Enantiospecific Total Synthesis of (-)-Hyacinthacine A1 and (+)-Hyacinthacine A1 and Their Homologues Using Nitrogen Substituted Donor-Acceptor Cyclopropane

A concise and efficient enantiospecific total synthesis of (-)-hyacinthacine A(1) and (+)-hyacinthacine A(1) was achieved from commercially available starting material L-pyroglutamic acid and D-glutamic acid, respectively. For the synthesis of this trihydroxylated pyrrolizidine ring, we employed the nitrogen-substituted donor-acceptor cyclopropane as a key intermediate. The synthetic approach relies on two crucial steps, highly stereo- and regioselective intramolecular cyclopropanation with Rh-2(OAc)(4) and regioselective ring opening of a nitrogen-substituted donor-acceptor cyclopropane.