Zr-Catalyzed Carboalumination: A New Route to Tocotrienols

Vitamin E, consisting of the groups of tocotrienols 5 and tocopherols 6, is the biologically most important fat-soluble antioxidant. In the context of total synthesis of these compounds,^[1] the Zr-mediated carboalumination methodology^[2] was applied. Alkyne 3, easily available from (E)-geranylacetone (4), delivers (all-E)-alkenyl iodide 2 for the coupling with (enantiomerically pure) aldehydes 1 to various stereochemically defined homologous trienols 5, e.g. serving as starting materials for the highly stereoselective Ir-catalyzed asymmetric hydrogenation to tocopherols 6.^[3] [1] a) T. Netscher, Chimia 1996, 50, 563; T. Netscher, Vitamins and Hormones 2007, 76, 155; b) C. Rein, P. Demel, R.A. Outten, T. Netscher, B. Breit, Angew. Chem. Int. Ed. 2007, 46, 8670; c) T. Netscher, M. Scalone, R. Schmid in Asymmetric Catalysis on Industrial Scale, H.-U. Blaser, E. Schmidt (eds.), Wiley-VCH, Weinheim, Germany, 2004, p. 71. [2] a) E. Negishi, Pure Appl. Chem. 1981, 53, 2333; b) S. Huo, E. Negishi, Org. Lett. 2001, 3, 3253. [3] S. Bell, B. Wüstenberg, S. Kaiser, F. Menges, T. Netscher, A. Pfaltz, Science 2006, 311, 642.