Benzochlorins, Naphthochlorins, Purpurins and Verdins

A very similar type of benzochlorin 50 was also synthesized by Smith s group as a result of the cyclization of the product obtained after Vilsmeier formylation reaction of Ni or Cu(OEP) using dimethylaminoacrolein and phosphorous oxychloride.The utility of this class of compounds as photosensitizers for PDT was first shown by Morgan et Jn a mouse tumor model. With a few 

One of the major problems associated with benzochlorin preparation is the difficulty in demetalation at the final step of the synthesis. Gunter et converted a series of Ni(II) 5,15-diphenylporphyrins 56 into the corresponding benzochlorins, which upon acid treatment produced the corresponding free-base analogue 57 in excellent yield. 

X-ray analyses of Ni(II) 5,15-diarylbenzochlorins showed a remarkable distortion in the ring, which possibly helped in the removal of the central metal ion. This methodology was later followed by Osuka et for preparation 

Gunter and Robinson reported the synthesis and spectroscopic properties of purpurins bearing functionality starting from 5,15-disubstituted mejo-[/S-(ethoxycarbonyl)vinyl] porphyrins 91.The meso-acrylate porphyrins were efficiently converted into the so-called type-A purpurins 92 under basic conditions. lype-B purpurins 93 were also formed, and the relative yields of types A and B are temperature and solvent dependent, but independent of the presence of oxygen. These results are in contrast with those 

Among synthetic porphyrins, meso-tetraphenylporphyrin [H2(TPP)] is the most easily accessible porphyrin. 

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