Hiyama coupling reaction of fluorous alkenyl-fluorosilanes: Scope and mechanistic considerations
摘要:
Novel fluorous alkenyl-fluorosilanes (CnF2n+1CH=CHSiMe2F; n = 4, 6, 8; 5a-c) were synthetized in a three step procedure from perfluoroalkyliodides and dimethylvinylchlorosilane. They were first reacted with iodobenzene at room temperature in Hiyama coupling reaction (DMF, Pd(OAc)(2), TBAF, 72 h) to afford the appropriate omega-perfluoroalkyl-styrenes (CnF2n+1CH=CHC6H5, n = 4, 6, 8): then the reactivity of 5a with monosubstituted iodobenzenes was studied. The coupling reaction of Sa with o-substituted iodobenzenes usually failed, while that of with the m- and p-substituted ones gave fluorous styrenes [m- or p-(C4F9CH=CH)C6H4X], independently of the electronic effect of their substituent (X = Br, CF3, CH3, OCH3). These volatile products can easily be isolated by steam-distilltaion and purified further by distillation. The mechanism of the above coupling reactions was a pure Hiyama type involving fluoride-ion induced transmetallation without any Heck type contribution, since no coupling product of C6F13CH=CH2 and C6H5I was observed in blank control experiments using similar conditions (DMF, TBAF, Pd(OAc)(2), 72 h, 25 degrees C). (c) 2012 Elsevier B.V. All rights reserved.
Fluoroalkenylation of boronic acids <i>via</i> an oxidative Heck reaction
作者:Da Seul Lee、Eun Jin Cho
DOI:10.1039/c9ob00332k
日期:——
A fluoroalkenylation of boronicacids with fluoroalkyl alkenes has been developed. The Pd-catalyzed oxidative Heck coupling reaction proceeds under an oxygen atmosphere at room temperature, in the absence of a base and/or a ligand, showing excellent practicality of the process. This simple transformation is highly stereoselective to provide only E-isomers. In addition to the general approach using
Siloxane based syntheses of fluorous ethenes and their tandem Heck reactions with aryl iodides
作者:Ágnes Csapó、József Rábai
DOI:10.1016/j.jfluchem.2012.07.010
日期:2012.12
Perfluoroalkyl-ethenes (RfnCH=CH2, 6a-c; a, n = 4; b, n = 6; c, n = 8) were prepared in good isolated yields (67-89%) and high purity (GC assay > 98%) from various fluorinated organosilanes in fluoride-anion assisted protodesilylation reactions. The environmentally more benign 'KF/NEt3/H2O' reagent combination introduced here was found as an effective substitute for the commonly used tetrabutylammonium-fluoride trihydrate (TBAF center dot 3H(2)O) as a fluoride source. Fluorous styrenes ((E)-RfnCH=CH-Ar, 8) were then prepared in good isolated yields (58-93%/iodoarene) and purities (GC assay > 95%) with the Pd(0) catalyzed Heck coupling of iodoarenes (Ar-1, 7) and perfluoroalkyl-ethenes generated in situ by the fluoride assisted cleavage of (beta-perfluoroalkyl-alpha-iodo-ethyl)-siloxane ((RfnCH2CH(I)SiMe2](2)O, 3) precursors in DMF solution at elevated temperatures. They are accessible by the one-pot reaction of dimethylvinylchlorosilane (CH2=CHSiMe2Cl, 2) and perfluoroalkyl iodides (R-I, 1) as we reported earlier. Similarly, the radical chain addition of C8F17I to CH2=CHSi(OMe)(3) (9) gave (beta-perfluorooctyl-alpha-iodo-ethyl)-trimethoxysilane ([C8F17CH2CH(I)]Si(OMe)(3), 10) in good yield, which then was reacted with silica gel in dry toluene to obtain an SiO2-bonded (perfluorooctyl)ethene surrogate [silica(-O-)(3)Si-CH(I)CH2C8F17, 11]. The fluoride assisted cleavage of 11 and tandem Heck reaction with iodobenzene afforded the appropriate cross-coupled product (E)-C8F17CH=CHPh. (C) 2012 Elsevier B.V. All rights reserved.