Abstract
A series of novel isoxazolo analogues 11 of the dibenzazonine alkaloid protostephanine (1) has been prepared. A new regiospecific and potentially general aza macrocyclic ring forming process was developed where the first step was the 1,3-dipolar cycloaddition of benzonitrile oxide to the readily available examine 6. The product, isoxazoline 9a, under solvolytic conditions that normally convert monocyclic 5-aminoisoxazolines to isoxazoles failed to give the desired aza macrocycle 14. Alternate sequences involving quaternization of 9a with methyl iodide followed by either solvolysis in polar solvents or base-induced elimination were successful and gave the target structure 11a in excellent overall yield. X-ray crystallographic analysis of the quaternized intermediate 10a corroborated the assignment of structure and defined the crystal-state conformation
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