A copper-catalyzedC(sp3)-Si cross-coupling of aliphatic C(sp3)-I electrophiles using a Si-B reagent as the silicon pronucleophile is reported. The reaction involves an alkyl radical intermediate that also engages in 5-exo-trig ring closures onto pendant alkenes prior to the terminating C(sp3)-Si bond formation. Several Ueno-Stork-type precursors cyclized with excellent diastereocontrol in good yields
Iron-Catalyzed Tandem Cyclization and Cross-Coupling Reactions of Iodoalkanes and Aryl Grignard Reagents
作者:Jae Gon Kim、Young Hoon Son、Jin Won Seo、Eun Joo Kang
DOI:10.1002/ejoc.201403511
日期:2015.3
Several experimental results, such as cyclopropyl ring opening, the stereochemical outcome of the reaction with a secondary iodide substrate, and intermediate identification with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), support the conclusion that a radical process is involved in this catalytic system. Moreover, deuterium labeling experiments indicated that radical disproportionation could occur in
Stereoselective Synthesis of Heterocyclic Zinc Reagents via a Nickel-Catalyzed Radical Cyclization
作者:Andrea Vaupel、Paul Knochel
DOI:10.1021/jo960617s
日期:1996.1.1
Unsaturated iodo or bromo acetals of type 2 undergo a smooth cyclization mediated by diethylzinc (2 equiv) and Ni(acac)(2) as catalyst (2-5 mol %). These cyclizations proceed via a radical mechanism affording a (tetrahydrofuranylmethyl)zinc halide of type 1, which can be reacted with various electrophiles after a transmetalation with CuCN . 2LiCl. High stereoselectivities are usually observed in the ring closures, especially if monocyclic cyclization precursors are used. In these cases, bicyclic products of the endo-configuration are obtained with over 94% diastereoselectivity. The synthetic method has been extended to the preparation of a nitrogen heterocycle and over 98% pure trans-4,5-disubstituted gamma-butyrolactones. A short enantioselective synthesis of (-)-methylenolactocine (3) using the radical cyclization and a novel oxidation of alpha-silyl zinc peroxide as a key step is also described.