D-2-symmetric chiroporphyrins derived from (1R)-cis-hemicaronaldehydic acid: Preparation and spectral characterization

Esters, N,N-disubstituted amides, and a N-acylurea derived from the enantio pure industrial intermediate (1R)-cis-hemicaronaldehydic acid (or biocartol ) are convenient synthons for the preparation of a series of chiroporphyrin s by condensation with pyrrole. These chiral meso-tetracyclopropylporphyrin s are obtained exclusively as the D-2-symmetric alpha, beta, alpha, beta at ropisomer, generally in low to moderate yields (2-20%), and in the urea cas e in excellent yield (60%). Hydrolysis of the urea substituents affords a c hiroporphyrin with mono-hi-substituted amide groups. H-1-NMR spectroscopy i ndicates that the eater, amide, and urea stereogenic groups sit on the porp hyrin close to the metal binding site and restrict substrate or ligand acce ss along a C-2-symmetric groove. This structural feature of chiroporphyrins and of their metal complexes is of high potential interest in asymmetric c atalysis and chiral recognition.