Bromine-Radical-Mediated Bromoallylation of C-C Unsaturated Bonds: A Facile Access to 1,4-, 1,5-, 1,6-, and 1,7-Dienes and Related Compounds

The radical bromoallylation of alkynes, allenes, and vinylidene cyclopropanes proceeds efficiently in the presence of a radical initiator to give 2-bromo-substituted 1,4-, 1,5-, and 1,6-diene derivatives, respectively. Three-component reactions comprised of allenes, electron-deficient alkenes, and allyl bromides give 1,7-dienes in good yields. The bromoallylation of an arylalkene can override 13-scission of the bromine radical from 13-bromoalkyl radicals to give 5-bromoalkenes, whilst the bromoallylation of vinylcyclopropanes is accompanied by 5-exo ring closure to give 1-(bromomethyl)-2-vinylcyclopentane derivatives in good yields. All of the products contain a reactive vinyl bromide moiety, which can be readily functionalized by Pd -catalyzed cross-coupling and radical cascade reactions.

Automated summary

The radical bromoallylation of alkynes, allenes, and vinylidene cyclopropanes can proceed efficiently in the presence of a radical initiator to give different diene derivatives. Three-component reactions involving allenes, electron-deficient alkenes, and allyl bromides can provide good yields of 1,7-dienes. The reaction of arylalkenes with allyl bromides can selectively produce 5-bromoalkenes, while the bromoallylation of vinylcyclopropanes results in 5-exo ring closure to yield 1-(bromomethyl)-2-vinylcyclopentane derivatives with high yields. All of the products contain a reactive vinyl bromide moiety, which can be easily functionalized through Pd-catalyzed cross-coupling and radical cascade reactions.