Mono-alkyl compound

Methyl, propyl, butyl, etc., malonic esters are also obtained in a similar manner. It is to be observed that aryl halides do not undergo this reaction. The di-alkyl esters are obtained from the mono-alkyl esters in the same way as the latter are obtained from malonic ester. But although di-alkyl compounds are not formed directly in any quantity, yet it frequently happens that a little is obtained in the preparation of the mono-alkyl compound from 1 mol. of sodium ethoxide and 1 mol. of alkyl halide, owing to the mono-derivative reacting with more sodium and alkyl halide. This may be prevented when necessary by using only half the calculated quantity of sodium and alkyl halide. By this means the yield of benzoyl malonic ester for example is raised from 55% to 85% in its preparation from sodium, benzoyl chloride and malonic ester. (B., 44, 1507.)... 

Control of the degree of alkylation of an amino acid is difficult. Alkylation can lead to /V-mono- and di-alkyl derivatives, or betaines RIN+—(CR R2—) C( >2, when an alkyl halide is used. Many practical devices can be employed to get the mono-alkylated compound. Schiff-base formation with an aldehyde, followed by reduction, is a standard route. 

Difficulties associated with the mono-alkylation of divinyl ketone have been neatly overcome by the use of -chloroethylvinyl ketone, making possible the construction of the tricyclic system (455) in 52% overall yield by reaction of mono-alkylated compound (453) with t-butyl aceto-acetate. The formation of (455) must proceed by multiple intramolecular aldol condensation of the intermediate 2,6,10-triketone (454). 

The ratio ARH/ARj (monoalkylation/dialkylation) should depend principally on the electrophilic capability of RX. Thus it has been shown that in the case of t-butyl halides (due to the chemical and electrochemical stability of t-butyl free radical) the yield of mono alkylation is often good. Naturally, aryl sulphones may also be employed in the role of RX-type compounds. Indeed, the t-butylation of pyrene can be performed when reduced cathodically in the presence of CgHjSOjBu-t. Other alkylation reactions are also possible with sulphones possessing an ArS02 moiety bound to a tertiary carbon. In contrast, coupling reactions via redox catalysis do not occur in a good yield with primary and secondary sulphones. This is probably due to the disappearance of the mediator anion radical due to proton transfer from the acidic sulphone. 

The synthesis of oc/S-unsaturated sulphoxides from the anion (122) has been described.113 The reaction is non-stereospecific, but good yields are obtained from cyclopentanones and acetophenones. Good yields of mono-alkylated products are obtained from the reaction of carbanions of diethyl 2-oxophosphonates (123) and reactive halides 114 alkylation of the compounds (124) has also been achieved.115 The... 

Phosphonates and related compounds, which can subsequently be used in the Wittig-Homer reaction (see Section 6.5), are readily alkylated in good yield (Table 6.8) [67-71], Mono-alkylation is observed with mildly basic conditions at 45°C [67] and dialkylation under stronger basic conditions at 60°C [70], Reaction of a,to-dihaloalkanes with phosphonocarboxylates leads to cycloalkylphosphonates [72], The methylenebisphosphonate reacts in a similar manner. 

In the preparation of some of the higher mono-alkyl acetoacetic esters the yield is sensibly lowered, owing to the formation of di-alkyl compounds due to secondary reactions of the same type as those described on p. 137. This in like manner can be remedied by using only half the calculated quantity of sodium and alkyl halide. The unattacked acetoacetic ester is recovered by distillation. 

Catalyst screening experiments resulted in the discovery that copper(salen) complex 33 was a highly effective catalyst for the conversion of alanine derivative 16b into (f )-a-methyl phenylalanine 17 under the conditions shown in Scheme 8.16. The presence of just 1 mol% of catalyst 33 was sufficient to induce the formation of compound 17 with up to 92% ee and in >70% yield [33]. Allyl bromide, 1-chloromethylnaphthalene and ethyl iodide also reacted with substrate 16b to give the corresponding (H)-a-methyl a-amino acids in the presence of 2 mol % of complex 33 [34], Complex 33 also catalyzed the asymmetric mono-alkylation of glycine-derived substrate 34 by benzylic or allylic halides, to give (H)-a-amino acid derivatives 35 with 77-81% ee. and in greater than 90% yield, as shown in Scheme 8.17. 

From acetyl-acetone a series of (3- or 1 3-diketones can be obtained by treating the mono-sodium compound with alkyl iodides ... 

Re has recently come to the forefront in liquid phase oxidation catalysis, mainly as a result of the discovery of the catalytic properties of the alkyl compound CH3Re03 [methyltrioxorhenium (MTO)]. MTO forms mono-and diperoxo adducts with H2O2 these species are capable of transferring an oxygen atom to almost any nucleophile, including olefins, allylic alcohols, sulfur compounds, amides, and halide ions (9). Moreover, MTO catalysis can be accelerated by coordination of N ligands such as pyridine (379-381). An additional effect of such bases is that they buffer the strong Lewis acidity of MTO in aqueous solutions and therefore protect epoxides, for example. 

Little is known about structural aspects of mono-alkyl and arylantimony(V) chlorides58"60, because of their unstable nature. For example, phenylantimony(V) chloride is an unstable compound, which tends to disproportionate as shown below on standing58 ... 

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