Photoinduced molecular transformations. Part 143. (2 + 2) Photoaddition of 3-hydroxy-1-benzopyran-2-one, 3-benzyloxycarbonyloxy-1-benzopyran-2-one, and their 8-methoxy derivatives, with alkenes and formation of 1,2-disubstituted 1,2-dihydrofuro[2,3-c][1]benzopyran-4-ones by way of β-scission of cycl