Vinyl radicals, generated from the reaction of vinyl iodides with tributylstannyl radical, react with electron-deficient alkenes to give di- or trisubstitutedalkenes in moderate to good yields. The stereoselectivity is largely dependent on the substituent at 1- and 2-position of vinyl iodides.
Palladium-Catalyzed Regioselective C–H Iodination of Unactivated Alkenes
作者:Benedikt S. Schreib、Erick M. Carreira
DOI:10.1021/jacs.9b03998
日期:2019.6.5
A palladium-catalyzedC-H iodination of unactivated alkenes is reported. A picolinamide directing group enables the regioselective functionalization of a wide array of olefins to furnish iodination products as single stereoisomers. Mechanistic investigations suggest the reversible formation of a six-membered alkenyl palladacycle intermediate through a turnover-limiting C-H activation.
The nickel-catalyzed electroreductive conjugate addition of (Z)- or (E)-alkenyl halides to electron-deficient olefins in the presence of a sacrificial iron rod as the anode proceeds with complete retention of the stereochemistry of the alkenyl part and affords functionalized isomerically pure (Z)- or (E)-olefins in high yield.
Homo- and cross-coupling involving alkenyl halides have been performed efficiently using an electroassisted nickel-complex catalysis. Valuable product such as conjugated dienes, beta,gamma- or gamma,delta-unsaturated esters, ketones, or nitriles, as well as alkenylated aryl compounds are thus prepared with high yields and high stereoselectivity. Partial isomerization is only observed in a few cases, when the alkenyl halide is involved in a late step of the catalytic cycle. This is the case in the preparation of (Z,Z)-1,3-diene.