TY - JOUR
T1 - Structural study of the solid-state photoaddition reaction of arylidenoxindoles
AU - Milanesio, Marco
AU - Viterbo, Davide
AU - Albini, Angelo
AU - Fasani, Elisa
AU - Bianchi, Riccardo
AU - Barzaghi, Mario
PY - 2000/6/2
Y1 - 2000/6/2
N2 - The photochemistry of isomeric 2-furyliden- and benzylidenoxindoles (2H- indol-2-ones) is examined. In solution E-Z isomerization is the only process via the excited singlet state (which fluoresces in glassy solution at 77 K and not at room temperature). In the crystalline state, the two (Z) derivatives are photostable, in accordance with the prediction based on the structural determination of the furylidene derivative, which adopts the unreactive Schmidt's γ type arrangement. The (E) furylidene derivative (1a) gives efficiently (Φ = 0.3) the head-to-tail dimer, as indicated by the crystal structure, which is of the reactive α type, in full accord with the topochemical principles. In contrast, the corresponding benzylidene (1b) derivative reacts sluggishly (Φ < 0.01) and mainly gives polymers, despite the fact that crystal structure determination shows that it likewise pertains to the α type and complies with the topochemical rules. The difference in reactivity is explained on the basis of (i) the twist of the phenyl ring with respect to the indole plane, and (ii) the higher overall cohesion energy and the lower interaction energy between facing molecules, as found from the charge density analysis for the crystals of 1b in comparison to those of 1a. This evidences a further stringent requirement for the occurrence of topochemical photodimerizations.
AB - The photochemistry of isomeric 2-furyliden- and benzylidenoxindoles (2H- indol-2-ones) is examined. In solution E-Z isomerization is the only process via the excited singlet state (which fluoresces in glassy solution at 77 K and not at room temperature). In the crystalline state, the two (Z) derivatives are photostable, in accordance with the prediction based on the structural determination of the furylidene derivative, which adopts the unreactive Schmidt's γ type arrangement. The (E) furylidene derivative (1a) gives efficiently (Φ = 0.3) the head-to-tail dimer, as indicated by the crystal structure, which is of the reactive α type, in full accord with the topochemical principles. In contrast, the corresponding benzylidene (1b) derivative reacts sluggishly (Φ < 0.01) and mainly gives polymers, despite the fact that crystal structure determination shows that it likewise pertains to the α type and complies with the topochemical rules. The difference in reactivity is explained on the basis of (i) the twist of the phenyl ring with respect to the indole plane, and (ii) the higher overall cohesion energy and the lower interaction energy between facing molecules, as found from the charge density analysis for the crystals of 1b in comparison to those of 1a. This evidences a further stringent requirement for the occurrence of topochemical photodimerizations.
UR - http://www.scopus.com/inward/record.url?scp=0034595841&partnerID=8YFLogxK
U2 - 10.1021/jo991873i
DO - 10.1021/jo991873i
M3 - Article
SN - 0022-3263
VL - 65
SP - 3416
EP - 3425
JO - Journal of Organic Chemistry
JF - Journal of Organic Chemistry
IS - 11
ER -