RESUMO
A novel visible-light-induced radical cascade bromocyclization of N-arylacrylamides has been accomplished. This reaction overcomes the overbromination at the benzene rings suffered in traditional electrophilic reactions, thus enabling the first highly chemoselective synthesis of valuable 3-bromomethyloxindoles. The combination of pyridine and anhydrous medium is identified as the key factor for the high chemoselectivity in the current photoreaction system, which might work by suppressing the in situ generation of low-concentration Br2 from N-bromosuccinimide. Moreover, the mild reaction conditions ensure the generation of a wide range of the new desired products with excellent functional group tolerance.
RESUMO
In organic synthesis, incorporating two functional groups into the carbon-carbon double bond of α,ß-unsaturated amides is challenging due to the electron-deficient nature of the olefin moiety. Although a few examples of dihydroxylation of α,ß-unsaturated amides have been demonstrated, producing cis-1,2-diols using either highly toxic OsO4 or other specialized metal reagents in organic solvents, they are limited to several specific amides. We describe herein a general and one-pot direct synthesis of trans-1,2-diols from electron-deficient α,ß-unsaturated amides through dihydroxylation using oxone as a dual-role reagent in water. This reaction does not require any metal catalyst and produces non-hazardous and nontoxic K2 SO4 as the sole byproduct. Moreover, epoxidation products could also be selectively formed by adjusting the reaction conditions. By the strategy, the intermediates of Mcl-1 inhibitor and antiallergic bioactive molecule can be synthesized in one pot. The gram-scale synthesis of trans-1,2-diol which is isolated and purified by recrystallization further shows the potential applications of this new reaction in organic synthesis.
