Chiral silanes are versatile intermediates for stereoselective transformations in organic synthesis. [1] Transition-metal-catalyzed carbenoid insertion into SiรH bonds provides a direct and efficient method for the synthesis of silane-containing compounds. [2] The most popular catalysts used in SiรH bondinsertion reactions have been copper(I) and rhodium(II) complexes. [3] In 1996, Doyle and Moody [4] reported the first asymmetric Si ร H bond-insertion reaction of a-diazophenylacetates, catalyzed by a chiral dirhodium(II) carboxylate and carboxamidate complexes with moderate enantioselectivities (up to 47 % ee). A year later, Davies and co-workers [5] achieved high enantioselectivities (up to 95 % ee) in the Si ร H bond insertion of a-vinyldiazoacetates catalyzed by rhodium(II)
N-[p-(dodecylphenyl)-sulfonyl]prolinate. Recently, Ge and Corey [6] reported a Si ร H bond insertion of an a-diazoketone with a N-nonafluorobutanesulfonylproline rhodium(II) catalyst to prepare 6-silyl-2-cyclohexenones with 94 % ee. Several other chiral rhodium(II) catalysts have also been used in the Si ร H bond-insertion reaction with different diazo compounds, with no marked improvement in enantiocontrol. [7] Although copper catalysts had been applied to SiรH bond-insertion reactions before rhodium catalysts, [3] the copper-catalyzed asymmetric SiรH bond insertion has not been widely exploited. The only example of a coppercatalyzed asymmetric Si ร H bond-insertion reaction was reported by Panek and Jacobsen. [8] Using a copper chiral-Schiff-base complex as a catalyst, they obtained SiรH bondinsertion products in high yields with up to 88 % ee, for the reaction of a-diazophenylacetate with trialkylsilanes. In previous studies, we accomplished highly enantioselective insertions of a-diazoesters into N ร H bonds of anilines [9] and O ร H [10] bonds of phenols and water, using copper complexes of chiral spiro-bisoxazoline ligands 1 (spirobox; Scheme 1). We report herein a copper/chiral spiro-diimine-complexcatalyzed asymmetric carbenoid insertion into the SiรH bond, with high yields and excellent enantioselectivities (up to 99 % ee).
was determined by chiral HPLC analysis using a Daicel Chiralcel OD-H column.