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Hydrozirconation 1 -alkynes

Schwartz s reagent, ZrHClCp2 n (Figure 2.29b), readily (and often regioselectively) hydrozirconates alkynes to provide o-vinyl complexes from which the vinyl ligand may be cleaved by a wide range of electrophiles, in a manner reminiscent of hydroboration chemistry (Figure 4.15). [Pg.76]

The alkenylzirconium 685, prepared by hydrozirconation of a terminal alkyne with hydrozirconocene chloride, reacts with alkenyl halide to afford the conjugated diene 686(545]. The Zr reagent can be used even in the presence of the carbonyl group in 687, which is sensitive to Al and Mg reagents. [Pg.228]

AUylzirconium complexes are conveniently obtained by the regio- and stereoselective hydrozirconation of allene [127-133] and can be, for example, used subsequently for the MAO-catalyzed allylzirconation of alkynes to prepare enyne derivatives [132]. Alternatively, the preparation of (E)-l,3-dienes from aldehydes and the appropriate allylstannane zirconocene derivative (R = SnBu,) is accomplished (Scheme 8-17) [131], Note that addition of [Cp2Zr(H)Cl[n (1) on the aUenyl reagent with the... [Pg.263]

The hydrozirconation reaction of alkynes tolerates the presence of a large variety of functional groups. As a consequence, this protocol has become very popular in organic synthesis [135-142]. [Pg.264]

Hydrozirconation of terminal alkynes R-C=CH (R= aryl, alkyl) with 1 affords terminally ( )-Zr-substituted alkenes with high efficiency and excellent stereochemical and regiochemical control (>98%). These alkenylzirconocene complexes are of particular interest for synthetic use [136, 143, 144]. Moreover, beside the electropositive halogen sources [145] and heteroatom electrophiles [3] used in the pioneering studies to directly cleave the Zr-C bond, ( )-vinyl-Zr complexes were recently transformed into a number of other trans-functionalized alkenes such as ( )-vinyl-sul-fides[146], vinylic selenol esters [147], vinyl-sulfones [148], vinyl-iodonium [149], vinyl-(R0)2P(0) [150], and vinilic tellurides [143]. [Pg.264]

Terminal heterosubstituted alkynes X-C=CH such as RO-C=CH [16, 17, 151-153], RSe-teCH (R= alkyl, aryl) [154-157], MejSi-teCH [158] and R P-feCH [159] were regioselectively converted into the ( )-2-ethenylzirconium complexes via hydrozirconation using 1. In marked contrast, with terminal BuTe-C=CH [154]... [Pg.264]

Scheme 8-18 Regio- and stereo-selectivity in hydrozirconation of terminal alkynes... Scheme 8-18 Regio- and stereo-selectivity in hydrozirconation of terminal alkynes...
As for alkenes, the rate of hydrozirconation of alkynes decreases with increasing substitution on the alkyne. An unsymmetrical diyne reacts with 1 preferentially at the less-substituted triple bond [85]. [Pg.265]

The chemoselectivity of Schwartz s reagent (1) toward alkynes, alkenes, nitriles, and carbonyl groups, and thus its general functional group compatibility, can be modulated. However, it is important to keep in mind that the presence of functional groups may have regiochemical consequences on the hydrozirconation reaction. [Pg.269]

As predicted from the comparative rates for C=C over C=C hydrozirconation cited earlier, a (poly)enyne is selectively hydrozirconated at the alkyne moiety, whatever the position of the alkene function [138, 210] in the molecule. It can be exempUfied by the chemoselective hydrozirconation of 1,3-butenyne. One exception to this chemoselectivity has been reported, which showed the terminal alkene to react with 1 but leaving the TMS-substituted alkyne function intact (Scheme 8-25). [Pg.269]

The synthetic potential of alkenylzirconium complexes is partially due to the fact that the hydrozirconation of alkynes can be carried out in the presence of some synthetically useful functional groups such as halide [80,153, 211, 212], acetals, amides, imides, carbamates, sulfides [186], ester, cyano [95, 213] and chiral propargyl amino functionalities [214]. [Pg.269]

Nitriles [153, 211] are tolerated by an equivalent of reagent in the presence of a particularly reactive site of unsaturation, such as a terminal alkyne or vinyl function, whereas methacrylonitrile gives only C N hydrozirconation (Scheme 8-26) [215]. [Pg.269]

Carboxylic acids can be protected as oxazolines [96, 105-107, 186, 191] or as ester functions. Alkynic esters such as silyl esters [153, 211], tert-butyl esters [216], and even benzyl esters [153, 211] have been successfully hydrozirconated when the reactive site was a terminal alkyne or vinyl group (Scheme 8-27). [Pg.270]

Some hydrometalation reactions have been shown to be catalyzed by zirconocene. For instance, CpiZrCf-catalyzed hydroaluminations of alkenes [238] and alkynes [239] with BU3AI have been observed (Scheme 8-34). With alkyl-substituted internal alkynes the process is complicated by double bond migration, and with terminal alkynes double hydrometalation is observed. The reaction with "PrjAl and Cp2ZrCl2 gives simultaneously hydrometalation and C-H activation. Cp2ZrCl2/ BuIi-cat-alyzed hydrosilation of acyclic alkenes [64, 240] was also reported to involve hydrogen transfer via hydrozirconation. [Pg.273]

Despite the great success of the transmetalation process in the enantiose-lective arylation of ketones, its extension to allylation or alkynylation reactions failed, providing the corresponding tertiary alcohols with enantiomeric excesses never higher than 50% ee. On the other hand, more success has been found in the alkenylation of ketones. The process started with the hydrozirconation of terminal alkynes to give the corresponding alkenylzirconium intermediates, which were transmetalated by reaction, in this case, with various ketones in the presence of the HOCSAC ligand. This protocol tolerated the presence of other carbon-carbon multiple bonds on the alkyne, as well as different functionalities and achieved excellent results for alkyl ketones, a,(3-unsaturated ketones and even dialkylketones, as shown in Scheme 4.22. [Pg.172]

Derivatives of zirconium with a Zr-H bond also can add to alkenes and alkynes. This reaction is known as hydrozirconation.230 The reagent that is used most frequently... [Pg.356]

Another type of mixed cyanocuprate has both methyl and alkenyl groups attached to copper. Interestingly, these reagents selectively transfer the alkenyl group in conjugate addition reactions.16 These reagents can be prepared from alkynes via hydrozirconation, followed by metal-metal exchange.17... [Pg.679]

Scheme 25 Hydroboration and hydrozirconation strategies for aldehyde/alkyne reductive coupling... Scheme 25 Hydroboration and hydrozirconation strategies for aldehyde/alkyne reductive coupling...
As Scheme 16 shows, vinyl(methyl)zinc compounds 17 were obtained from the hydrozirconation of terminal alkynes with Cp2ZrHGl, followed by treatment with dimethylzinc. The initially formed vinyl zirconium complex undergoes rapid transmetallation with ZnMe2 to yield the product.44... [Pg.323]

A highly creative method for ZnMe2-mediated addition reactions of alkenylzirconocenes to aldimines was recently proposed by the Wipf group.345,346 The protocol includes a three-step sequence (i) alkyne hydrozirconation,... [Pg.398]

It was shown (654) that the sequence terminal alkyne hydrozirconation, Zr to Zn exchange and addition to nitrones, is a good method to the stereoselective synthesis of (E)-N-allylhydroxylamines, under mild conditions and in good yield. [Pg.280]

Monosubstituted alkenes and certain alkynes can undergo hydroalumination with iBujAl in the presence of a catalytic amount of Cp2ZrCl2, providing a convenient alternative to hydrozirconation [75]. [Pg.11]


See other pages where Hydrozirconation 1 -alkynes is mentioned: [Pg.325]    [Pg.35]    [Pg.789]    [Pg.50]    [Pg.256]    [Pg.264]    [Pg.264]    [Pg.265]    [Pg.265]    [Pg.265]    [Pg.143]    [Pg.144]    [Pg.357]    [Pg.483]    [Pg.321]    [Pg.131]    [Pg.136]    [Pg.138]    [Pg.10]   
See also in sourсe #XX -- [ Pg.262 ]

See also in sourсe #XX -- [ Pg.262 ]




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Esters, alkynic hydrozirconation

Hydrozirconation

Hydrozirconation of Internal Alkynes

Hydrozirconation of Terminal Alkynes

Hydrozirconation of alkynes

Hydrozirconation of an alkyne

Hydrozirconation terminal alkynes

Hydrozirconations of alkynes

Zirconium, chlorobis hydrozirconation of alkynes with

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