Novel synthesis of naphtho[2,1-b]pyrano pyrrolizidines and indolizidines through intramolecular 1,3-dipolar cycloaddition reaction

A facile synthesis of a series of naphtho[2,1-b]pyrano pyrrolizidines and indolizidines was accomplished in good yields in a one-pot reaction through intramolecular 1,3-dipolar cycloaddition of azomethine ylides with Baylis-Hillman adducts as dipolarophiles. The protocol is applicable to a wide variety of photochromic and biologically active napthopyrano products. The regio and stereochemical outcome of the cycloaddition reaction was ascertained by X-ray crystallographic study of some of the products.