Preparation of benzannulated spiroketals by gold(III) catalyzed spirocyclization of alkynyl diols

Abstract

The first gold(III)-oxazoline catalysed intramolecular tandem dihydroalkoxylations of alkynyl diols to give benzannulated 5,6-spiroketal products is reported. The results showed that Au(III)-bisoxazoline (BOX) and Au(III)-pyridine-oxazoline complexes are highly efficient catalysts for such spirocyclizations. The mono- and dibenzannulated 5,6-spiroketals were obtained in high yields (> 90 %) by rapid conversion of symmetrical and nonsymmetrical alkynyl diols, respectively. The Au(III)-BOX-BF4 catalyst generated minor spirocyclization enantioselectivity (up to 6 % ee). The choice of solvent was important for the outcome of the reactions.