Alfonso González-Ortega

Competitive Silyl–Prins Cyclization versus Tandem Sakurai–Prins Cyclization: An Interesting Substitution Effect

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.

Synthesis of silylated β-enaminones and applications to the synthesis of silyl heterocycles

Abstract Silyl β-enaminones have been synthesized by reductive cleavage of silylisoxazoles. These versatile synthons bearing the silyl group in different positions of the enamino ketonic system are of great interest in the construction of a variety of penta- and hexaheterocycles, which, in general, retain the silyl group attached at the ring or in a side chain.

Synthesis of Azepane Derivatives by Silyl-aza-Prins Cyclization of Allylsilyl Amines: Influence of the Catalyst in the Outcome of the Reaction

The synthesis of seven-membered nitrogen heterocycles by silyl-aza-Prins cyclization is described. The process provides trans-azepanes in high yields and good to excellent diastereoselectivities. Moreover, the reaction outcome is dependent on the Lewis acid employed. Thus, while azepanes are selectively obtained when InCl3 is used, the reaction in the presence of TMSOTf provides tetrahydropyran derivatives corresponding to a tandem Sakurai-Prins cyclization.

Efficient access to polysubstituted tetrahydrofurans by electrophilic cyclization of vinylsilyl alcohols

Vinylsilyl alcohols undergo intramolecular cyclization to provide di-, tri- or tetrasubstituted-tetrahydrofurans. The influence of the number and position of substituents in the stereoselectivity of the process has been studied. Moreover, DFT calculations have been performed to get better insight into the influence of the substitution pattern of the vinylsilyl alcohol in the stereoselectivity of the cyclization.

β-Aminoenones in the regioselective synthesis of 1,3,5-trialkylpyrazoles. The influence of the substituents in the mechanism and the regioselectivity of the reaction

β-Aminoenones react with monoalkyl hydrazines to give regioselectively 1,3,5-trisubstituted pyrazoles. The mechanism and level of regioselectivity depend on both the substitution pattern of the substrates and the reaction conditions. When the least bulky substituent is attached at the β-position of the enone, a high regioselectivity is obtained, usually higher than that from equivalent β-diketones. If the β-substituent is the bulkiest group, the regioselectivity decreases. Nevertheless, in the conditions reported in this paper, it is possible to prepare pyrazoles not obtainable from β-diketones.