Sequential Hiyama Coupling/Narasaka Acylation Reaction of (E)-1,2-Disilylethene: Rapid Assembly of α,β-Unsaturated Carbonyl Motifs

The synthesis and application of (E)-1,2-disilylethene 5 as a central functional building block in a sequential Hiyama coupling/Narasaka acylation reaction are described. Its use in the rapid and versatile construction of a,p-unsaturated carbonyl motifs found in a number of polyunsaturated natural products has been demonstrated. It was observed that due to the differential intrinsic reactivity of the two carbon-silicon bonds, this bis-metallated lynchpin-type reagent is activated selectively and sequentially by Pd and Rh catalysis, negating the need for any protecting group. A number of (E)-alpha,beta-unsaturated ketones were efficiently synthesized with complete chemoselectively in the presence of a variety of halides and anhydride acids. Conjugated polyunsaturated ketones and diversely alpha'-functionalized alpha,beta-enones, such as chalcones, a heterocyclic dienone and the highly conjugated ethyl (2Z,4E)-6-oxo-6-(2-thienyl)hexa-2,4-dienoate, were obtained in good overall yields. Thus, this coupling sequence provides a high degree of modularity, that is, a single template is likely to produce a large number of synthetic targets. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)