Table 1.

Optimization of the tandem CEYM–IMDAR.

entry	solvent	T (°C)	1a:2a	t (h)	additive	% yield 3aa
1	toluene	90	1:3	6	–	25
2	toluene	90	1:3	24	–	37
3	toluene	90	1:3	48	–	57
4	toluene	90	1:3	72	–	39
5	toluene	90	1:1	48	–	36
6	toluene	90	1:5	48	–	30
7	toluene	110	1:3	48	–	52
8	toluene	140	1:3	48	–	37
9	DCM	60	1:3	48	–	25
10	C6H5CF3	90	1:3	48	–	60
11	toluene	90	1:3	48	Ti(OiPr)4b	38
12	toluene	90	1:3	48	BF3·OEt2b	15
13	toluene	90	1:3	48	thioureac	49
14	toluene	90	1:3	48	BQb,d	37

^aIsolated yield after column chromatography. Variable amounts of 4a were observed in all cases, but never exceeded 15% (based on 2a). Some unreacted 2a was also detected in all cases; ^b5 mol %; ^c1 mol %; ^dbenzoquinone.