Alkenyl silanes are attractive building blocks for various synthetic transformations in organic synthesis and material science. To access such important compounds, design and development of efficient catalytic systems for synthetic methods are highly in demand. Although transition metal-catalyzed alkyne hydrosilylation has been a useful tool, regioselective hydrosilylation of propargyl alcohols still remains challenging due to the instability of the oxasilacyclobutanes intermediates formed. This research is focused on developing a transition metal-catalyzed regio- and stereoselective intramolecular hydrosilylation of propargylic alcohols. Use of easily accessible, inexpensive, and readily installable hydrosilyl acetal as a directing group achieves high reactivity as well as high regio- and stereoselectivity. Specifically, current strategy involves iridium-catalyzed hydrosilylation of progargyl ester, followed by rhodium-catalyzed intramolecular alkyne hydrosilylation through a 6-exo-syn cyclization. This method successfully produced a range of cyclic α-(E)-vinylsilanes (i.e., dioxasilinanes) in moderate to excellent yields (12 examples; only one regioisomer) and showed good functional group tolerance. Steric and electronic impacts of hydrosilyl acetals on the cyclization in terms of reactivity and regioselectivity to generate cyclic α-(E)-vinylsilanes (6 examples; only one regioisomer) are studied. The versatility of this strategy is demonstrated in a complex molecular setting with substituted-ethynylesterdiol, which is converted to the corresponding dioxasilinane. This protocol provides a new route to access α-(E)-vinylsilanes.

Hydrosilyl acetal-directed catalytic exo-syn hydrosilylation of propargylic alcohols

2019 Spring National Meeting

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