Constrained Carbenes

Abstract

Carbenes traditionally have been used for cyclopropane synthesis but little else, since their reactions are difficult to control. However, the burgeoning discipline of supramolecular carbene chemistry—reactions in which highly reactive, divalent carbon intermediates are generated within the confines of host compounds—is making steady progress towards solving this problem. Various carbenes generated within cyclodextrins, hemicarcerands, and zeolites demonstrate increased selectivities and lifetimes since their usual decay pathways are blocked. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Dextran hydrogel coated surface plasmon resonance imaging (SPRi) sensor for sensitive and label-free detection of small molecule drugs

“…In this report, we applied the graft-to strategy by attaching dextran molecules to the gold substrate via a photo-cross-linking method. The photo-cross-linker we used produces a carbene group under UV irradiation, and covalently attaches the polymers via carbon insertion, addition, reaction with nucleophiles, etc [24]. A layer of carboxyl-terminated PEG-thiol was added to the gold surface as a foundation layer for the attachment of photo-cross-linking molecule.…”

Recent Advances in Chemical Biology Using Benzophenones and Diazirines as Radical Precursors

“…DAZs are used as carbene precursors that liberate molecular nitrogen and a carbene upon longwave irradiation (~360 nm). Upon irradiation, DAZs can generate a carbene by liberating nitrogen directly, or by rearrangement to yield a diazoalkane which liberates nitrogen, thereby forming a carbene indirectly [32][33][34]. When aliphatic DAZs were first discovered, their utility was limited due to their tendency to undergo 1,2-H shifts [33,34].…”

“…Upon irradiation, DAZs can generate a carbene by liberating nitrogen directly, or by rearrangement to yield a diazoalkane which liberates nitrogen, thereby forming a carbene indirectly [32][33][34]. When aliphatic DAZs were first discovered, their utility was limited due to their tendency to undergo 1,2-H shifts [33,34]. Initial efforts in the 1960s aimed at using carbene precursors such as diazoacetates for PL [35] which were later superseded by phenyldiazirines and spiro-adamantane-2,2 -diazirine, as introduced by Bayley and Knowles in 1978 [36].…”

“…Presumably, carbenes resulting from homolytic cleavage are triplet carbenes (two unpaired electrons, each occupying a different orbital), whereas a heterolytic cleavage results in a singlet carbene (two paired electrons in same orbital), even though the triplet carbene is lower in energy (Figure 4c). The carbenes generated from DAZs, like other carbenes, are usually closed-shell singlet carbenes (Figure 4a) unless a photosensitizer is used to promote intersystem crossing to the triplet state (Figure 4c) [34,38]. Carbene spin-states can be influenced by substituents and solvent effects [39].…”

Teaching old molecules new tricks: repurposing investigational drugs as chemical probes

“…203,204 Carbenes can undergo a range of reactions depending on their spin state, either singlet or triplet. 205 Crucially, singlet carbenes undergo C-H and heteroatom-H insertion to cross-link with proximal species. 206,207 Scheme 7.4.…”