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Ferf-Butoxide, nucleophilicity

Nucleophilic displacement of bromide from 5-acetyl-10-bromo-5//-dibenz[7>,/]azepine (41) by alkoxide,132 and by cyanide ion in dimethylformamide,212 has been noted. However, replacement of bromide by cycloalkylamines (e.g., piperidine) to give the 10-cycloalkylamino derivatives. e.g. 44, is best accomplished in the presence of potassium ferf-butoxide, a result which suggests that the aminodebromination proceeds via an elimination-addition (EA) pathway involving an azepyne intermediate 43 (see Section 3.2.1.5.7.) rather than by the more usual addition-elimination (AF.) mechanism.118... [Pg.271]

The polymerization of lactones is initiated by nucleophilic metal alkoxides. It is worth noting that bulky alkoxides are not nucleophilic enough and react as bases. For example, potassium ferf-butoxide deprotonates (3-propionolactone and sCL into new anionic species, which are anionic initiators for the polymerization of lactones [8] (Fig. 4). As a rule, carboxylic salts are less nucleophilic than the corresponding alkoxides and are, in general, not efficient initiators for the polymerization of lactones. Nevertheless, (3-lactones are exceptions because their polymerization can be initiated by carboxylic salts [8]. [Pg.179]

As a practical matter, elimination can always be made to occur quantitatively. Strong bases, especially bulky ones such as ferf-butoxide ion, react even with primary alkyl halides by an E2 process at elevated temperatures. The more difficult task is to find conditions that promote substitution. In general, the best approach is to choose conditions that favor the SN2 mechanism—an unhindered substrate, a good nucleophile that is not strongly basic, and the lowest practical temperature consistent with reasonable reaction rates. [Pg.357]

The nucleophilic addition of the a-lithiated alkyldiphenylphosphine oxide B to the carbonyl group of an aldehyde at the beginning of a Wittig-Horner reaction results in the phos-phorylated lithium alkoxide D. If the alkene synthesis is carried out in a single step, the Li of the intermediate D is, without workup, reversibly replaced by K by adding potassium-ferf-butoxide. In this way, the phosphorylated potassium alkoxide F is made available. Only in F... [Pg.468]

To serve as a nucleophile, an ion or molecule must get in close to a carbon atom to attack it. Bulky groups on the nucleophile hinder this close approach, and they slow the reaction rate. For example, the ferf-butoxide ion is a stronger base (for abstracting protons) than ethoxide ion, but terf-butoxide ion has three methyl groups that hinder any close approach to a more crowded carbon atom. Therefore, ethoxide ion is a stronger nucleophile than fert-butoxide ion. When bulky groups interfere with a reaction by virtue of their size, we call the effect steric hindrance. [Pg.238]

In their search for the optimal base for the selective formation of 139, the authors unexpectedly found a different reaction product, namely 142 (nine examples, 38-75% yield). This product is formed when a nucleophilic base such as sodium ethoxide or potassium ferf-butoxide was used instead of NEts (under otherwise identical reaction conditions as for the formation of 139). The formation of 142 is explained by nucleophilic attack of ethoxide or ferf-butoxide to intermediate 138 followed by a ring-opening/recyclization. [Pg.118]

For example, although p a tables indicate that fert-butoxide [(CH3)3CO ] is a stronger base than ethoxide (CH3CH20 ), ethoxide is the stronger nucleophile. The three CH3 groups around the O atom of ferf-butoxide create steric hindrance, making it more difficult for this big, bulky base to attack a tetravalent carbon atom. [Pg.241]

However, the four rules given above do not always hold. One reason is that steric influences often play a part. For example, the ferf-butoxide ion Me3CO is a stronger base than OH or OEt, but a much poorer nucleophile because its large bulk hinders it from closely approaching a substrate. [Pg.493]

Alkali metal salts with nucleophilic anions are notably good initiators for chloral anionic polymerization (Fig. 26). The most studied initiator is lithium ferf-butoxide. When 0.2 mole % of lithium ferf-butoxide (based on chloral) was added to neat chloral monomer at 60°C the alkoxide (CH3)3C0CH(CCl3)0 Li was formed instantaneously, but no further addition of chloral occurred. This reaction was observed by an NMR study of the system and confirmed by the chemical reactions of the product alkoxide, which acted as the initiator. Tertiary amines such as pyridine and NR3 where R is an alkyl group have been found to be good initiators for chloral polymerization. They are slower initiators than lithium... [Pg.372]

Dibromocarbene undergoes addition to the more substituted (more nucleophilic) double bond of unconjugated di- and polyenes di- and polyadducts may also be obtained, particularly using the bromoform/base/phase-transfer catalyst method. For the preparation of monoadducts, using an excess of diene possessing equivalent double bonds, bromoform and base/phase-transfer catalyst or potassium ferf-butoxide are recommended. The examples l,34 235 3,35,36 and 435 are typical. [Pg.709]

Steric effects, on the other hand, do affect nucleophilicity. A bulky nucleophile cannot approach the back side of a carbon as easily as a less sterically hindered nucleophile can. Thus, the bulky ferf-butoxide ion, with its three methyl groups, is a poorer nucleophile than ethoxide ion even though ferf-butoxide ion is a stronger base. [Pg.371]

A secondary alkyl halide can form both substitution and elimination products under Sn2/E2 conditions. The relative amounts of the two products depend on the base strength and the bulk of the nucleophile/base. The stronger and bulkier the base, the greater the percentage of the elimination product. For example, acetic acid is a stronger acid = 4.76) than ethanol (pA a = 15.9), which means that acetate ion is a weaker base than ethoxide ion. The elimination product is the main product formed from the reaction of 2-chloropropane with the strongly basic ethoxide ion, whereas no elimination product is formed with the weakly basic acetate ion. The percentage of elimination product produced would be increased further if the bulky ferf-butoxide ion were used instead of ethoxide ion (Section 10.3). [Pg.423]

Because the pKa of p-methoxyphenol allows a full deprotonation by potassium ferf-butoxide, it is suggested that the propagation results from nucleophilic attack of the phenoxide on an intermediate quinodimethane formed by dehydrohalogenation of the monomer. Polymerization under these conditions is found to yield polymers with very low polydispersity values. ... [Pg.99]

Aromatic Annulation. 7-Methoxy-3-(phenylsulfonyl)-l(3Y/)-isobenzofuranone (1) can be deprotonated at —78 °C with either lithium diisopropylamide or lithium ferf-butoxide to form a soluble yellow anion which can be utilized as an effective nucleophile in the Michael reaction. The initial anionic adduct cyclizes with concomitant elimination of benzenesulfinic acid to yield a 1,4-dihydroxynaphthalene which is unambiguously disubstituted at the 2- and 3-positions (eq l). ... [Pg.361]

With larger, sterically hindered bases such as ferf-butoxide, however, where isomeric alkenes are possible, the major product is often the less substituted alkene because reaction occurs primarily at the most accessible H atom. Sterically hindered bases such as fert-butoxide are also noteworthy because the steric hindrance prevents them from reacting as nucleophiles, even with primary alkyl halides. [Pg.403]

Formation of 2,3-anhydro compound 52 (IS [2,0-3]) in the course of a triflate displacement (entry 19 [49]). Under the conditions cited, the anhydro ring formation was not observed with the corresponding )3-anomer (entry 20), but occurred with both anomers almost exclusively when ferf-butoxide in tert-butyl alcohol (or TBAF in toluene) was applied. As a corollary, excellent yields of Sn2 products were obtained, again with both anomers, in reactions with good nucleophiles (e.g. azide in DMF). [Pg.226]

This is a typical nucleophilic acyl substitution reaction, with the amine of the amino acid as the nucleophile and ferfr-butyl carbonate as the leaving group. The terf-butyl carbonate then loses CO2 and gives ferf-butoxide, which is protonated. [Pg.1313]

Bulky groups adjacent to the nucleophilic atom reduce the reactivity of a nucleophile because these groups hinder the approach of the nucleophile toward the electrophilic atom. For example, consider the relative reactivities of the methoxide and ferf-butoxide ions ... [Pg.1282]


See other pages where Ferf-Butoxide, nucleophilicity is mentioned: [Pg.234]    [Pg.25]    [Pg.203]    [Pg.203]    [Pg.238]    [Pg.127]    [Pg.242]    [Pg.25]    [Pg.927]    [Pg.225]    [Pg.54]    [Pg.62]    [Pg.212]    [Pg.713]    [Pg.425]    [Pg.165]    [Pg.193]    [Pg.244]    [Pg.297]    [Pg.297]    [Pg.216]    [Pg.816]   
See also in sourсe #XX -- [ Pg.239 ]




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Ferf-Butoxide

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