Regioselective lithiations of a pterocarpan skeleton: the first synthesis of (±)-4′-dehydroxycabenegrin A-I

Maackiain O-MOM derivative 3b was regioselectively lithiated at the C-10 position of D-ring and reacted with electrophiles. Regioselective lithiation of the C-10 TMS-substituted derivative 5d, followed by organocopper formation and treatment with prenyl bromide, enabled the desired prenylation at C-4. The obtained compound 6d was employed in the first synthesis of racemic 4′-dehydroxycabenegrin A-I, 4. Moreover, dialkylation of 3b at the two most reactive sites could be effected through the generation of a dilithiated species. A preliminary result dealing with diethylcarbamate derivative 3c is also shown.