211861-12-0Relevant articles and documents
Catalytic, enantioselective, intramolecular carbosulfenylation of olefins. preparative and stereochemical aspects
Denmark, Scott E.,Jaunet, Alex
supporting information, p. 140 - 171 (2014/01/17)
The first catalytic, enantioselective, intramolecular carbosulfenylation of isolated alkenes with aromatic nucleophiles is described. The combination of N-phenylsulfenylphthalimide, a chiral selenophosphoramide derived from BINAM, and ethanesulfonic acid as a cocatalytic Bronsted acid induced an efficient and selective cyclofunctionalization of various alkenes (aliphatic and aromatic) tethered to a 3,4-methylenedioxyphenyl ring. Under these conditions, 6-phenylthio-5,6,7,8-tetrahydronaphthalenes are formed diastereospecifically in good yields (50-92%) and high enantioselectivities (71:29-97:3 er). E-Alkenes reacted much more rapidly and with much higher selectivity than Z-alkenes, whereas electron-rich alkenes reacted more rapidly but with comparable selectivity to electron-neutral alkenes and electron-deficient alkenes. The Bronsted acid played a critical role in effecting reproducible enantioselectivity. A model for the origin of enantioselectivity and the dependence of rate and selectivity on alkene structure is proposed along with a rationale for the site selectivity in reactions with monoactivated arene nucleophiles.
Integration of electrooxidative cyclization and chemical oxidation via alkoxysulfonium ions. Synthesis of exocyclic ketones from alkenes with cyclization
Ashikari, Yosuke,Nokami, Toshiki,Yoshida, Jun-Ichi
supporting information, p. 3322 - 3331 (2013/06/05)
An integration of electrooxidative cyclization and chemical oxidation was achieved. Electrochemical oxidation of alkenes having a nucleophilic moiety in the presence of DMSO gave cyclized alkoxysulfonium ions, which were converted to the corresponding ket
Structural effects in radical clocks and mechanisms of grignard reagent formation: Special effect of a phenyl substituent in a radical clock when the crossroads of selectivity is at a metal/solution interface
Hazimeh, Hassan,Mattalia, Jean-Marc,Marchi-Delapierre, Caroline,Kanoufi, Frederic,Combellas, Catherine,Chanon, Michel
experimental part, p. 2775 - 2787 (2009/08/16)
A large class of radical clocks is based on the intramolecular trapping of a reactive radical by a suitably located, unsaturated system. Depending on the substituents present on this unsaturated system, the rate of cyclisation may vary drastically. This property has been repeatedly used, to diagnose the participation of very short-lived radicals in the mechanisms of a wide variety of reactions. For reactions occurring in homogeneous solution, a phenyl substituent capable of stabilizing the radical formed during the act of trapping has been one of the most widely used tools of this type. During study of the mechanisms of formation of Grignard reagents - reactions that occur at the interface of the metal and the solution - the phenyl substituent displayed a specific new behaviour pattern. Besides its stabilizing role, it was also able to play the role of mediator in redox catalysis of electron transfer. In this case, the first events on the pathway to the Grignard reagents involve a cascade of three (one intermolecular followed by two intramolecular) electron transfers. Introduction of a p-methoxy substituent on the phenyl ring, making the phenyl group a poorer electron acceptor, suppresses this specific second role. Applied to the mechanism of Grignard reagent formation, this p-methoxy effect is consistent with a triggering mechanistic act of electron transfer from the metal to the aryl halide rather than with a concerted oxidative addition. A similar change in selectivity is observed, when a p-methoxy group is introduced onto a phenyl group that also bears a halogen, but its origin is different: this effect is associated with the shortening of the lifetime of the radical anion formed by the triggering electron transfer. These observations reemphasise our earlier proposals to use concepts originating from, electrochemical kinetics to explain, the selectivities of reactions occurring at metal/solution interfaces. This conjecture could possibly hold for any interface where the diffusion of reactive species plays a role in the settling of selectivity. These concepts emphasise the necessity to consider, for each reactive species, their average distance of diffusion away from the metal/solution interface. Wiley-VCH Verlag GmbH & Co. KGaA.
