Chiral Imidodiphosphoric Acid-Catalyzed Highly Diastereo- and Enantioselective Synthesis of Poly-Substituted 3,4-Dihydro-2H-pyrans: [4+2] Cycloadditions of β,γ-Unsaturated α-Ketoesters and 3-Vinylindoles

Imidodiphosphoric acids were employed to catalyze inverse-electron-demand hetero-Diels Alder reaction of beta,gamma-unsaturated alpha-ketoesters and 3-vinylindoles. A series of optically active 3,4-dihydro-2H-pyran derivatives with three contiguous stereogenic centers was synthesized in excellent yields (70-99%), diastereoselectivities (>20:1), and enantioselectivities (73-99%). The resulting indole containing 3,4-dihydro-2H-pyran could be converted to tetrahydropyran derivatives, which appear in several biological active compounds by simple hydrogenation reduction.