Two different mechanism pathways are observed for the reaction of allylsilyl alcohols 1 and aldehydes in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf). In the case of allylsilyl alcohols without allylic substituents, the reaction gives dioxaspirodecanes, which are the products of a tandem Sakurai-Prins cyclization. In contrast, allylsilyl alcohols with an allylic substituent (R(2)≠H) selectively provide oxepanes, thus corresponding to a direct silyl-Prins cyclization. Both types of product are obtained with excellent stereoselectivity. Theoretical studies have been performed to obtain some rationalization for the observed stereoselectivity.
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Departamento de Química Orgánica, Facultad de Ciencias , Campus Miguel Delibes, 47011 Valladolid, Spain.
A versatile method for the synthesis of dioxaspiroundecanes through a tandem Sakurai-Prins cyclization of allylsilyl alcohols in the presence of TMSOTf is described. The process is general and highly stereoselective with total control in the creation of three new stereogenic centers in a single step. Moreover, a very interesting chemoselectivity has been observed depending on the nature of the catalyst used or the substitution of the trishomoallylic alcohol, since the same reaction under BF3·OEt2 catalysis or using alcohols with allylic substituents provides exclusively the corresponding oxocanes, by a direct silyl-Prins cyclization.
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Department of Organic Chemistry, University of Valladolid, Campus Miguel Delibes, 47011 Valladolid (Spain), Fax: (+34) 983423013.
Two different mechanism pathways are observed for the reaction of allylsilyl alcohols 1 and aldehydes in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf). In the case of allylsilyl alcohols without allylic substituents, the reaction gives dioxaspirodecanes, which are the products of a tandem Sakurai-Prins cyclization. In contrast, allylsilyl alcohols with an allylic substituent (R(2)≠H) selectively provide oxepanes, thus corresponding to a direct silyl-Prins cyclization.
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Departamento de Química Orgánica, Facultad de Ciencias, Campus Miguel Delibes , 47011 Valladolid, Spain.
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