Mixing readily available alkynes, pyrroles, and triethylsilane along with an indium catalyst was found to be an efficient procedure to introduce alkyl groups onto a beta-position of pyrroles in a complete regioselective manner. This is the first demonstration of catalytic beta-alkylation of pyrroles in a single step.
Silver and zinc salts were found to efficiently catalyze the addition of an N-H bond of pyrazoles to alkynes. With silver triflate as a catalyst, two pyrazoles regioselectively attacked the same carbon atom of the CϵC bond of aliphatic terminal alkynes to give gem-dipyrazolylalkanes predominantly. Replacement of silver triflate with zinc triflate allows us to achieve double addition of pyrazoles to aromatic terminal alkynes. In contrast to the selective double addition, the corresponding single addition of aliphatic and aromatic terminal
A pyrrolyl group bound to an sp 3 carbon atom in gem-dipyrrolylalkanes was found to be successfully replaced by a certain range of carbon nucleophiles in the presence of an indium catalyst. The reaction can also be performed efficiently as a three-component assembly of alkynes, pyrroles, and car-
Pyrrole derivatives R 0120Indium-Catalyzed Reductive Alkylation of Pyrroles with Alkynes and Hydrosilanes: Selective Synthesis of β-Alkylpyrroles. -The reaction tolerates functional groups in the terminal alkyne. In some cases, premixing of pyrrole derivative, alkyne and In catalyst prior to the addition of silane is needed. The reaction cannot be applied directly to unprotected pyrrole; the target compound is prepared by deprotection of the N-Bn derivative. -(TSUCHIMOTO*, T.; WAGATSUMA, T.; AOKI, K.; SHIMOTORI, J.; Org. Lett. 11 (2009) 10, 2129-2132; Dep. Appl. Chem., Meiji Univ., Kawasaki 214, Japan; Eng.) -R. Steudel 41-102
Pyrazole derivatives R 0180Lewis Acid Catalyzed Addition of Pyrazoles to Alkynes: Selective Synthesis of Double and Single Addition Products. -The addition of pyrazole (I) to terminal and internal alkynes is efficiently catalyzed by silver or zinc salts. Double [cf. (III)] and single addition products [cf. (IV)/(V)] are selectively obtained depending on the salt used. The reactions are atom-economical and tolerate a wide range of functional groups. The reaction mechanisms are discussed in detail. -(TSUCHIMOTO*, T.; AOKI, K.; WAGATSUMA, T.; SUZUKI, Y.; Eur. J. Org. Chem. 2008, 23, 4035-4040; Dep. Appl. Chem., Meiji Univ., Kawasaki 214, Japan; Eng.) -Mischke 50-114
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