Montmorillonite K-10 as a mild acid for the Nicholas reaction

The use of Montmorillonite K-10 as a convenient acid component in the Nicholas reaction is described. Its use permits functional selectivity, inter- and intramolecular reactions and convenience in the experimental conditions. A four-step one-pot [Co2(CO)6–acetylene complex formation, THP-removal, cyclization and complex cleavage] process permits the direct synthesis of 2-ethynyl-tetrahydrofuran from 6-(tetrahydro-2H-pyran-2-yloxy)hex-1-yn-3-ol.