1,3-Dipolar Cycloaddition of 2,6-Dichlorobenzonitrile Oxide to 2-Methyl-N-confused Porphyrin. Regio- and Stereoselective Synthesis and Structural Characterization of 2-Aza-21-carbabacteriochlorin and Resolution of 2-Aza-21-carbachlorin Enantiomers

The 1,3-dipolar cycloaddition reaction of 2-methyl-N-confused porphyrin with 2,6-dichlorobenzonitrile oxide yielded four isomeric monoadducts of carbachlorin type and one diadduct of carbabacteriochlorin type. Two major carbachlorin products, constituting 82% of the monoadducts, were shown to be structural precursors of the unique 2-aza-21-carbabacteriochlorin. Enantiomers of the most abundant isomer of 2-aza-21-carbachlorin (55% of all carbachlorin products) have been resolved. The crystal structures of 2-aza-21-carbabacteriochlorin and the most abundant isomer of 2-aza-21-carbachlorin were characterized by X-ray diffraction.