A new procedure for highly stereoselective and regioselective synthesis of 2-ethynyl-3-hydroxytetrahydropyran derivatives based on alkyne-Co 2 (CO) 6 complex
Treatment of trans-epoxides 3 with Co2 (CO) 8 gave the corresponding cobalt complexes, which were subsequently exposed to a catalytic amount of BF3· OEt2 at− 78° C to provide exclusively cis-2-ethynyl-3-hydroxytetrahydropyran derivatives via endo mode cyclization pathway. cis-Congeners, cis-3 afforded the corresponding trans tetrahydropyran derivatives exclusively. This novel cyclization has been found to proceed with retention of ...