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Abstract
Loline (1) is a small alkaloid that, in spite of its simple-looking structure, has posed surprising challenges to synthetic chemists. It has been known for more than a century and has been the subject of extensive biological investigations, but only two total syntheses have been achieved to date. Here, we report an asymmetric total synthesis of loline that, with less then ten steps, is remarkably short. Our synthesis incorporates a Sharpless epoxidation, a Grubbs olefin metathesis and an unprecedented transannular aminobromination, which converts an eight-membered cyclic carbamate into a bromopyrrolizidine. The synthesis is marked by a high degree of chemo- and stereoselectivity and gives access to several members of the loline alkaloid family. It delivers sufficient material to support a programme aimed at studying the complex interactions between plants, fungi, insects and bacteria brokered by loline alkaloids. Loline is a small alkaloid with a deceptively simple-looking structure. Here, a remarkably short synthesis is reported, the key step of which is a transannular aminobromination. The synthesis provides access to loline and to several other members of the loline family in sufficient yield to support a programme investigating the complex biological interactions of these compounds. Cite this article
Cakmak, M., Mayer, P. & Trauner, D. An efficient synthesis of loline alkaloids. Nature Chem 3, 543–545 (2011). https://doi.org/10.1038/nchem.1072 