Octaethyl-1,3-oxazinochlorin: A β‑Octaethylchlorin Analogue Made by Pyrrole Expansion

Treatment
of the oxime of octaethyloxochlorin 4, available
from octaethylporphyrin 3, under Beckmann conditions
provided not the expected lactam, but octaethyl-1,3-oxazinochlorin 8, in which a pyrrole moiety of the parent oxochlorin was
expanded by an oxygen atom to an 1,3-oxazinone moiety. Its mechanism
of formation was demonstrated to occur along an “abnormal Beckmann”
pathway, followed by intramolecular ring closure and hydrolysis. The
work expands the methodologies known to convert octaethylporphyrin
to pyrrole-modified porphyrin analogues.