Highly selective [4+4] cross-photodimerization of (4a-azonia)anthracenes driven by confinement of D-A hetero-guest pair in cucurbit[10]uril host

The cross-photodimerization often comes with the formation of undesired and competitive homo-photodimer as side products. Herein, we report a series of highly selective [4 + 4] cross-photodimerization between anthracene and 4a-azoniaanthracene derivatives within a cucurbit[10]uril (CB[10]) host in water. Heteroternary inclusion complexes were formed through encapsulation of donor (D1-D2, anthracene derivative) and acceptor (A1-A3, 4a-azoniaanthracene derivatives) pairs in CB[10]. In the presence of CB[10] (1.0 equiv.), the [4 + 4] cross-photodimerization between D1 and A1/A2/A3 efficiently gave a single racemic cross-photodimer. Furthermore, the cross-photodimerization between 9-substituted anthracene D2 and A1/A3 was catalyzed by CB[10] (0.1 equiv.) to quantitatively yield a cross-photodimer with high regioselectivity. Efficient formation of selective cross-photodimers could be attributed to the exclusive encapsulation of D-A hetero-guest pairs in CB[10] and the confinement effect of the CB[10] host cavity. Our study further proves host–guest complexation as a powerful strategy for cross-cycloaddition reactions with high efficiency.