A Catalyst‐Free Self‐Catalyzed [3+2] Cycloaddition Reaction of 3‐Isothiocyanato Oxindoles and Vinylpyridines

Abstract

A catalyst‐free self‐catalyzed [3+2] cycloaddition reaction of 3‐isothiocyanato oxindoles with vinylpyridines has been established, affording the desired products in high yields (up to 97 %) with moderate to good diastereoselectivities (up to 11:1) under mild conditions. The reaction mechanism has been investigated by control experiments, DFT calculations of pKa values and the kinetic studies, revealing that this reaction featured the mutual activation between 3‐isothiocyanato oxindole and vinylpyridine to generate the reactive species. Furthermore, these products could be easily transformed into the corresponding methylated and hydroxylated products under basic conditions.

A Catalyst‐Free Self‐Catalyzed [3+2] Cycloaddition Reaction of 3‐Isothiocyanato Oxindoles and Vinylpyridines

“…The configurations of 3aa, 3ai and the two diastereomers of 4aa have been unambiguously determined by X-ray diffraction and their ORTEP drawings are shown in Figure 1 (see Figures S1-S4 in the Supporting Information for more details). [14] To shed lights on the mechanistic insights of this reaction, several control experiments were conducted (Scheme 2). Firstly, we used styrene to react with 1a in toluene, but no reaction occurred even in the presence of 1.0 equiv.…”

Stereo‐ and Regioselective Construction of Spirooxindoles Having Continuous Spiral Rings via Asymmetric [3+2] Cyclization of 3‐Isothiocyanato Oxindoles with Thioaurone Derivatives

“…Then, we lowered the reaction temperature to 0°C (Table 1, entry 9) and -40°C (Table 1, entry 9) but no obvious influence was found on the reaction. Finally, a survey on the common solvents were taken (Table 1, entries [11][12][13] which indicated that DCM was the best solvent for the reaction, providing the desired product 3aa in 95 % yield along with 96 % ee and more than 20:1 dr value.…”

“…[11] Very recently, some studies on thioaurone derivatives indicated that thioaurone derivatives were active exocyclic olefins. [12] Inspired by the above successful reports together with our previous successes in preparing diverse spirooxindoles, [13] we envisaged that a predicted [3+2] annulation could occur between 3-isothiocyanato oxindoles and thioaurone derivatives to generate the spirooxindoles containing continuous spiral ring structures including an uncommon sulfur-containing spirocyclic ring (Scheme 1, this work).…”

One-pot catalyst-free synthesis of benzopyrroxazine derivatives by a mutually activated sequential annulation process

“…12 More relevantly, the pyridine moiety of vinyl pyridines can serve as a Lewis base catalyst. Therefore vinyl pyridines have been used in catalyst-free self-catalyzed annulation reactions, 13 which were reported by Shi's group (Scheme 1c). 14 A simple and effective non-catalytic reaction system is the long-term goal of the chemical industry.…”

“…Product 3af was obtained in 60% yield, lower than that of 3ae perhaps due to the weaker basicity of 2f . 13 Then electron-donating substituted 5-methyl-2-vinylpyridine 2g was examined under the standard conditions. However, no reaction occurred.…”