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Stereoselective Synthesis of Natural Products Promoted by Titanocene(III)

Abstract:

The use of radical reactions in organic synthesis is increasing every year. Bis(cyclopentadienil)titanium(III) chloride [Cp2TiCl] promotes and catalyzes several transformations under mild conditions compatible with several functional groups. Due to its power as a mild single-electron transfer reagent, Cp2TiCl has become a formidable tool in organic synthesis. Thus, this catalyst is being increasingly used in the synthesis of complex multifunctional molecules, mainly natural products and related compound useful in pharmacology. This chapter will include a comprehensive review of those works on Cp2TiCl-mediated synthesis of natural products published from 2006 onward, as there is a previous comprehensive review covering the subject until 2005. The biosynthetic origin of the natural products here reported has been chosen as the method to classify those molecules for which a synthesis is presented. Terpenoids constitute the class of natural products with more examples in this field (Rosales et al., 2015; Morcillo et al., 2014; Rosales et al., 2015; Fernández-Mateos et al., 2011; Nugent et al., 1988; RajanBabu et al., 1989; RajanBabu et al., 1990; RajanBabu et al., 1994; Justicia et al., 2009; Jiménez et al., 2010) [2–8] followed by polyketides (Fernández-Mateos et al., 2013; Lee et al., 1992; Dixit et al., 2007; Mori et al., 1997; Yadav et al., 2005; Mandal et al., 2010; Gansäuer et al., 2009) [9–12] and phenylpropanoids (García Santos et al., 2015; Barrero et al., 2001) [13,14]. Moreover, some nitrogen-containing substances have also been prepared by titanocene(III)-based methods, especially antibiotics and alkaloids (Bermejo et al., 2006; Pérez Morales et al., 2013) [15,16]. Finally, new methodologies applying Cp2TiCl catalysis, which can potentially lead to complex natural products, are also shown (Gianino et al., 2014) [106d].