Advanced Synthesis of Dihydrofurans: Effect of Formic Acid on the Mn(III)-Based Oxidation

Abstract

The Mn(III)-based oxidation of a tertiary alkylamine, such as nitrilotris(ethane-2,1-diyl) tris(3-oxobutanoate) (1) with 1,1-diphenylethene (2a), effectively proceeded in an acetic acid–formic acid mixed solvent to give nitrilotris(ethane-2,1-diyl) tris(2-methyl-5,5-diphenyl-4,5-dihydrofuran-3-carboxylate) (3). Other typical Mn(III)-based reactions of various β-diketo esters 4a–e, 2,4-pentanedione (6a), malonic acid (6b), and diethyl malonate (6c) with 1,1-diarylthenes 2a–d were also investigated in a similar acetic acid–formic acid mixed solvent and the reaction rate was accelerated and the product yield increased.

GRAPHICAL ABSTRACT

Keywords:

• Alkylamine
• 4,5-dihydrofurans
• formic acid
• manganese(III) acetate
• oxidation

SUPPLEMENTAL MATERIAL

Measurements, materials, IR, ¹H and ¹³C NMR spectra, distortionless enhancement by polarization transfer (DEPT), and fast atom bombardment (FAB) high-resolution mass spectrometry HRMS) data for known compounds 5ba, 5bb, 5bc, 5bd, 5da, and 7–10, and copies of ¹H and ¹³C NMR, FAB MS and IR spectral charts for all new compounds 3, 5aa, 5ca, and 5ea for this article can be accessed on the publisher’s website.