Borylcyclopropanes: Synthetic Strategies and Applications.

The carbon-boron bond is among the most versatile functional groups in organic synthesis, and its installation within the strained cyclopropane framework generates borylcyclopropanes with a rich reactivity profile. The presence of a boron moiety on the cyclopropane ring unlocks a broad spectrum of transformations inaccessible to unfunctionalized cyclopropanes, including Suzuki-Miyaura cross-coupling, oxidation, amination, Matteson homologation, and stereospecific ring-opening via 1,2-metalate rearrangement to enantioenriched acyclic organoboron arrays. Meanwhile, the distinctive reactivity of boron-stabilized intermediates such as α-boryl radicals, α-boryl carbanions, and α-boryl cations enables cyclopropanation strategies with no classical counterpart. This review provides an exhaustive survey of borylcyclopropane chemistry, organized by mechanistic class: metal-carbene cyclopropanations under palladium, copper, rhodium, and enzyme catalysis; non-diazo carbene and carbenoid approaches; transition-metal-catalyzed and metal-free intramolecular nucleophilic cyclizations; photocatalytic radical pathways; iridium- and palladium-catalyzed C─H borylation; hydroboration of cyclopropenes and alkylidenecyclopropanes; and miscellaneous strategies including bicyclo[1.1.0]butane (BCB) ring-opening and 1,2-metalate rearrangements. Applications in medicinal chemistry, natural product synthesis, and the preparation of stereodefined acyclic building blocks are also discussed.