Table 1.

Optimization of Bicyclohexene [2 + 2]^a

entry	solvent	temperature	hv	5b	10 + 11b	4b
1	THF	27 °C	254 nm		60%
2	Et2O	27 °C	254 nm		86%
3	heptane	27 °C	254 nm		51%	7%
4	heptane	23 °C	dark	24%	46%c
5	heptane	−4 °C	dark	70%	2%c
6	heptane	−4 °C	254 nm	43%	39%	18%
7	toluene	−4 °C	254 nm	24%	46%	28%
8	benzene	−4 °C	254 nm	21%	37%	42%

^aReactions were conducted on 1 mmol scale in 1 mL indicated solvent.

^bYields calculated by comparison to ¹H NMR internal standard.

^cOnly 10.