Stereoselective reductive opening of 2,3-benzofuran - A two-step synthesisof 2H-chromenes including deoxycordiachromene

The reaction of 2,3-benzofuran (1) with lithium and a catalytic amount of 4 ,4 ' -di-tert-butylbiphenyl (TDBB, 5 mol %) in THF at 0 degreesC leads to t he stereoselective ring opening of the heterocycle, yielding the (Z)-organo lithium derivatives (2) which, by reaction with different electrophiles [H2 O, D2O, tBuCHO, PhCHO, Ph(CH2)(2)CHO, Me2CO, nPrCOMe, PhCOMe, (CH2)(4)CO] a t -78 degreesC and final hydrolysis with water, give the expected (Z)-produ cts 3. Cyclisation of the products obtained by reaction with carbonyl compo unds under acidic conditions affords the expected substituted 2H-chromenes 4, including deoxycordiachromene 4j.