Table 1. Solvent, Temperature, and Substituents Effects on the Uncatalyzed Reaction between 1 and 2^a.

				conversion (%)
entry	substrate	T (°C)	solvent	1 h	2 h	4 h
1	1a	rt	toluene	4	6	10
2	1a	rt	DCM	2	4	7
3	1a	rt	THF	5	6	9
4	1a	rt	iPrOH	7	11	20
5	1a	rt	tBuOAc	5	8	11
6	1a	rt	anisole	3	4	7
7	1a	rt	DMC	2	3	6
8	1c	rt	toluene	4	6	8
9	1f	rt	toluene	5	9	14
10	1h	rt	toluene	2	6	10
11	1i	rt	DCM	1	2	4
12	1j	rt	DCM	2	3	4
13	1l	rt	toluene	27	48	76
14	1l	0	toluene	3	6	12
15	1l	–10	toluene	2	3	5
16	1n	rt	toluene	11	21	32
17	1o	rt	toluene	2	3	5

^aAll reactions were carried out with 20 mol % excess of aldehyde, 0.5 M concentration, and the conversion was monitored by HPLC. The reported data are a selection of a more extended screening (see Supporting Information).