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(sp), leading to a 5-membered boracycle structure.

Boron-Copper 1,3-Rearrangement: the New Concept Behind the Boryl Migration from C(sp ) in Alkenyl Boranes to C(sp ).

Regioselective borylcupration of borylated skipped (Z)-dienes generates diborylated alkylcopper species that are involved in an intramolecular stereospecific B/Cu 1,3-rearrangement by migration of Bpin moiety from C(sp ) to C(sp ). DFT mechanistic studies showed that boryl migration occurs through the formation of 4-membered boracycle intermediate with a moderate free-energy barrier. Moreover, the use of KOMe forms stable Lewis base adducts with Bpin moieties that blocks the reaction.

Stereoselective Cyclopropanation of 1,1-Diborylalkenes via Palladium-Catalyzed (Trimethylsilyl)diazomethane Insertion.

Palladium catalyzes the cyclopropanation of 2-substituted 1,1-diborylalkenes with (trimethylsilyl)diazomethane. The relative stereoselectivity is controlled via a carbene insertion sequence generating an exclusive conformation between the R and SiMe substituents. Mixed 1,1-diborylalkenes also contributed to the formation of stereoselective B, B, Si-cyclopropanes.