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Synthesis of Functionalized, Sterically Congested Calix[4]phyrin Macrocycles Using Donor–Acceptor‐Substituted Cyclopropanes – First Example of a Mono‐ meso ‐spirolactone Incorporated into a Calix[4]phyrin
Author(s) -
Beyzavi M. Hassan,
Lentz Dieter,
Reissig HansUlrich,
Wiehe Arno
Publication year - 2013
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.201201295
Subject(s) - chemistry , steric effects , porphyrin , cyclopropane , aryl , alkyl , reagent , tetrathiafulvalene , acceptor , combinatorial chemistry , ring (chemistry) , stereochemistry , organic chemistry , molecule , physics , condensed matter physics
Calix[4]phyrins are an important class of hybrid macrocyclic systems at the interface between porphyrins and calixpyrroles (porphyrinogens). A new stepwise synthesis of oxidation‐resistant meso ‐hydrogenated calix[4]phyrins is reported, which allows variable substitution in the residues of their sp 2 ‐ meso ‐centers without the need for a porphyrin intermediate. It relies on the acid‐catalyzed condensation of a sterically hindered donor–acceptor‐substituted cyclopropane precursor with pyrrole to form a sterically congested dipyrromethane. This was subsequently condensed with a wide range of alkyl and aryl aldehydes bearing electron‐donating or electron‐withdrawing substituents followed by an oxidation step to form stable calix[4]phyrin( 1 . 1 . 1 . 1 )s with bridging meso ‐C H hydrogen atoms through an acid‐promoted dehydrative condensation. The methodology avoids any need for premetallation of the macrocycle and/or the use of organometallic catalysts or reagents and allows the incorporation of the bulky cyclopropane‐derived substituents specifically into the 5,15‐ meso ‐like positions. The resulting regioisomerically pure products display conformational features that reflect their mixed nature between porphyrins and calixpyrroles and they were assessed by X‐ray diffraction analysis, NMR techniques and UV/Vis spectroscopy. The possibility to introduce key functional groups enables subsequent modification of these calix[4]phyrins and allows their connection to other groups such as biologically active moieties. Of special interest is an unprecedented example of an acid‐driven lactonization that results in the incorporation of a mono‐ meso ‐spirolactone into a calix[4]phyrin( 1 . 1 . 1 . 1 ). Moreover, it is demonstrated that this approach to calix[4]phyrins is also applicable to other sterically congested dipyrromethanes.