Abstract
Macrocyclizations in exceptionally good yields were observed during the self-condensation of N-benzylated phenyl p-aminobenzoates in the presence of LiHMDS to yield three-membered cyclic aramides that adopt a triangular shape. An ortho-alkyloxy side chain on the N-benzyl protecting group is necessary for the macrocyclization to occur. Linear polymers are formed exclusively in the absence of this Li-chelating group. A model that explains the lack of formation of other cyclic congeners and the demand for an N-(o-alkoxybenzyl) protecting group is provided on the basis of DFT calculations. High-resolution AFM imaging of the prepared molecular triangles on a calcite(10.4) surface shows individual molecules arranged in groups of four due to strong surface templating effects and hydrogen bonding between the molecular triangles.
Highlights
S hape-persistent macrocycles[1−4] are of special interest due to their rigid backbone, which often leads to selfaggregation into columnar stacks, and that can be eventually used for transport and separation processes[5,6] or as rigid scaffolds with well-defined cavities for catalytic or biomimetic applications.[7,8]
The formation of 2a diminished until a linear polymer was the only product, whereas the yield of 2b was hardly affected
The formation of 2 was rather surprising because it has been previously shown that the macrocyclization of methyl N-(2,4dimethoxybenzyl)-4-aminobenzoate in the presence of LiHMDS to form 2 was unsuccessful, most probably because of the deactivation of the methyl ester by the aminyl anion.[18]
Summary
S hape-persistent macrocycles[1−4] are of special interest due to their rigid backbone, which often leads to selfaggregation into columnar stacks, and that can be eventually used for transport and separation processes[5,6] or as rigid scaffolds with well-defined cavities for catalytic or biomimetic applications.[7,8]. Such a synthesis is often obstructed by formation of undesired side products, low reaction yields, and the need for high-dilution conditions.[9,10] highly efficient preparations of macrocycles have become the subject of considerable importance.
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