Barbier-type reactions

Reisse used activated zinc for aqueous Barbier-type reactions.66 Submicromic zinc powder produced by pulsed sono-electroreduction is about three times more effective than the commercial variety. The stereochemical course of the allylation and propargylation of several aldehydes with crotyl and propenyl halides using zinc powder as the... 

Samarium-mediated Barbier-type reactions of carbonyl compounds were reported in a similar reaction system (Equation (6)).22 THF is the key solvent to obtain the product 33. In MeOH, pinacol coupling-type reaction proceeded predominantly, while the reaction failed to produce any desired compound in CH3CN.23... 

Additionally, various intra- and intermolecular iron-catalyzed Barbier-type reactions of organosamarium com-pounds and carbonyl electrophiles have been reported by Molander and co-workers. 

The combination of Sml2 and HMPT effects a Barbier-type reaction of w-bromo esters with carbonyl compounds to provide y- and 8-lactones (equation I).14... 

Scheme 168 Samarium-mediated Barbier-type reaction of carbonyl compounds with allyl halides.

The same polymeric arenes that served as metallation catalysts in equation 119 can also be used for silylation in Barbier-type reactions (equation 131). The polymer is presumably converted to a lithium arene adduct that activates metallic lithium for metallation of the halogenated substrates, before addition of an electrophile to achieve the synthetic goal. Equations 132-135 illustrate some of the cases investigated. The products can be characterized by the usual spectroscopic methods . 

The use of substoichiometric amounts of an arene (naphthalene or biphenyl) was first studied in the reaction of bromobenzene and benzaldehyde with sodium, under Barbier-type reaction conditions The possibility of using a substoichiometric amount of DTBB... 

Barbier-type reaction conditions ) in THF at —30°C (—78°C for phenylacetonitrile) yielding, after hydrolysis, the expected compounds 20 (Scheme 8) . ... 

Thus, chloro enamines 113, either under Barbier-type reaction conditions (—40 °C) or in a two-step process (hthiation at —90 °C and Sg reaction at —90 to —40 °C), were lithiated with DTBB (5%) and finally hydrolyzed, after condensation with different electrophiles, giving the expected functionalized enamines 114 (Scheme 44) °. ... 

Functionalized propargyUc organolithium compounds are probably involved in the transformation of chlorinated ethers or amines 211 into polyfunctionalized products 212, which were achieved through a DTBB-catalyzed lithiation under Barbier-type reaction conditions (Scheme 73). The reaction failed for the corresponding thioethers (Y =... 

Barbier-type reaction conditions) to yield, after hydrolysis with phosphate buffer and final esterification with methanol under PTSA catalysis, the corresponding functionalized methyl esters 229 (Scheme 77) . 

The Barbier-type reaction shown in Scheme 121 was also applied to the dichlorinated materials 432-434, as well as trichloroaUcanes 435 and even tetrachloromethane 436. In every case, all chlorine atoms were replaced by electrophilic fragments, so the starting material behaved as polylithium synthons. Actually, the whole process takes place probably by successive tandem lithiation-SE reactions until consumption of all chlorine atoms... 

In the case of chlorobenzyl chlorides 504, the same process had to be performed under Barbier-type reaction conditions. These dichlorinated materials 504 were lithiated with DTBB in a catalytic amount (4%) in the presence of different electrophiles to give, after final hydrolysis with water, the corresponding difunctionalized products 505 (Scheme 141) ". ... 

Benzamides 565 without any substituent at the para position reacted with lithium and a catalytic amount of naphthalene under Barbier-type reaction conditions (in the presence of a carbonyl compound) in THF at —78 °C to give, after hydrolysis, the corresponding dearomatized products 566 (Scheme 151). When 567 was used as starting material with a 4-ferf-butyl group in p-position, and using 3-pentanone as electrophile and under the same reaction conditions, the fraw -product 568 was the only one isolated . 

TABLE 13. Barbier-type reaction of iodopyrimidine derivative with aldehyde... 

Indium-promoted organometallic reactions are greatly accelerated in water, especially when the coreactant carbonyl compound also has good water solubility. Otherwise, aqueous tetrahydrofuran can be used. To date, indium is the most effective metal for promoting Barbier-type reactions under aqueous conditions. As illustrated here, this is of particular value where formaldehyde is concerned, since the need to generate monomeric formaldehyde by thermal cracking is avoided. 

Barbier-type reactions of alkyl iodides with ketones can be performed with Sml2 when Fe(III) compounds are used as catalysts [22]. Particularly efficient for the intramolecular reaction of co-iodo ketones such as compound 16 turned out to be Fe(dbm)3 (dbm = l,3-diphenyl-l,3-propanedionato). The latter is an air-stable, THF-soluble, non-hygroscopic complex that can be very easily prepared from... 

In analogy with iron-catalyzed Barbier-type reactions with Sml2 (cf. Scheme 8.5), intramolecular nucleophilic acyl substitutions (SNt) can be used to prepare cyclic ketones from esters [50]. An illustrative example is shown in Scheme 8.13 [51], Again, tris(l,3-diphenyl-l,3-propanedionato)iron(III) [Fe(dbm)3] is used as the catalyst. Compound 40 is obtained as one racemic diastereoisomer. 

Barbier-type reactions, 9, 358 catalystic asymmetric reactions, 9, 359 Lewis acid-promoted reactions, 9, 358 Allenyltrichlorosilanes from 1,3-enynes, 9, 309 preparation, 9, 309... 

Bacteria, antimicrobials against, 12, 456 Baeyer-Villiger oxidation, via tin amides, 9, 370 Barbier-Grignard-type reactions, and sonochemical metal insertions, 1, 315 Barbier-type reactions allenyl and propargyl tins, 9, 358 with allylic tins, 9, 357 with antimony(III) compounds, 9, 426 with bismuth(III) compounds, 9, 433 with cerium reagents, 10, 409 with indium compounds, 9, 685... 

Barbier-type reactions, 9, 433 in catalyzed C-C bond formation, 9, 438 in C-C bond formations, 9, 435 in C-heteroatom bond formations, 9, 440 with copper catalysts, 9, 442 non-catalyzed reactions, 9, 443 miscellaneous reactions, 9, 444 in oxidations, 9, 443 in reduction reactions, 9, 444 Bismuth(V) compounds... 

Organopalladium complexes do usually not transfer a formal carbanion to aldehydes or ketones, but intramolecular Barbier-type reactions of this kind have been observed (Scheme8.2). 

In many cases, activation of the zinc dust is necessary to reach complete conversion or to accelerate the reaction. This activation can be achieved by treatment of zinc dust with an acid chloride267 but can be achieved also with liquid ammonia268 or by sonoelectrochemical methods.259,269,269a Activation can be achieved by adding metallic salts such as AICI3, CeCb, PbBr2, or Cul to the reaction mixture.2536,257,270 Sonication proved also to enhance the reactivity of Barbier-type reaction in aqueous media (Equation (157)).2S3 255 2S6 270 270a 271... 

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