Table 1.

Formation of 2a in the photochemical reaction of 1a under the various conditions^a.

entry	solvent	concentration of 1a (mM)	temperature (°C)	yield of 2a (%)b
1	benzene	80	15	18
2	benzene	800	15	8
3	benzene	8	15	17
4	toluene	80	15	16
5	CH2Cl2	80	15	10
6	CH3CN	80	15	10
7	benzene	80	50	5
8	toluene	80	−35	18
9	toluene	80	−75	14

^aThe photochemical reactions of 1a were performed for 4 h with a high-pressure Hg lamp (300 W) with a Pyrex filter under a dry nitrogen atmosphere in dried and degassed solvent. ^bThe yields of 2a were determined on the basis of ¹H NMR (500 MHz) peak areas; error ± 3%. Dimethyl fumarate was used as an internal standard.