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.