An Oxidative Dearomatization-Induced [5+2] Cascade Enabling the Syntheses of alpha-Cedrene, alpha-Pipitzol, and sec-Cedrenol

作者：Green Jason C; Pettus Thomas R R^*

来源：Journal of the American Chemical Society, 2011, 133(5): 1603-1608.

DOI：10.1021/ja109925g

Efficient syntheses of alpha-cedrene (1), alpha-pipitzol (2), and sec-cedrenol (3) were carried out using a new method, which was inspired by the proposed biosynthesis of the tricyclic skeleton of cedrol (12). The key transformation begins with the oxidative dearomatization of curcuphenol (5a) followed by an intramolecular [5 + 2] cycloaddition of the respective phenoxonium intermediate across the tethered olefin. The benzylic stereocenter effectively guides the formation of the first two stereocenters during the [5 + 2] reaction. The cascade then terminates with the selective incorporation of acetic acid to generate a third stereocenter, setting it apart from other previous cationic [5 + 2] reactions. The phenolic precursors (5a - h) are constructed from readily available salicylaldehydes, either as the racemate (one pot) or as a specific enantiomer (four pots) by a modification to our method for the generation of ortho-quinone methides (o-QMs).

• 出版日期2011-2-9