Methyl cations reactions, with

The silyl triflate 8 (Scheme 3) shows an ambireactive behavior of the cation. Reaction with a methylmagnesium chloride or water leads to the methyl-substituted product and to the siloxane, respectively, as expected for an electrophilic silicon center. An oxonium ion reactivity is observed in the reaction with neutral Lewis bases such as triethylamine and trimethylphosphine. 

Quaternary ammonium alkyl ethers are prepared similarly an alkaline starch is reacted with a quaternary ammonium salt containing a 3-chloto-2-hydtoxyptopyl or 2,3-epoxyptopyl radical. Alternatively, such derivatives can be prepared by simple quaternization of tertiary aminoalkyl ethers by reaction with methyl iodide. Sulfonium (107) and phosphonium (108) starch salts have also been prepared and investigated. Further work has explained the synthesis of diethyl aminoethyl starch (109) as well as the production of cationic starches from the reaction of alkaline starch with... 

The second group of reactions is called vicinal difunctionalization. They embrace the C2 and C3 positions of the furan ring simultaneously. Thus, complex 3 (X = O, R = R = R = H) reacts with benzaldehyde dimethyl acetal to give 4H-furanium cation (the product of electrophile addition at C4), which experiences further attack by the methoxide group with formation of the acetal 8 (950M2861). This reaction is possible in the presence of the Lewis acid (BF3—OEt2). Reaction with methyl vinyl ketone in methanol, when run in identical conditions. 

In Eq. (3), the unstable methyl diazonium ion decomposes by S l reaction into nitrogen and a methyl cation w hich combines with the anion Z to give CH3—Z. In Eq. (4) an Sk2 reaction occurs. The loss of the nitrogen from CH3—here takes place only wdth the participation of the anion as nucleophile. 

In Ref.125) the calculation of an activation barrier for reaction (21) in the gas phase is considered to be an error of the MINDO/3 method and the process is assumed to be activationless. But in respect to the medium effect a barrier of 54 k J mol-1 is obtain-ed which agrees again with the results from Huron-Claverie calculations. Bertran et al. calculated the influence of the solvation on the electrophilic attack of a proton 133) or a methyl cation 134,135) on ethene using a MINDO/3 supermolecule model. Smaller reaction enthalpies also result in solution than in the gas phase in addition to the appearance (H+ + ethene) or the increase (CH 4 + ethene) of an activation barrier1361. 

Products 19 and 20 result from the collapse of vinyl cation 23 with Cl to give 19, and the subsequent reaction of this product with HCl gives 20. Compounds 21 and 22 could arise from either a 1,2-methyl shift to vinyl cation 23 or... 

Deoxy-6-fluoro-L-ascorbic acid ° (314) was prepared from methyl 2,3-<9-isopropylidene-6-0-tosyl-a-L-gulosonate (313) by reaction with KP followed by isomerization of the product (with H" " cation-exchange resin). 

By utilizing a combination of RAFT and cationic ROP, the synthesis of [poly(methyl methacrylate)][poly(l,3-dioxepane)][polystyrene] miktoarm star terpolymers was achieved [182], The approach involved the synthesis of PS functionalized with a dithiobenzoate group by RAFT polymerization and subsequent reaction with hydroxyethylene cinnamate (Scheme 98). The newly created hydroxyl group was then used for the cationic ring opening polymerization of 1,3-dioxepane (DOP). The remaining dithiobenzoate group was used for the RAFT polymerization of methyl methacrylate. 

Methylation of the dihaptothioacyl complex 22 affords compound 23 containing a bidentate carbene ligand, which on reaction with chloride ion leads to the neutral monodentate carbene complex 24 (50,51). The chelate carbene complex 26 is generated in a novel interligand reaction from the thiocarboxamidothiocarbonyl cation 25. The thiocarbonyl carbon acts as the electrophilic component in this reaction, and 26 is further alkylated to a bidentate dicarbene species (52). 

---