Bisnorditerpene

A bisnorditerpene dilactone from Podocarpus nagi. Kubo, I. Ying, B.P. Phytochemistry 1991,30,3476-3477. 

The first total synthesis of barbacenic acid, a bisnorditerpene containing five contiguous stereocenters, was achieved by A. Kanazawa et. al. They started out from a Wieland-Miescher ketone analogue that could be synthesized with high yield and excellent enantioselectivity by the procedure of S. Takahashi. According to this procedure, the Michael addition product 2-methyl-2-(3-oxo-pentyl)-cyclohexane-1,3-dione was cyclized in the presence of (S)-(-)-phenylalanine and D-camphorsulfonic acid. 

Patin, A., Kanazawa, A., Philouze, C., Greene, A. E., Muri, E., Barreiro, E., Costa, P. C. C. Highly Stereocontrolled Synthesis of Natural Barbacenic Acid, Novel Bisnorditerpene from Barbacenia flava. J. Org. Chem. 2003, 68, 3831-3837. 

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