Base Induced Chiral Substituted Furans and Imidazoles from Carbohydrate-Derived 2‑Haloenones

Chiral
substituted furans and imidazoles are key intermediates
to access biologically important molecules. We describe herein a catalyst/ligand
free cascade Michael-type addition/intramolecular cyclization/carbohydrate-ring
opening of 2-haloenones with 1,3-dicarbonyl compounds or amidines
utilizing K2CO3/DMSO at ambient temperature
that provides a straightforward approach to a variety of optically
active (poly)­hydroxy furans and imidazoles containing multiple stereocenters
with good yield and excellent regioselectivity. The furan intermediates
provide efficient access to synthetically valuable substituted α-benzyloxyvinyl
ketones. The NMR spectrum of the substituted 2-methylfurans shows
an unusual long-range (5JH–H) 1H–1H COSY cross-peak between C2–CH3 and C4–H signals.