Electron‐rich aza‐aromatic compounds such as indoles and pyrroles are structures of particular interest and importance in organic chemistry. A useful methodology for the regioselective introduction of the sulfenyl group into electron‐rich aza‐aromatics using S‐alkyl‐ and S‐arylthiophthalimides as sulfenylating agents is described. Catalytic amounts of CeCl3·7H2O/NaI are crucial to the promotion of this regioselective carbon–sulfur‐bond‐forming electrophilic aromatic substitution reaction. The reaction occurred under mild conditions, and the products were obtained in good to excellent yields. The method represents an efficient preparation of sulfenyl aza‐aromatics, which are useful intermediates for important organic transformations, due to the great importance of functionalized indoles among natural compounds and pharmaceutical products.
Functionalized polysubstituted oxazoles are an important class of five‐membered N,O‐heterocycles that occur widely in the structure of natural products and fine chemicals. They are also often used as building blocks in the synthesis ofheterocyclic molecules with more complex structures. Therefore, efficient synthetic protocols based on Lewis acid promoted reactions are desirable. In this context, we report that, under microwave irradiation, the CeCl3·7H2O/NaI/I2 system is capable of promoting a 5‐exo‐dig cyclization of propargyl amides with good functional group tolerance. The microwave reactor also provides a more convenient and safer method for heating the reaction. This methodology represents a straightforward CeCl3·7H2O/NaI/I2 promoted cyclization using microwave irradiation to accomplish the synthesis of polysubstituted oxazole derivatives.
Lewis acid promoted elimination of p-toluenesulfinc acid from sulfonyl indazoles and sulfonyl indoles generates the corresponding iminium ion that reacts with allyltin reagents, silyl enol ethers, silyl ketene acetals and electron-rich aromatics leading to functionalized indazole and indole derivatives.
A new procedure for the sulfenylation of indoles and pyrroles based on an aromatic substitution with α‐acylthiones used as electrophiles is described. The sulfenylating species were obtained, under very mild reaction conditions, from N‐thiophthalimides, using a weak base (pyridine or triethylamine) as promoter. The overall yields obtained are comparable with those obtained by other known sulfenylation protocols, which typically require harsher reaction conditions and/or metal‐containing Lewis acids as promoters.
A Base-Mediated Mild Sulfenylation of Indoles and Pyrrole with -Acylthiones.-Indole derivatives react with 1 equiv. of o-thioquinone derived from (II) or dioxothione [cf. (XI)] in the presence of 1 equiv. of NEt 3 to produce the desired products including the 2-substituted gramine derivative (V). The yields are comparable with those obtained by known protocols (harsh conditions, metal-containing Lewis acids). The analogous procedure with pyrrole requires an excess of (XIII) in order to avoid formation of by-products. -(VIGLIANISI, C.; MARCANTONI, E.; CARAPACCHI, V.; MENICHETTI*, S.; MARSILI, L.; Eur. J. Org. Chem. 2014, 29, 6405-6410, http://dx.
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