Alkylation substrate

Table 5.13. Rate Constants for Nuclei hilic Substitution in Primary Alkyl Substrates ...

In contrast, Cozzi and Umani-Ronchi found the (salen)Cr-Cl complex 2 to be very effective for the desymmetrization of meso-slilbene oxide with use of substituted indoles as nucleophiles (Scheme 7.25) [49]. The reaction is high-yielding, highly enantioselective, and takes place exclusively at sp2-hybridized C3, independently of the indole substitution pattern at positions 1 and 2. The successful use of N-alkyl substrates (Scheme 7.25, entries 2 and 4) suggests that nucleophile activation does not occur in this reaction, in stark contrast with the highly enantioselective cooperative bimetallic mechanism of the (salen)Cr-Cl-catalyzed asymmetric azidolysis reaction (Scheme 7.5). However, no kinetic studies on this reaction were reported. 

TABLE 10.3 Average Relative Sm2 Rates for Some Alkyl Substrates... 

The reactions in this chapter are classified according to the attacking atom of the nucleophile in the order O, S, N, halogen, H, C. For a given nucleophile, reactions are classified by the substrate and leaving group, with alkyl substrates usually considered before acyl ones. Nucleophilic substitutions at a sulfur atom are treated at the end. 

Vinyl halides (example 17, Table VII) were first observed by Kroper to form acrylic esters by reaction with carbon monoxide under pressure and tetracarbonylnickel in methanol at 100°C. These reactions were later shown to occur under much milder conditions. Highly stereospecific reactions were observed c/s-vinyl halides gave cis-carbonylation products and trans-vinyl halides trans-carbonylation products (example 18, Table VII). Retention of configuration of alkyl substrates in carbonylation seems to be a general feature in carbon monoxide chemistry (193a). 

C). The substrate is deprotonated [pK(PhCH2COOMe) 22.7] and trapped by an alkyliodide (—78°C). This procedure leads selectively to mono a-alkylation (81-99%) [103]. Selective monoalkylation of 8-diketones in 70 to 95% yield was obtained by a similar procedure, and only in a few cases (bulky secondary alkylhalides) were the O-alkylated substrate found as a side product. Tetraalky-lammonium counter cations were necessary in stabilizing the enolate Na+ counter cations did not give selective C-alkylation [104]. 

Alkyl azides are conveniently prepared from the reaction of alkali metal azides with an alkyl halide, tosylate, mesylate, nitrate ester or any other alkyl derivative containing a good leaving group. Reactions usually work well for primary and secondary alkyl substrates and are best conducted in polar aprotic solvents like DMF and DMSO. The synthesis and chemistry of azido compounds is the subject of a functional group series. ... 

Lithiation of 2-biphenylcyclohexanone gave two enolate species in THF one an unconjugated secondary enolate and the other a conjugated tertiary enolate. The former exists dominantly as the tetramer and the latter as a monomer-dimer mixture. In both cases the monomer reacts faster than the aggregates with alkylating substrates. ... 

By coupling of allyl -I- alkyl substrates N,N-Methylphenylaminotributyl-phosphonium iodide, 191 3-Methyl-3-(phenylthio)-l-butene,... 

In the carbanionic mechanisms for elimination, if the substrate has two proton-bearing ft carbons, the more acidic protons will be removed. Thus in alkylated substrates the double bond will be oriented toward the less substituted carbon and Hofmann elimination is obtained. 

Rueter et al.62 described an efficient and clean synthesis of diethyl-(2-/ -tolyl-ethyl)amine (30) from 2-p-tolylethanol and diethylamine by making use of the benzenesulfonyl chloride resin (26) to catch the intermediate O-alkylated substrate (31) followed by the release (from the intermediate resin) of the final product (30) upon treatment with diethylamine (Fig. 12). 

Since Corey s group first reported 0(9)-allyl-N-(9-anthracenylmethyl) cinchonidi-nium bromide as a new phase-transfer catalyst [13], its application to various asymmetric reactions has been investigated. In particular, this catalyst represents a powerful tool in various conjugated additions using chalcone derivatives (Scheme 3.2). For example, nitromethane [14], acetophenone [15], and silyl eno-lates [16] produce the corresponding adducts in high enantioselectivity. When p-alkyl substrates are used under PTC conditions, asymmetric dimerization triggered by the abstraction of a y-proton proceeds smoothly, with up to 98% ee [17]. 

Table 4.1. Average relative rates for Sn2 reactions of alkyl substrates RX [1, 92, 93],...

The benzene sulfonyl group is used as a transfer of activation reagent to alkylate selectively the N-H of both 7//-pyrrolo[2,3-fl pyrimidines 174 and 5-aminoindole substituted on thienopyrimidines 175 (Equations 31 and 32). A variety of primary and secondary alcohols are utilized as alkylating substrates <1998TL5685>. 

Nearly all types of C-Mannich bases deriving from activated alkyl substrates (Table... 

When trialkylphosphites are treated with fluoroalkanoyl chlorides, perhalogenated fluoro-alkenes, perfluorinated aromatics, and other fluorinated alkylating substrates, an Arbuzov reaction takes place and alkyl fluorides are formed as byproducts. The method has been used to prepare 6-fluoro-6-deoxy-l,2 3,4-di-f7-isopropylidenegalactose (1). ... 

An extremely useful variant of Suzuki reaction uses B-alkyl substrates with aryl or vinyl halides. The B-alkyls are prepared by hydroboration of an alkene with 9-BBN-H. With appropriate palladium ligands, reductive... 

The diastereoselectivity of the reaction is lower than that obtained in benzylations of pseudoephedrine amide enolates lacking the a-hydroxyl group. Although an extensive series of 0-protected derivatives of a-hydroxyacetamide has been examined in a search for an alternative alkylation substrate [TBS, TBDPS, THP, Bn, BOM, Piv, and methy 1( 1 -methoxyethyl)], none has provided satisfactory results nor offered any improvement over pseudoephedrine a-hydroxyacetamide itself. ... 

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