Access to Enantiopure 2,5-Diaryltetrahydrofurans - Application to the Synthesis of (-)-Virgatusin and (+)-Urinaligran

The diastereoselective Mn-III-promoted radical addition of beta-oxoesters 1 onto N-cinnamoyloxazolidinones 2 afforded 2,3-dihydrofurans 3. After catalytic hydrogenation of the C=C bond, followed by reductive removal of the chiral auxiliary, the resulting enantiopure tetrahydrofurans 5 were trans-formed in two steps into naturally occurring (-)-virgatusin and (+)-urinaligran and two other, nonnatural, tetrasubstituted THF lignans. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)