Tandem Allene Formation/Intramolecular Cyclization of Phosphorus‐Substituted Propargylic Alcohols and Substituted Phenols to Access C4‐Phosphorylated 2 H ‐Chromenes

ABSTRACT In this study, we demonstrated that phosphorus‐substituted propargylic alcohols could undergo tandem allene formation/intramolecular cyclization to afford phosphorylated heterocycles. In the presence of 5 mol% of In(ClO 4 ) 3 ·8H 2 O or Hg(ClO 4 ) 2 ·3H 2 O, the reaction between phosphorus‐substituted propargylic alcohols and substituted phenols proceeded via a tandem regioselective SN1’ substitution/intramolecular 6‐ endo ‐trig cyclization, which served as an alternative procedure for the preparation of C4‐phosphorylated 2 H ‐chromenes under mild conditions (air, 40°C or 60°C, 0.5–24 h). The richer diversity of substituents and their positions on the aryl ring of 2 H ‐chromenes and its tolerance to P(O)(OR) 2 groups make this protocol as a good supplement to previous report. The synthetic utilities were illustrated by the scaled synthesis and further elaboration of the obtained products to polycyclic compounds bearing phosphoryl groups, 2 H ‐chromene and five or six‐membered O ‐heterocycles. Control experiments further confirmed the tandem allene formation/intramolecular cyclization sequence.