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Incremental Introduction of Organocatalytic Activity into Conformationally Engineered Porphyrins
Author(s) -
Kielmann Marc,
Grover Nitika,
Kalisch Werner W.,
Senge Mathias O.
Publication year - 2019
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201801691
Subject(s) - chemistry , bifunctional , organocatalysis , imine , amine gas treating , stereochemistry , density functional theory , molecule , computational chemistry , combinatorial chemistry , enantioselective synthesis , catalysis , organic chemistry
To study the correlation of macrocycle nonplanarity and catalytic activity of free base porphyrins in detail, a series of six tetraphenylporphyrins with graded degree of β‐ethyl substitution (“H 2 Et x TPPs” 1 – 6 ; x = 0, 2, 4, 6, 8) was applied in organocatalyzed reactions. The macrocycles display incrementally increasing nonplanarity due to repulsive peri ‐interactions. This creates an out‐of‐plane vector and better accessibility of the core amine and imine groups as the number of alkyl substituents increases. Following such a molecular engineering approach, the inner core system could be used to activate small molecules as a result of significant saddle distortion. The potential organocatalyst “H 2 Et x TPPs” were used in benchmark sulfa‐Michael reactions and we found a distinct relationship between nonplanarity and conversion. These observations were attributed to the combined effect of enhanced basicity and increased H‐bonding potential that could facilitate bifunctional organocatalysis. Ultimately, density functional theory (DFT) calculations were performed on 1 – 6 to monitor some electronic properties of the title compounds.