Absolute stereochemical determination of chiral carboxylic acids.
Monoamidation of 1,4-diaminobenzene with alpha-chiral carboxylic acids leads to a carrier strategy for absolute stereochemical determination with bis-zinc porphyrin tweezers by exciton-coupled circular dichroism (ECCD). The helicity induced in the porphyrin tweezers upon complexation with the derivatized carrier originates from the preferred conformation of the C(carbonyl)-C(chiral) bond. Correct ECCD signs can be predicted by the rotamer that places the large group perpendicular to the carbonyl group with the small group facing the porphyrin. [reaction: see text]