Formation of Chiral Allylic Ethers via an Enantioselective Palladium-Catalyzed Alkenylation of Acyclic Enol Ethers
作者:Harshkumar H. Patel、Matthew B. Prater、Scott O. Squire、Matthew S. Sigman
DOI:10.1021/jacs.8b02751
日期:2018.5.9
palladium-catalyzed process to access highly functionalized, optically active allylic aryl ethers. A number of electron-deficient alkenyl triflates underwent enantioselective and site-selective coupling with acyclic aryl enol ethers in the presence of a chiral palladium catalyst. This transform provides chiral allylicether products in high yields and excellent enantiomeric ratios, furnishing a unique
and useful synthons for the synthesis of Famvir®, an antiviral drug. Simple methods for the preparation of 2-haloalkylidenemalonates are not available. We have developed a novel and non-cumbersome methodology for the synthesis of dialkyl 2-(2-haloethylidene)malonates, cyanoacetates and halocrotonates by one carbon extension of dialkyl (2-alkoxymethylene)malonates, cyanoacetates and 3-alkoxyacrylates with
Pd(CO)(PPh3)3, Pd3(CO)3(PPh3)4, Pd3(CO)3(PPh3)3, and PdCl2(PPh3)2 were found to be excellent catalysts for the carboxymethylation of various organic halidesunderverymildconditions. The carboxymethylation reaction is considered to proceed via acyl complexes as the intermediates.
The reaction of benzimidazolium salt (3) and polarized olefins (1a,b,d and 2c) with K2CO3 in CHCl3 gave the corresponding benzimidazolium N-allylides (4a-d). Thermolyses of N-allylides (4a,b) in refluxing xylene afforded the 1,5-dipolar cyclization product, benzopyrroloimidazole (5a), whereas heating of N-allylides (4c,d) resulted in back-donated 1,6-cyclization to give the mesomeric betaines, benzimidazopyridiniumides (7a,b). Treatment of 3 and 2a with K2CO3 in CHCl3 yield directly benzopyrroloimidazole (5b), while similar treatment of 3 with 1c or 2b gave benzopyrrolopyrazines (6a,b).