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Enantioselective addition of terminal alkynes

The asymmetric addition of different types of nucleophiles at the C-l position of 3,4-dihydroisoquinolines were highlighted in a number of publications. Schreiber et al. described an enantioselective addition of terminal alkynes 136 to 3,4-dihydroisoquinolinium bromide 137 in the presence of triethylamine, catalytic copper bromide, and QUINAP <06OL143>. The resulting 1-substituted tetrahydroquinolines 138 were isolated in high yield and high enantiomeric excess in most cases. [Pg.332]

Carreira and co-workers developed a highly efficient enantioselective addition of terminal alkynes to aldehydes giving propargyl alcohols by the mediation of zinc tri-flate and N-methylephedrine [17]. This reaction serves as a convenient and powerful synthetic route to a wide variety of enantioenriched allenes via propargyl alcohols. Dieter and Yu applied this alkynylation to the asymmetric synthesis of allenes (Scheme 4.12) [18]. Reaction of phenylacetylene with isobutyraldehyde afforded the propargyl alcohol in 80% yield with 99% ee, which was mesylated to 49 in quantitative yield. Reaction of 49 with the cyanocuprate 50 afforded the desired allene 51 with 83% ee. [Pg.147]

Recent Developments in Enantioselective Addition of Terminal Alkynes to Aldehydes... [Pg.32]

Cozzi achieved the first general catalytic enantioselective addition of terminal alkynes to unactivated ketones (Scheme 4.42) [37]. To overcome the low reactivity of the ketone substrates, the catalytic methodology involves the concept of the double activation of Lewis acid-Lewis base, and especially the use of salen-Zn(II) complexes (122). For a range of aromatic and aliphatic ketones, 20mol% of (R,R)-N,N -bis(3,5-di-tert-butylsalicylidene)-l,2-cyclohexanediamine (121) in toluene room temperature effectively provides the adduct products (120) with moderate to high enantioselectivities. [Pg.162]

Addition of lithiated alkoxy ethynyl anion with chiral Al-sulfinyl imines proceeds with dr >95 5, which can be reversed in the presence of BF3. Excellent diastereoselec-tivity has been reported for zinc-mediated addition of methyl and terminal alkynes to chiral IV-f-butanesulfinyl ketimines (to form 3-amino oxindoles). Zinc-BINOL complexes have been used to achieve enantioselective addition of terminal alkynes to N-(diphenylphosphinoyl)imines (up to 96% cc) and terminal 1,3-diynes to IV-arylimines to trifluoropyruvates (up to 97% yield and 97% ee). ... [Pg.7]

A QUINAP auxiliary (21), bound to copper , gives excellent enantioselectivity in the addition of terminal alkynes to isolated isoquinoline iminium cations.55... [Pg.9]

Scheme 2.26 Enantioselective conjugate addition of terminal alkynes to a,p-unsaturated thioamides with the use of chiral Cu(i) complex, Li(OC6H4- 3-OMe), and chiral phosphoric acid. Scheme 2.26 Enantioselective conjugate addition of terminal alkynes to a,p-unsaturated thioamides with the use of chiral Cu(i) complex, Li(OC6H4- 3-OMe), and chiral phosphoric acid.
The Cu(I)-catalyzed direct addition of terminal alkynes to imines generated in situ from aldehydes and amines affords synthetically useful propargylamines. This metal-catalyzed carbon-carbon bond formation is best performed in toluene but water is also a convenient solvent. While the achiral process is mediated by the bimetallic catalytic system RuCls/CuBr, CuOTf in conjunction with chiral bis(oxazolines) has been found optimal for enantioselective additions (eq 119). [Pg.177]

C. Wei, C.-J. Li, J. Am. Chem. Soc. 2002, 124, 5638-5639. Enantioselective direct-addition of terminal alkynes to imines catalyzed by copper(I)pybox complex in water and in toluene. [Pg.123]

Benaglia and coworkers have developed a number of chiral ligands based on binaphthyl diamine (190) for CuOTf-catalyzed additions of terminal alkynes to preformed imines (Scheme 17.39) [51]. In a screen of the parent binaphthyl diamine (190) and N-alkylated derivatives, ligand (190) was found to provide moderate enantioselectivity in the addition of phenylacetylene (189) to imine (188). The selectivity could be improved by using bis-imine derivative (191) as the chiral ligand in the reaction [52]. [Pg.402]

Meanwhile, Carreira and coworkers introduced enantioselective addition of a terminal alkyne to an aldehyde in the presence of Zn(OTf)2, Et3N and IV-methylephedrine 41 (equation 22)88. The amounts of Zn(OTf)2 and Et3N were later reduced to a catalytic amount88b. This catalytic system has been employed by another group89 and the enantioselective alkynylation of a-ketoesters has been examined90. [Pg.566]

The asymmetric hydrogenation of enol esters is an alternative to asymmetric ketone hydrogenation. The precursors can be prepared from the ketones but also via ruthenium-catalyzed addition of the carboxylic acids to the 2-postion of terminal alkynes. This latter method allows the study of the effect of the carboxylate on the enantioselectivity of the asymmetric hydrogenation. A remarkable study by Reetz and colleagues established that it is possible to hydrogenate enolate... [Pg.275]

Hydroboration of terminal alkynes followed by the B/Zn exchange and enantioselective catalytic addition to aldehydes serves as a simple and efficient method for the preparation of chiral nonracemic allylic alcohols. [Pg.309]

In the context of a practical synthesis of the HIV reverse transcriptase inhibitor efavirenz (300), the enantioselective addition of metalated terminal acetylenes to ketones was studied and developed at Merck (Scheme 2.37) [184], The key enantioselective addition of the lithium acetylide prepared from 298 to ketone 296 in the presence of amino alcohol 297 proceeded with impressive enantioselectivity additionally, the process can be conducted on multi-kilogram scale. Careful mechanistic studies including spectroscopic work by Collum suggested that the alkyne addition proceeds via the cubic lithium tetramer 301 [185],... [Pg.55]


See other pages where Enantioselective addition of terminal alkynes is mentioned: [Pg.114]    [Pg.95]    [Pg.706]    [Pg.114]    [Pg.95]    [Pg.706]    [Pg.218]    [Pg.392]    [Pg.215]    [Pg.339]    [Pg.339]    [Pg.147]    [Pg.133]    [Pg.75]    [Pg.131]    [Pg.206]    [Pg.563]    [Pg.565]    [Pg.70]    [Pg.301]    [Pg.143]    [Pg.133]    [Pg.5237]    [Pg.226]    [Pg.402]    [Pg.226]    [Pg.257]    [Pg.286]    [Pg.178]    [Pg.29]    [Pg.30]    [Pg.178]    [Pg.574]   


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Addition alkynes

Addition of alkynes

Enantioselective additions

Enantioselective alkyne

Recent Developments in Enantioselective Addition of Terminal Alkynes to Aldehydes

Terminal alkynes

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