Catalytic aza-Wittig Cyclization

Significance

The authors report examples of phenanthridine 1 and benzoxazole 2 synthesis by iminophosphorane generation followed by intramolecular aza-Wittig cyclization catalyzed by commercially available phospholene oxide 3. Both azine and azole heterocycles have been synthesized in moderate to good yields (30-87%yield) with attractively low catalyst loadings down to 1 mol%. Furthermore, the use of carboxylic acid derived isocyanates offers a novel disconnection for the synthesis of (benz)oxazoles.