Preparation of Intermediates for Fluorinated Lignans by Conjugated and Tandem Additions on 3-Fluorofuran-2(5H)-one

Abstract

Two syntheses of 3-fluorofuran-2(5H)-one (1) based on Wittig-Horner reaction of ethyl (diethoxyphosphoryl)fluoroacetate (15) with 2-oxoethyl acetate (16) or on transformation of D-erythronolactone (10) are given. 3-Fluorofuran-2(5H)-one (1) and ethyl 2-fluorobut- 2-enoate (2) undergo conjugate addition with soft nucleophiles based on arene- carboxaldehyde dithioacetals 7 to form 2-fluorolactones 3 and 2-fluoroalkanoates 4. Intermediate enolates can be trapped in the sense of tandem addition with arenecarboxaldehydes 8 or (arylmethyl)bromides 9 to form intermediates 5 and 6 for fluorolignans. Although the conjugate addition proceeds with low stereoselectivity yielding mixture of both diastereoisomers, the electrophile in tandem addition attacks the intermediary fluoroenolate exclusively anti to its bulky β-substituent in good accord with non-fluorinated furan- 2(5H)-ones.