Scheme 3.

[2+2] Photodimerization of dibenzylideneacetone with sunlight:7 The presence of a Lewis acid leads to changes in the chemo‐ and regioselectivity.

[2+2] Photodimerization of dibenzylideneacetone with sunlight:7 The presence of a Lewis acid leads to changes in the chemo‐ and regioselectivity.