A dirhodium(II)-carbenoid route to (-)- and (+)-Geissman-Waiss lactone: synthesis of (1R,7R,8R)-(-)-turneforcidine.

(-)- and (+)-Geissman-Waiss lactone, 4b, was efficiently prepared via the intramolecular C-H insertion reaction of the chiral nonracemic diazoacetates (-)-5a and (+)-5b catalyzed by dirhodium(II) tetrakis[methyl (5R and 5S)-3-phenylpropanoyl-2-imidazolidinone-5-carboxylate]. The cyclization was found to proceed with excellent regioselectivity and cis-diastereoselectivity. The bicyclic lactone (-)-4b was successfully used in the synthesis of the necine base, (-)-turneforcidine 2.