Alternative Asymmetric Synthesis of Two Venom Alkaloids of Ants Leptothoracini (Myrmicinae)

An alternative asymmetric synthesis of ant venom alkaloids (R)-Leptothoracine 1 and (R)-3-methyl-N-(2-phenylethyl)pyrrolidine 2 are described. The synthesis was achieved by replacement of the hydroxyl group of dimethyl (2S, 3R)-3-methylmalate 7 with chloride, followed by radical dechlorination and ester reduction, which afforded (R)-2-methyl-1,4-butanediol 10 in 79.7 % ee. Diol 10 was further transformed into the natural enantiomer of ant venom alkaloids (R)-Leptothoracine 1 and 2 by usual bis-tosylation and amination procedures.