Eight-step total synthesis of (+)-crambescin A

(+)-Crambescin A belongs to the polycyclic guanidine natural product family and has been shown to possess various medically important properties. The chiral bicyclic guanidine structure of (+)-crambescin A presents a challenge for chemical synthesis. Here we implement a novel asymmetric Biginelli reaction strategy to achieve the enantiospecific total synthesis of (+)-crambescin A in only 8 steps from the abundant and inexpensive aliphatic aldehyde, urea and methyl 3-oxobutanoate.