Table 2.

[2 + 2] Dimerization of aromatic alkenes via photoinduced electron transfer^a

Entry	Substrate	Electron relay	Product	Yieldb,c
1		0.5 equiv. naphthalene		54% (0%)
2		0.25 equiv. anthracene		46% (3%)
3		0.5 equiv. naphthalene		51% (30%)
4		0.5 equiv. naphthalene		42% (27%)
5d		3 equiv. propylene oxide		72% (0%)
6e		None		(62%)
7		0.25 equiv. anthracene		0% (0%)
8		None		(31%)
9f		0.25 equiv. naphthalene		78% (14%)

^aReactions carried out in 0.4 M degassed acetonitrile.

^bAverage of two isolated yields on a 100 mg scale.

^cParenthetical product yield in absence of electron relay.

^dReaction carried out at 0 °C in sparged dichloromethane.

^eReaction carried out at –10 °C in sparged dichloromethane.

^fReaction carried out at –10 °C in acetonitrile.