63009-74-5Relevant articles and documents
General Cyclopropane Assembly by Enantioselective Transfer of a Redox-Active Carbene to Aliphatic Olefins
Montesinos-Magraner, Marc,Costantini, Matteo,Ramírez-Contreras, Rodrigo,Muratore, Michael E.,Johansson, Magnus J.,Mendoza, Abraham
, p. 5930 - 5935 (2019/02/24)
Asymmetric cyclopropane synthesis currently requires bespoke strategies, methods, substrates, and reagents, even when targeting similar compounds. This approach slows down discovery and limits available chemical space. Introduced herein is a practical and versatile diazocompound and its performance in the first unified asymmetric synthesis of functionalized cyclopropanes. The redox-active leaving group in this reagent enhances the reactivity and selectivity of geminal carbene transfer. This effect allowed the asymmetric cyclopropanation of various olefins, including unfunctionalized aliphatic alkenes, that enables the three-step total synthesis of (?)-dictyopterene A. This unified synthetic approach delivers high enantioselectivities that are independent of the stereoelectronic properties of the functional groups transferred. Our results demonstrate that orthogonally differentiated diazocompounds are viable and advantageous equivalents of single-carbon chirons.
An exploratory study of ring closures of aryl radicals onto cyclopropyl- and oxiranyl-isocyanate acceptors
Minin, Patricia L.,Walton, John C.
, p. 2471 - 2475 (2007/10/03)
The idea that ring closures of C-centred radicals onto isocyanates could be made permanent by designing the cyclised radical to undergo a rapid onward β-scission, was investigated for the 2-(2-isocyanato)cyclopropylphenyl and 2-(2-isocyanato)oxiranylphenyl radicals. The radical precursors, trans- and cis-l-bromo-(2-isocyanatocyclopropyl)benzene and (2-bromophenyl)-3- isocyanatooxirane, were prepared from the corresponding bromophenylcyclopropane and bromophenyloxirane carboxylic acids via Curtius rearrangements of the derived azides. The structure of the trans-2-(2-isocyanato)cyclopropylphenyl radical prevents cyclization, however, it was shown that isomerisation to the analogous cis-radical occurred, probably by scission of the disubstituted cyclopropane bond followed by internal rotation of the resulting resonance stabilised diradical. It was found, however, that the main product from homolytic reactions of both trans- and cis-isocyanatocyclopropyl compounds, with tributyltin hydride and tris(trimethylsilyl)silane, was the direct reduction product, trans-(2-isocyanatocyclopropyl)benzene. Only traces of cyclised products, that were probably 4,5-dihydrobenzo[c]azepin-1-one from the cyclopropane precursor and 5H-6-oxa-8-azabenzocyclohepten-9-one from the oxirane precursor, were detected. We conclude, therefore, that the rate of cyclization onto isocyanate acceptor groups must be slower in these systems than hex-5-enyl cyclization or that the reverse ring-opening process must be faster than for analogous radicals.
