Study On The Nazarov Reaction Of α-Alkenoyl Ketene Dithioacetals

The Nazarov cyclization, a powerful tool for the construction of five-membered carbocycles from divinyl ketones and related compounds, has attracted increasing attention in recent years due to its wide applications in the synthesis of complex natural and unnatural products. Generally, either a protic acid or strong Lewis acid(e.g., BF3, SnCl4, TiCl4, or AlCl3) is required to promote Nazarov cyclization, and one or more molar equivalents of Lewis acid is necessary for the best results. Recently, more effective promoters, including transition metal catalysts and nonmetal initiators, have been developed both to improve the efficiency of the reaction and to expand the synthetic scopes of the process in the evolution of the Nazarov cyclization as a versatile synthetic methodology.Among the variousα-oxo ketene dithioacetals,α-alkenoyl ketene dithioacetals are easier to prepare and bear much more functionalities. From the view of structure,α-alkenoyl ketene dithioacetals contain divinyl ketones.In addition, the variations of the substituents atα′-position and the alkylthio groups have the significant effect on their reactivity. Therefore, studies on the synthesis and the applications ofα-alkenoyl ketene dithioacetals should be a valuable research project.Based on our early work, we will discuss the coupling the Nazarov cyclization-halogenation reaction ofα-alkenoyl ketene dithioacetals under Vilsmeier conditions. A series of functionalized cyclopentadienes were be synthesized, which are developed to construct five-membered carbocycles derivatives. The following statements are the brief of my work.First, a series ofα-oxo ketene dithioacetals were preparated on the basis of our recent work.Second, we investigated the aldol reactions of the specialα-oxo ketene dithioacetals with aromatic aldehydes under the mild conditions in good yields.In the end, a Novel and facile method has been used to synthesize functionalized cyclopentadienes by Nazarov cyclization ofα-alkenoyl ketene dithioacetals under Vilsmeier conditions.Twenty-eight new compounds were synthesized and characterlized by IR, Mass and NMR (¹H, ¹³C) spectrum in this thesis.