[4+1] Annulation Reactions Of Stable Sulfur Ylides In The Synthesis Of Heterocycles

Heterocycles are extraordinarily significant compounds, making up more than half of the known organic compounds. They have been frequently recognized as a pivotal structural component in natural products and agrochemicals as well as pharmacological agents of various therapeutic actions, displaying a range of versatile biological activities. Also, some of the heterocycles have important applications in materials science, supramolecular, polymer chemistry and organic conductors, etc. Heterocycles are also of substantial interest due to their extensive synthetic utility as synthetic intermediates, protecting groups, chiral auxiliaries, organocatalysts, and ligands in asymmetric metal catalysis in organic synthesis. Therefore, considerable attention has been drawn to develop efficient and green strategies to synthesize heterocycles.Based on the property of sulfur ylides and photocatalysis in cascade reactions, in the present dissertation, four kinds of heterocycles were obtained with high reaction efficiency. The abstracts for each one were listed as follows:1、An unprecedented protocol for the synthesis of indoles, which involves cascade reaction ([4+1] annulation/Elcb elimination) of sulfur ylides and N-(ortho-chloromethyl)aryl amides, has been developed. The reaction features a simple procedure and mild conditions, and it represents a new strategy for the direct and efficient synthesis of structurally diverse indoles. Importantly, sulfonium salts, the precursors of sulfur ylides, were also found to be applicable to the one-pot procedure for the synthesis of selected compounds, thus simplifying the procedure further. In general, this method has a broad application prospects.2、Based on the previous work and mechanism insight, we controlled the amount of base to avoid the Elcb elimination process and reported a successful implemention of this strategy for the facile construction of 2-substituted indolines from [4+1] annulation of sulfur ylides and N-(ortho-chloromethyl)aryl amides. The described strategy, taking advantage of chiral sulfur ylides derived from (R)-BINOL, represents a direct procedure to access chiral 2-substituted indolines in with moderate to high yields and enatioselectivity (70-93% yields, up to 95.5:4.5 e.r.). Importantly, after the completion of the reaction, chiral sulfide can be recovered in 95% yield and reused for the synthesis of chiral sulfur ylide. Finally, the absolute configuration of cycloadduct indoline was unambiguously confirmed to be R by X-ray diffraction analysis. And a possible model for asymmetric induction was proposed.3、We also applied the above [4+1] annulation protocol to construct 2-substituted dihydrobenzofurans. An asymmetric annulation of stabilized sulfur ylides with in situ-generated ortho-quinone methides using the C2-symmetric urea catalyst via multiple hydrogen-bonding activation to allow an access to enantioselective 2-substituted-2,3-dihydrobenzofurans has been described (up to 98% yield and 78% ee). Based on our previous work about organocatalytic reactions of sulfur ylide, we proposed a possible active mode for the process.4、Photocatalysis enables the cascade reactions of indoles and CBr4 in MeOH through C(sp2)-H functionalization/methanolysis sequence. The title reaction provides an efficient access to indole 2-and 3-carboxylates in a single operation (no pre-installation of protecting-as well as directing-groups was required) with good yields under mild reaction conditions. We got insight to the mechanism based on the studies including absorption spectra, quenching experiments, on-off Switching of the light, etc.