Wydział Chemii

Anna Berlicka

Lechosław Latos-Grażyński

Ludmiła Szterenberg

Miłosz Pawlicki

2010

European Journal of Organic Chemistry

5688-5695

10.1002/ejoc.201000792

Naukowa

Angielski

Artykuł

The oxidative degradation of the contracted carbaporphyrinoid 3,8,13,18‐tetraphenyldithiaethyneporphyrin, which contains an acetylene moiety embedded in the macrocyclic framework, was investigated. The light‐induced, regioselective cleavage of the macrocyclic ring was observed during exposure to dioxygen affording four open‐chain diastereomers terminated by carbonyl groups. Studies on the regioselectivity of the process showed that the thiophene was cleft together with the 8‐aryl substituent, which proved the primary attack of dioxygen at the C8–C9 bond. Diastereomers {4Z,10E}, {4Z,10Z}, {4E,10E}, and {4E,10Z} [the arrangement with respect to C4–C5 and C10···C13 conjugated bonds given] differ by the orientation of the terminal pyrrolone unit with respect to the 5‐phenyl substituent and by the geometry around the cumulene fragment. Thermal {4Z,10E}–{4Z,10Z} and {4E,10E}–{4E,10Z} isomerization was detected and was confirmed by exchange cross‐peaks in the ROESY map. The molecular structures of the {4Z,10E} and {4E,10E} stereoisomers were established by X‐ray analysis. Density functional theory (DFT) was applied to model the molecular and electronic structure of {4Z,10E}, {4Z,10Z}, {4E,10E}, and {4E,10Z}. The very small energy difference observed between suitable diastereomers accounts for their coexistence in solution (0.48 kcal/mol for {4Z,10E}, {4Z,10Z}; 0.63 kcal/mol for {4E,10E}, {4E,10Z}).

phorphyrinoids, photooxidation, Degradation, isomerization, cleavage reactions

https://doi.org/10.1002/ejoc.201000792

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