Pyridine-Catalyzed Radical Borylation of Aryl Halides
作者:Li Zhang、Lei Jiao
DOI:10.1021/jacs.6b11813
日期:2017.1.18
A pyridine-catalyzed transition-metal-free borylation reaction of haloarenes has been developed based on the selective cross-coupling of an aryl radical and a pyridine-stabilized boryl radical. Arylboronates were produced from haloarenes under mild conditions. This borylation reaction features a broad substrate scope, operational simplicity, and gram-scale synthetic ability.
The reduction of alkenyl halides with tributyltinhydride in the presence of a catalytic amount of tetrakis(triphenylphosphine)palladium has been studied. Alkenyl iodides reacted easily with tributyltinhydride at 25°C to give the corresponding hydrocarbons stereoselectively. However, the reaction of alkenyl bromides were sluggish at 25°C and needed heating at 75°C to complete.
Halogen-magnesium exchange of various aryl halides is achieved with a magnesium ate complex at low temperatures; Tributylmagnesate ((Bu3MgLi)-Bu-n) induces facile iodine-magnesium exchange at -78 degreesC. Dibutylisopropylmagnesate ((PrBu2MgLi)-Pr-i-Bu-n) is more reactive than (Bu3MgLi)-Bu-n, and this reagent accomplishes selective bromine-magnesium exchange at -78 degreesC. This procedure is utilized for the preparation of various polyfunctionalized arylmagnesium species. The exchange of alkenyl halides using this method proceeds with retention of configuration of the double bond.