Acid/base‐catalyzed cyclization of O‐alkynylphenylphosphonic acid monoesters and (O‐hydroxyphenyl)ethynylphosphinates

In this work, we found that acids (i.e., HCl and NaHSO3) rather than bases could catalyze the cyclization of o-alkynylphenylphosphonic acid monoesters at slow rates and give phosphaisocoumarins in low to medium yields, whereas the cyclization of (o-hydroxyphenyl)ethynylphosphinates proceeded very smoothly under basic conditions rather than acidic conditions, and a series of phosphachromones could be prepared in excellent yields at room temperature using K2CO3 as catalyst. This is the first example of the synthesis of phosphorus heterocycles via acid/base-catalyzed intramolecular cyclization of alkynes. Possible mechanisms were discussed. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:649–652, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20728