Indolylboron ate complexes readily generated from 2-lithioindoles and boronic esters underwent multicomponent dearomative coupling with D-A cyclopropanes and alkyl halides in the presence of Sc(OTf) as a catalyst. The reactions proceeded with complete diastereoselectivity and excellent stereospecificity to provide indolines containing three contiguous stereocenters. The valuable boronic ester moiety remains in the product and allows for subsequent functionalization.
A simple, highly diastereoselective, Lewis acid catalyzed Friedel-Crafts coupling of a cyclic allylic alcohol with resorcinol derivatives has been developed. The method was applied for the enantiospecific total syntheses of structurally diverse natural products such as machaeriol-D, Δ(8)-THC, Δ(9)-THC, epi-perrottetinene and their analogues. Synthesis of both natural products and their enantiomers has been achieved with high atom economy, in a protecting group free manner and in less than 6 steps, the longest linear sequence, in a very good overall yield starting from R-(+) and S-(-)-limonene.
Sn(OTf) -catalyzed 1,3-aminobromination of donor-acceptor cyclopropanes with various sulfonyl amides or electron-poor anilines and N-bromosuccinimide is reported. These experimentally straightforward reactions occurred with complete regio- and stereospecificity (for anilines) to give γ-aminated α-brominated malonic diesters in good to excellent yields (up to 98 %). These compounds served as valuable substrates for subsequent reactions to provide substituted azetidines and γ-lactams in high yields.
AlBr-mediated multicomponent 1,3-bifunctionalization of donor-acceptor cyclopropanes using arenes and nitrosoarenes as coupling partners is presented. In the cascade, a C-C, a C-N, and a C-Br bond is formed. Reactions are easy to conduct and proceed under mild conditions. The γ,γ-disubstituted N-arylated α-amino esters obtained as products are readily further chemically modified rendering the method valuable.
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