Stereoselective synthesis of the butyrolactone and the oxazoline/furan fragment of leupyrrin A(1).

Stereoselective syntheses of the Northern and the Southern fragments 2 and 3 of leupyrrin A1 are reported. The convergent preparation of 2 is highlighted by a zirconocene-mediated one-pot cyclization-regioselective opening of an advanced diyne while the route to 3 involves a Krische allylation and a one-pot Sharpless dihydroxylation-cyclization. Comparison of the spectroscopic data with those reported for the natural product supports a relative stereochemical assignment within these heterocycles.