Substitution reactions methylating agents used

Substitution Reactions. Alkylating agents containing primary alkyl or methyl groups react with (1) in synthetically useful yields (eqs 4 and 5). Reaction of (1) with 1,2-dibromoethane affords (2), while the use of metal or metalloidal halides generally results in high yields of coupling products (eqs 6-9). ... 

In an initial step the reactive formylating agent is formed from N,N-dimethylformamide (DMF) 2 and phosphorus oxychloride. Other N,N-disubstituted formamides have also found application for example A -methyl-A -phenylformamide is often used. The formylating agent is likely to be a chloromethyl iminium salt 4—also called the Vilsmeier complex (however its actual structure is not rigorously known)—that acts as the electrophile in an electrophilic substitution reaction with the aromatic substrate 1 (see also Friedel-Crafts acylation reaction) ... 

In a one-pot synthesis of thioethers, starting from potassium 0-alkyl dithiocarbonate [36], the base hydrolyses of the intermediate dialkyl ester, and subsequent nucleophilic substitution reaction by the released thiolate anion upon the unhydrolysed 0,5-dialkyl ester produces the symmetrical thioether. Yields from the O-methyl ester tend to be poor, but are improved if cyclohexane is used as the solvent in the hydrolysis step (Table 4.13). In the alternative route from the 5,5-dialkyl dithiocarbonates, hydrolysis of the ester in the presence of an alkylating agent leads to the unsymmetrical thioether [39] (Table 4.14). The slow release of the thiolate anions in both reactions makes the procedure socially more acceptable and obviates losses by oxidation. 

Many dialkyl and diaryl cadmium compounds have found use as polymerization catalysts. For example, the diethyl compound catalyzes polymerization of vinyl chloride, vinyl acetate, and methyl methacrylate (45), and when mixed with TiCl can be used to produce polyethylene and crystalline polypropylene for filaments, textiles, glues, and coatings (45). With >50% TiCl diethyl cadmium polymerizes dienes. Diethyl cadmium maybe used as an intermediate ethylating agent in the production of tetraethyllead. The diaryl compounds such as diphenylcadmium [2674-04-6]> (C H Cd, (mp 174°C) are also polymerization catalysts. These compounds are also prepared using Grignard or arylUthium reagents in tetrahydrofiiran (THF) solvent but may be prepared by direct metal substitution reactions such as ... 

Although not officially a transformation involving carboxylate, the anion formed by two electron reduction of l-methyl-4-(methoxycarbonyl)pyridinium iodide has been extensively used as an electron transfer agent in the study of aliphatic nucleophilic substitution reactions [80]. 

We interpreted the constancy of p for the reaction of substituted aromatic nucleophiles with methylating agents of varying reactivity as evidence of lack of curvature in a log k versus log K plot and hence an invariability of a (the slope of this plot) with reactivity of the methylating agent. Two entirely different factors may result in this one factor is an inherent part of the Marcus treatment, and the other is a problem of the relation between the position of the transition state along the reaction coordinate and the slope of LFERs, such as used to define the Hammett p. 

An example of electrophilic substitution has been provided, however, in the formylation of 6,6-diphenylfulvene by a Vilsmeier reaction [36], while an acetylation has been achieved in a two-phase system with a phase transfer agent, using methyl iodide, carbon monoxide, sodium hydroxide and dicobaltoctacarbonyl [241]. 

Suspension polymerization was applied to prepare polynor-bomene aosslinked beads suitable for use as supports in organic synthesis. The monomers used included norbor-nene, norbom-2-ene-5-methanol, and aosslinking agents including bis(norbom-2-ene-5-methoxy)alkanes, di(norbom-2-ene-5-methyl)ether, and l,3-di(norbom-2-ene-5-methoxy) benzene. The initial resins, which were unsaturated, were subsequently modified using hydrogenation, hydrofluorination, chlorination, or bromination to yield saturated resins with varying properties. They were reported to be superior to more traditional styrene-divinylbenzene resins due to reduced interference in electrophilic aromatic substitution reactions (e.g., Friedel-Crafts acylation and nitration). 

In contrast to the hydrolysis of prochiral esters performed in aqueous solutions, the enzymatic acylation of prochiral diols is usually carried out in an inert organic solvent such as hexane, ether, toluene, or ethyl acetate. In order to increase the reaction rate and the degree of conversion, activated esters such as vinyl carboxylates are often used as acylating agents. The vinyl alcohol formed as a result of transesterification tautomerizes to acetaldehyde, making the reaction practically irreversible. The presence of a bulky substituent in the 2-position helps the enzyme to discriminate between enantiotopic faces as a result the enzymatic acylation of prochiral 2-benzoxy-l,3-propanediol (34) proceeds with excellent selectivity (ee > 96%) (49). In the case of the 2-methyl substituted diol (33) the selectivity is only moderate (50). 

The alkyl halide must be one that reacts readily by an Sn2 mechanism. Thus, methyl and primary alkyl halides are the most effective alkylating agents. Elimination competes with substitution when secondary alkyl halides are used and is the only reaction observed with tertiary alkyl halides. 

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