Alkylating reagents dialkyl acetals

Derivatization (GC) 848 alkylating reagents 861 alkyl halide/catalyst 861 dialkyl acetals 863 diazoalkanes 862 extractive alkylation 863 pyrolytic alkylation 865 al) ldimethylsilyl reagents 855... 

Several further publications report on the (—)-sparteine-mediated addition of alkyl-or aryllithium onto imines or the C=N bond of isoquinolines . Usually, the achieved enantiomeric excesses are low and, sometimes, other chiral ligands serve better. As reported by Muller and coworkers, the nucleophilic substitution of arenecarbaldehyde dialkyl acetals by o-substituted aryllithium reagents is an alternative . 

When a-keto acetic acid is treated with one mole of a base, the methylene group which is more acidic reacts with the base. And the reaction with an alkylation reagent gives alkyl products attached to methylene. When this reaction is repeated in the next step, the other hydrogen can also react to a dialkyl product. The two alkylation agents may be the same or different (R, R"). 

Reaction with RCHO and acetals.1 In the presence of dibutyltin bis(tri-fiuoromethanesulfonate), 2,3 this reagent converts aldehydes or their dialkyl acetals or ethylene acetals into 2-alkyl-1,3-dithianes (70-85% yield). However, the reagent differentiates between aldehydes and acetals as shown in the examples. An aliphatic... 

Both acidic H atoms of a malonic ester can be replaced by alkyl groups. These dialky-lated malonic esters are formed by successively removing the acidic protons with sodium alkoxide and treatment of the enolates with an alkylating reagent. The subsequent hydrolysis and decarboxylation of these dialkylated malonic esters affords a,a-dialkylated acetic acids as another class of products accessible via the malonic ester synthesis. 

Other alkylating agents which have been used include diazomethane [2], trialkyl phosphates [11], alkoxypho.sphonium salts [12], dimethylformamide dialkyl acetals [13], trialkyl orthoformates [14], alkyl cyanoformates [15], dialkyl carbonates (less toxic) [16] and, where more powerful reagents arc needed, alkyl fluorosulfonates, trialkyloxonium tetrafluoroborates [17], alky] triflates and mesylates [18, 19]. 

Alkylation describes the reaction where an active hydrogen is replaced with an alkyl group, for example, a methyl group. Most polar groups can be alkylated, and many reagents can be used, for example, alkyl halogenides, diazo alkanes, and N,N -dimethylformamide dialkyl acetal. An example of an alkylation is the formation of methyl esters of fatty acids by using methanolic BF3, where boron trifluoride (BF3) acts as a catalyst. 

It seems likely that dichloromethane could be used in this procedure instead of dibromomethane because after the first chlorine has been substituted, the second substitution should be extremely fast. Cyclization to form a five-membered ring is a favorable process and the alkylating reagent at this stage will be an alkoxymethyl halide. Substitution of the first chlorine in dichloromethane is not improbable, especially in light of the known reaction of both alkoxide and phenoxide anions with it under phase transfer conditions to yield symmetrical dialkyl or diaryl acetals of form-... 

Silyi enol ethers can be dimerized to symmetrical 1,4-diketones by treatment with Ag20 in DMSO or certain other polar aprotic solvents." The reaction has been performed with R , R = hydrogen or alkyl, though best yields are obtained when r = r = H. In certain cases, unsymmetrical 1,4-diketones have been prepared by using a mixture of two silyi enol ethers. Other reagents that have been used to achieve either symmetrical or cross-coupled products are iodosobenzene-Bp3-Et20," ceric ammonium nitrate," and lead tetraacetate." If R =0R (in which case the substrate is a ketene silyi acetal), dimerization with TiCU leads to a dialkyl succinate (34, r =0R)." ... 

Selective activation of hydroxyl groups by the stannylation procedure is an established practice to efficiently manipulate diols and polyols [53, 54]. Among the various reagents and methods, activation through dialkylstannylene acetals is noteworthy. This two-step protection method involves the conversion of dihydroxy substrates into cyclic dialkyl dioxastan-nanes which, in turn, are treated with suitable nucleophiles, to regioselectively afford the corresponding mono alkyl, silyl or acyl derivatives under neutral conditions. 

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