Table 3.

Influence of temperature on the Diels-Alder reaction.

entrya	reaction temperature [°C]	reaction time [h]	yield [%]b	ee [%]c
1	23	1	84	30
2	0	24	96	29
3	−20	24	98	31
4	−40	48	96	36
5	−70	96	71	39

^aAll reactions were carried out using 0.1 mmol maleimide 2a, 1.1 equiv anthrone (1a) and 0.1 (entry 1–4) or 0.25 equiv (entry 5) of 8c in 1 mL abs. dichloromethane. ^bIsolated yield after column chromatography. ^cEnantiomeric excess was determined by HPLC using Chiralpak IA column.