Total synthesis and determination of the absolute configuration of a natural analgesic: crotonine

We report the first total synthesis of four possible absolute configurations and four other regional isomers of a naturally occurring alkaloid crotonine, which was isolated from Croton tiglium L. (Euphoriaceae) without elucidation of its absolute configuration. The concise five-step route with a chirally poor and regioselective strategy starting from monosaccharides was established, and the absolute structure of the natural crotonine was determined by comparison of the NMR spectra and optical rotations of the synthetic products. [Image: see text] ELECTRONIC SUPPLEMENTARY MATERIAL: Supplementary material is available for this article at 10.1007/s13659-013-0080-1 and is accessible for authorized users.