Remote 1,4-Carbon-to-Carbon Boryl Migration: From a Mechanistic Challenge to a Valuable Synthetic Application of Bicycles

The present paper reports a remote carbon-to-carbon boryl migration via an intramolecular 1,4-B/Cu shift, which establishes an in situ stereospecific electrophilic trap on the alkene moiety. The synthetic application is developed to prepare functionalized cyclopentenes by means of a palladium-catalyzed regioselective intramolecular coupling that completes a strategic cyclopropanation and generates valuable structural bicyclic systems. The mechanism is characterized by DFT (density functional theory) calculations which showed that the 1,4-migration proceeds through an intramolecular, nucleophilic attack of the copper-alkyl moiety on the boron atom bonded to the C(sp2), leading to a 5-membered boracycle structure. The computation of the 1,3- and 1,4-B/Cu shifts is also compared as is the impact of the endo- or exocyclic alkene on the reaction kinetics. The intramolecular 1,4-B/Cu shift justifies the observed remote carbon-to-carbon boryl migration, which makes stereoselective electrophilic trapping on the alkene moiety possible. Subsequent palladium-catalyzed regioselective intramolecular coupling enables functionalized cyclopentenes to be prepared that complete strategic cyclopropanation and deliver structurally valuable bicyclic systems. DFT mechanistic studies show that remote boryl migration occurs efficiently through 5-membered boracycle intermediates. image