Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Alkynes organolithiums

Alkynic ketones have been used extensively in natural product synthesis, due in large part to the contributions of Midland and coworkers and the development of generd methods for enantioselective reduction of this moiety to afford optically active propargyl alcohols using chiral trialkylboranes. Furthermore, the derived alkynic alcohol is a versatile system which can be manipulated directly into cis-or rra 5-allylic alcohols and as a precursor for vinylorganometallic species. This section will briefly cover progress made in the direct acylation of alkynic organolithiums with the acylation protocol d veloped by Weinreb (see also Section 1.13.2.7). [Pg.405]

G.ii. Intramolecular Addition to Alkenes and Alkynes. Organolithium reagents can react with alkenes or alkynes in an intramolecular reaction, although both are relatively inert to the analogous intermolecular reaction. Ward treated alkynyl bromide 263 with n-butyllithium and observed a 60% yield of... [Pg.622]

These compounds are sources of the nucleophilic anion RC=C and their reaction with primary alkyl halides provides an effective synthesis of alkynes (Section 9 6) The nucleophilicity of acetylide anions is also evident m their reactions with aldehydes and ketones which are entirely analogous to those of Grignard and organolithium reagents... [Pg.597]

The reaction of tnfluoromethyl-substituted A -acyl umnes toward nucleophiles in many aspects parallels that of the parent polyfluoro ketones Heteronucleophiles and carbon nucleophiles, such as enarmnes [37, 38], enol ethers [38, 39, 40], hydrogen cyanide [34], tnmethylsilylcarbomlnle [2,47], alkynes [42], electron-nch heterocycles [43], 1,3-dicarbonyl compounds [44], organolithium compounds [45, 46, 47, 48], and Gngnard compounds [49,50], readily undergo hydroxyalkylation with hexafluoroace-tone and amidoalkylation with acyl imines denved from hexafluoroacetone... [Pg.842]

The analogous dimerization of alkynes over Fe(C0)5 is not applicable, so clearly a different route towards alkynylated derivatives of 25 was needed. Comparison of 25 to cymantrene suggests that metallation of the hydrocarbon ligand should be the route of choice for the synthesis of novel substituted cyclobutadienes. In the literature, addition of organolithium bases (MeLi, BuLi) to the CO ligands with concomitant rearrangement had been observed [25]. But the utilization of LiTMP (lithium tetramethylpiperidide, Hafner [26]) or sec-BuLi as effectively non-nucleophilic bases led to clean deprotonation of the cyclobuta-... [Pg.137]

Organolithium reagents have also been employed for the synthesis of novel bis(alkynyl)mercury derivatives. These include Hg(C=CCF3)263 and 46-48,64 which have been synthesized along with the bis(alkynyl)aurate analogs. Bis(alkynyl)mercury species such as 49 can also be obtained by reaction of monosubstituted alkynes with K2[Hgl4] in basic aqueous solutions.6 ... [Pg.426]

Organolithium reagents47 instead of organoaluminum derivatives48, 9 have been used for the carbometallation of unactivated alkynes under iron catalysis (Scheme 9). Thus, variously substituted alkynes 30 and 32, bearing a tertiary... [Pg.303]

Standard organolithium reagents such as butyllithium, ec-butyllithium or tert-butyllithium deprotonate rapidly, if not instantaneously, the relatively acidic hydrocarbons of the 1,4-diene, diaryhnethane, triarylmethane, fluorene, indene and cyclopentadiene families and all terminal acetylenes (1-alkynes) as well. Butyllithium alone is ineffective toward toluene but its coordination complex with A/ ,A/ ,iV, iV-tetramethylethylenediamine does produce benzyllithium in high yield when heated to 80 To introduce metal into less reactive hydrocarbons one has either to rely on neighboring group-assistance or to employ so-called superbases. [Pg.457]

The electrophile for the cyclization reaction of an a-amino-organolithium compound is not restricted to a terminal (or phenylthio-substituted) ahcene and examples have been reported using carboxylic amides, alkynes and allyhc ethers." " For example, Fautens and Kumanovic reported that treatment of the bicyclic stannane shown in Scheme 24... [Pg.1018]

Terminal alkynes are acidic, and the end hydrogen can be removed as a proton by strong bases (e.g. organolithiums, Grignard reagents and NaNH2) to form metal acetylides and alkynides. They are strong nucleophiles and bases, and are protonated in the presence of water and acids. Therefore, metal acetylides and alkynides must be protected from water and acids. [Pg.109]

It was observed that the metallation of terminal alkynes by organomagnesium (or organolithium) reagents considerably accelerated the rate of the subsequent addition of allylzinc bromide. The products resulting from a bis-addition predominate even in the case of sterically more demanding alkynes (equation 140). [Pg.938]

Alkali metal alkyls, particularly n-butyl lithium, are the most frequently used reagents to form metallated intermediates.246 247 In certain cases (di- and triphenyl-methane, acetylene and 1-alkynes, cyclopentadiene) alkali metals can be directly applied. Grignard reagents are used to form magnesium acetylides and cyclopenta-dienyl complexes.248 Organolithium compounds with a bulky alkoxide, most notably M-BuLi-ferf-BuOK in THF/hexane mixture, known as the Lochmann-Schlosser reagent or LICKOR superbase, are more active and versatile reagents.249-252... [Pg.250]

Alkynes, and Arenes, 1985 Paul N. Rylander, Hydrogenation Methods, 1985 Ernest W. Colvin, Silicon Reagents in Organic Synthesis, 1988 Andrew Pelter, Keith Smith and Herbert C. Brown, Borane Reagents, 1988 Basil Wakefield, Organolithium Methods, 1988... [Pg.1]

Non-aromatic organolithium compounds can be prepared by transmetallation of resin-bound stannanes [25] or by deprotonation of alkynes [26], triphenylmethane [27], or other resin-bound C II acidic compounds with lithium amides or similar bases (Figure 4.3). The reaction of polystyrene-bound trialkylboranes with diethylzinc yields resin-bound alkylzinc derivatives [28]. [Pg.162]

The reacuons of electrophihc tnflyl sources with nucleophiles were investi gated The reaction of tnfhc anhydride with an organolithium reagent is not synthetically promising because of ditnflylation and other side reactions [20] When phenyllithium reacts with tnfhc anhydnde, dimerization products and acetylenic Michael diadducts are observed [20] (equation 17), but using the sodium salt of the alkynes instead of the lithium salt provides the alkynyl tnfluoromethyl sulfones [21] (equation 18) (Table 7) Alkynyl tnfluoromethyl sulfones are of synthetic interest, because they show a pronounced reactivity toward nucleophiles in addition reactions and cyclopentadiene in Diels-Alder reactions [21] (Table 7)... [Pg.565]

Due to its high ionic character, the carbon-lithium bond is very reactive and adds under mild conditions to ethylene or dienes and under more severe conditions to other alkenes. Some functionalized alkenes can be used, and high regio- and stereo-selectivity is usually observed in these carbolithiation reactions, especially if a precoordination of the lithium organometallic with the alkene is possible. Intramolecular carbolithiations of alkenes proceed under mild conditions and allow the preparation of several stereochemically well defined mono- and bi-cyclic compounds. Alkynes are too reactive, and can lead, with organolithium derivatives, to several side reactions, and seldom afford the desired carbolithiated product in good yield. [Pg.867]

Acyliron complexes have found many applications in organic synthesis [40]. Usually they are prepared by acylation of [CpFe(CO)2] with acyl chlorides or mixed anhydrides (Scheme 1.13). This procedure affords alkyl, aryl and a,P-unsaturated acyliron complexes. Alternatively, acyliron complexes can be obtained by treatment of [Fe(C5Me5)(CO)4]+ with organolithium reagents, a,P-Unsaturated acyliron complexes can be obtained by reaction of the same reagent with 2-alkyn-l-ols. Deprotonation of acyliron complexes with butyllithium generates the corresponding enolates, which can be functionalized by reaction with various electrophiles [40]. [Pg.9]

The hydroamination of alkynes is an efficient way to obtain aldimines with the advantage of avoiding formation of by-products. As shown in Scheme 8.65, the method has been developed into a multicomponent synthesis of a-branched amines. Aldimines 154 are formed using a titanium derivative as catalyst and reacted in situ with an organolithium reagent [141]. [Pg.261]


See other pages where Alkynes organolithiums is mentioned: [Pg.405]    [Pg.405]    [Pg.565]    [Pg.594]    [Pg.1025]    [Pg.18]    [Pg.353]    [Pg.60]    [Pg.44]    [Pg.74]    [Pg.72]    [Pg.302]    [Pg.902]    [Pg.591]    [Pg.601]    [Pg.129]    [Pg.308]    [Pg.166]    [Pg.70]    [Pg.85]    [Pg.128]    [Pg.140]    [Pg.872]    [Pg.89]    [Pg.1116]    [Pg.171]   
See also in sourсe #XX -- [ Pg.2 , Pg.3 , Pg.4 , Pg.5 ]

See also in sourсe #XX -- [ Pg.2 , Pg.3 , Pg.4 , Pg.5 , Pg.11 ]




SEARCH



Alkynes, reaction with organolithium reagents

Organolithium reagents, addition alkynes

© 2024 chempedia.info