LiBF4-catalyzed formation of fused pyrano- and furanobenzopyrans
摘要:
Lithium tetrafluoroborate efficiently catalyzes an unusual cyclization of o-hydroxybenzaldimines with 2,3-dihydrofuran and 3,4-dihydro-2H-pyran at ambient temperature to afford a class of new pyrano- and furanobenzopyran derivatives in excellent yields with high diastereo selectivity. (C) 2001 Elsevier Science Ltd. All rights reserved.
Catalytic Asymmetric Inverse-Electron-Demand (IED) [4+2] Cycloaddition of Salicylaldimines: Preparation of Optically Active 4-Aminobenzopyran Derivatives
The catalyticasymmetricinverse-electron-demand (IED) [4+2] cycloaddition of various salicylaldehyde-derived N-arylimines with electron-rich alkenes in the presence of chiral BINOL-derived phosphoric acid catalysts has been studied with the aim of obtaining opticallyactive4-aminobenzopyranderivatives. Dienophiles such as 2,3-dihydro-2H-furan, benzyl N-vinylcarbamate and 2-vinylindole have been
Tritylium cation catalyzed interrupted Povarov reactions afforded cis-4-aminobenzodihydropyrans in excellent yields (90%) within 10 min by lowcatalystloading (1 mol %). Lewis acidic catalysis mechanism by carbocation was proposed and validated. Switching a one-pot batch version of the reaction into a two-stage convergent continuous flow procedures received 10-fold time reduction to 1 min with 88%
Bi(OTf)<sub>3</sub>-[Bmim]PF<sub>6</sub>: A novel and Recyclable Catalytic System for the Diasteroselective Synthesis of Cis-fused Pyrano and Furanobenzopyrans
作者:J. S. Yadav、B. V. S. Reddy、P. Narayana Reddy
DOI:10.1246/cl.2004.1436
日期:2004.11
The Stereoselective one-pot synthesis of cis-fused pyrano and furanobenzopyrans has been developed from o-hydroxybenzaldehydes, aromatic amines, and cyclic enol ethers in the presence of Bi(OTf) 3 in air- and moisture-stable ionic liquid, [bmim]PF 6 under mild conditions. The recovered ionic liquid containing Bi(OTf) 3 can be reused three to five subsequent runs with only a gradual decrease in activity