Cobalt-Catalyzed Cross-Couplings between Alkenyl Acetates and Aryl or Alkenyl Zinc Pivalates
作者:Jie Li、Paul Knochel
DOI:10.1002/anie.201805486
日期:2018.8.27
(5 mol %) in the presence of 2,2′‐bipyridyl (5 mol %) enables electrophilic alkenylations between easily accessible alkenyl acetates or tosylates and various functionalized aryl zinc pivalates at ambient temperature. This cobalt‐catalyzed process was further applicable to alkenyl zinc pivalates to provide substituted 1,3‐dienes.
Reduction of acyl enolates of .ALPHA.-substituted .BETA.-keto esters by bakers' yeast.
作者:Hiromichi OHTA、Naoki KOBAYASHI、Takeshi SUGAI
DOI:10.1271/bbb1961.54.489
日期:——
Enol esters of 2-substituted-3-oxoalkanoates of (Z)-configuration were reduced by bakers' yeast to chiral 2-substituted-3-hydroxyalkanoates. The syn-selectivities of this reaction increased compared with those of the reduction of the corresponding racemic keto esters. The reaction may proceed via an asymmetric hydrolysis of the enol esters, followed by the reduction of the resulting carbonyl group.
Use of Cyclic β-Keto Ester Derivatives in Photoadditions. Synthesis of (±)-Norasteriscanolide
作者:Gordon L. Lange、Michael G. Organ
DOI:10.1021/jo960088s
日期:1996.1.1
The [2 + 2] photoaddition of 2-cyclopentenones with derivatives of the cyclic beta-keto ester 1 was investigated. The resultant adducts then underwent fragmentation to 5/8 fused ring systems present in terpenoid natural products such as asteriscanolide (3). For example, photoaddition of 2-cyclopentenone with the trimethylsilyl derivative 13 gave the head-to-head cis-anti-cis adduct 14. Monomethylation and borohydride reduction of the adduct yielded lactone 19. Cleavage of the silyl ether in 19 with fluoride ion followed by spontaneous fragmentation gave norasteriscanolide (20). Substrate 20, which possesses all the stereochemical features of the natural product 3 but lacks two methyl groups, was synthesized in only four steps using this methodology.
Chromium(II)-Catalyzed Diastereoselective and Chemoselective Csp<sup>2</sup>–Csp<sup>3</sup> Cross-Couplings Using Organomagnesium Reagents
A simple protocol for performing chromium-catalyzed highly diastereoselective alkylations of arylmagnesium halides with cyclohexyl iodides at ambient temperature has been developed. Furthermore, this ligand-free CrCl2 enables efficient electrophilic alkenylations of primary, secondary and tetiary alkylmagnesium halides with readily available alkenyl acetates. Moreover, this chemoselective C‒C coupling
作者:Dominik Gärtner、André Luiz Stein、Sabine Grupe、Johannes Arp、Axel Jacobi von Wangelin
DOI:10.1002/anie.201504524
日期:2015.9.1
unreactive in cross‐coupling reactions which mostly employ more electrophilic halides or activated esters (triflates, tosylates). Acetates are cheap and easily accessible electrophiles but have not been used in cross‐couplings because the strong CO bond and high propensity to engage in unwanted acetylation and deprotonation. Reported herein is a selective iron‐catalyzedcross‐coupling of diverse alkenyl