaction conditions for intermediate 3a^a.

Entry	Ratiob	T (°C)	Time (min)	Yieldc (%)
1	1 : 1.2	130	30	40
2	1 : 1.2	140	30	55
3	1 : 1.2	150	30	76
4	1 : 1.2	160	30	79(60) d
5	1 : 1.2	170	30	64
6	1 : 1.2	160	10	66
7	1 : 1.2	160	20	76
8	1 : 1.2	160	40	71
9	1 : 1.0	160	30	75

^aThe reactions were carried out with 4 mmol of 2a under solvent-free condition.

^bThe ratio of 2a : 1.

^cThe yields of 3a were determined by ¹H NMR of the reaction mixture after work-up using 1,3,5-trimethoxybenzene as internal standard.

^dIsolated yield.