A new synthesis of (+)-dicrotaline (1), an 11-membered dilactonic pyrrolizidine alkaloid of retronecine (6) type has been achieved in one step by utilizing a tinmediated lactonization process.
Total synthesis of optically active integerrimine, a twelve-membered dilactonic pyrrolizidine alkaloid of retronecine type. III. Regioselective elaboration of the unsymmetrical twelve-membered dilactone and total synthesis of (-)-integerrimine