Total Synthesis of the Biphenomycins; V.¹ Synthesis of Biphenomycin A

The total synthesis of biphenomycin A is described. Two of the five stereogenic centres were formed by enantioselective hydrogenation of the corresponding didehydroamino acids using the rhodium-DIPAMP catalyst and the two stereogenic centres of the α-amino-β-hydroxy unit were created by enantioselective hydrogenation using the ruthenium-BINAP catalyst or via a stereoselective aldol condensation, respectively. The biphenyl structural element was constructed by a palladium(0)-catalyzed coupling reaction. The 15-membered ansa ring was closed in 85 % yield by use of the appropriate, linear pentafluorophenyl ester in the two phase system chloroform/aqueous sodium hydrogen carbonate.