A new approach to cyclohexenes and related structures

International audienceIntermolecular radical addition of a xanthyl phosphonoacetate to a ?,d-enone gives rise to an adduct suitable for a base induced Horner-Emmons ring closure to a cyclohexene derivative, optionally after the reductive removal of the xanthate group

Vinylogous dithiocompounds for RAFT polymerization

International audienceThe present communication focuses on a novel range of dithioester agents for reversible addition fragmentation transfer polymerization (RAFT), comprising one given (ethoxycarbonyl)ethyl leaving group and an unsaturated, potentially substituted Z group. RAFT polymerization of styrene and ethyl acrylate was efficiently conducted using four original vinylogous dithio compounds. Controlled Mn with low Mw/Mn were obtained for most of the reported experiments. The peculiar addition-fragmentation mechanism of this class of RAFT agents caused a severe retardation during polymerization

Vinylogous Thionothio Compounds for RAFT Polymerization.

International audienceThe polymerization of reversible addition-fragmentation chain transfer (RAFT) using the thioether- thione B9 as a RAFT agent, was illustrated. Dithioesters A1-4 were synthesized and evaluated in RAFT polymerization of ethyl acrylate (EA) and styrene (St). The conversions were less than 10% under classical conditions for acrylate polymerizations where oligomers capped by thiocarbonylthio group of A were formulated. The results show that the creation of stabilized intermediated radical slows down the subsequent fragmentation step and therefore significantly reduces the overall rate of polymerization

Xanthates as chain-transfer agents in controlled radical polymerization (MADIX): Structural effect of the O-alkyl group

The capability of three chain-transfer agents, O-alkyl-S-(1-ethoxycarbonyl)ethyl xanthates (CH3-CHCO2C2H5)S(C=S)OZ', to control the free-radical polymerization of styrene and ethyl acrylate by the MADIX process was examined. The reactivity of the xanthates varied according to the following trend: Z' = CH2CH3 < CH2CF3 < CH[P(O)(OEt)2]CF3. This change in reactivity allowed a lowering of the polydispersity index from 2.0 for Z' = CH2CH3 to 1.15 for Z' = CH[P(O)(OEt)2]CF3 in the case of the polymerization of styrene