Small rings in the bigger picture: ring expansion of three- and four-membered rings to access larger all-carbon cyclic systems

Abstract

Ring-expansion of strained small-size rings to forge larger all-carbon ones, allows a rapid build-up of molecular complexity.

Asymmetric β-arylation of cyclopropanols enabled by photoredox and nickel dual catalysis

“…Cyclopropanes are versatile building blocks and participate in a diverse range of fundamental transformations in organic synthesis by taking advantage of their intrinsic high ring strain. 1 Among these cyclopropane derivatives, cyclopropanols, which are usually considered as precursors of ketone homoenolates, have gained emerging interest as three-carbon synthons for new bond formation and natural product synthesis in recent years. 2 In the presence of transition metal (TM) catalysis or single electron transfer (SET) catalysis, they have been widely applied in the synthesis of β-functionalized ketones by involving intermediates of homoenolates or β-keto radicals generated via ring-opening pathways, albeit mostly in racemic forms ( Scheme 1A ).…”

Kinetic stabilization allows structural analysis of a benzoborirene

“…1–3 Deviations from ideal bonding arrangements result in an increased energy content compared to a hypothetical unstrained reference. The high energy content not only makes strained compounds highly reactive and thus valuable for chemical transformations, 4–11 but strain can also result in unusual structures that allow testing the limits of the theory of chemical bonding. Outstanding examples are the platonic hydrocarbons tetrahedrane and cubane that feature strongly distorted tetracoordinate carbon atoms.…”

Palladium-Catalyzed Access to Benzocyclobutenone-Derived Ketonitrones via C(sp2)–H Functionalization

“…The strain inherent in four-membered rings renders them versatile building blocks in organic synthesis. 1 In particular, benzocyclobutenes (BCBs) have been recognized as valuable synthons with numerous synthetic applications disclosed in recent decades, 2 often relying upon the four-membered ring opening to o -quinodimethane derivatives, followed by cycloaddition restoring the aromaticity of the benzene ring. 3 In the past few years, new modes of BCBs transformations were actively developed, initiated by cleavage of the proximal 4 or distal 5 C–C bond or involving C–H functionalization 6 or ring expansion upon addition of nucleophiles.…”