Total Synthesis of Calystegine B4

The total synthesis of calystegine B-4 was achieved in 10 steps from (-)-D-lyxose by using a new synthetic strategy to obtain the requisite protected hydroxylated 4-aminocyclohept-2-en-1-one without the problem of regioisomer formation that was a problem in the earlier synthesis of this natural product. The key steps included a Petasis-borono-Mannich reaction and a ring-closing metathesis reaction.