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MBH carbonates

Racemic MBH carbonates can be converted into densely functionalized compounds 267 featuring two adjacent stereocenters, one of them bearing four carbon substituents, by reaction with cyano esters in the presence of a catalytic amount of a modified cinchona alkaloid (3-ICPD in high enantioselectivities and fair diastereoselectivities (Scheme 3.106). ... [Pg.257]

Chen et al. have found that commercially available modified cinchona alkaloids [(DHQD)2AQN] are outstanding catalysts for the asymmetric allylic alkylation (AAA) reaction of MBH carbonates with a,a-dicyanoolefins 268 or 3-substituted oxindoles 269. Enantioenriched compounds 270 and 271, respectively, with multifunctional frameworks bearing adjacent stereogenic centers were obtained in excellent stereoselectivities (Scheme 3.107). [Pg.258]

Chen et al. developed the first asymmetric and chemoselective A-allylic alkylation of indoles with MBH carbonates. This method was realized by employing modified cinchona alkaloids (DHQD)2PHAL as organocatalysts. Either electron-rich or electron-deficient indoles could be employed and moderate to excellent enantioselectivity was achieved (62-93% ee) (Scheme 3.115). ... [Pg.262]

The reactions of f-butyl peroxylate anion with ethyl 2-methylene-3-acetoxy-butanoate and with ethyl 2-bromomethylbut-2-enoate have been studied by Mailard and co-workers, respectively (Scheme 3.134). " They found that both reactions resulted in the y-attack products 311 in low yields. However, the allyl f-butyl peroxides 312 were obtained in 45% yield when the reaction was carried out in the presence of poly(ethylene oxide) 400. Subsequently, 312 was converted into the corresponding glycidic ester 313 by heating in benzene. Recently, Chen et al. developed the first peroxo-asymmetric allylic alkylation of bulky hydroperoxyalkanes with MBH carbonates with catalysis by commercially available modified cinchona alkaloids. Peroxides 314 were generally... [Pg.270]

The allyhe-allylic alkylation products 409 of a,a-dicyanoalkenes and MBH carbonates derived from methyl vinyl ketone (MVK) can undergo cyclization... [Pg.289]

With the development of the enantioselective allylic-allylic alkylation of a,a-dicyanoalkenes and MBH carbonates by dual organocatalysis of commercially available modified cinchona alkaloids and (5)-BINOL, Chen and co-workers have delivered an elegant construction of cyclohexene derivatives. The intramolecular Michael reaction of allylic allylic alkylation product 75a could be cyclized to give the desired cyclohexene 76 in the presence of DBU (Scheme 4.25). In the presence of nucleophile BnNH2, allylic compound 75b furnished an imexpected cyclic product 77 rather than the formal double Michael adduct. Interestingly, the reaction of a,a-dicyanoalkene 79 and MBH carbonate 80 under optimized catalytic conditions directly afforded cyclohexene derivatives 81a-c in... [Pg.335]

With the development of asymmetrie allylic N-alkylation from MBH carbonates, a method for constructing novel tricycle compounds with indole ring was disclosed by Chen (Scheme 4.156). A regioselective bromination was... [Pg.406]

Two years later, Du et al. [ 116] documented that the reaction of MBH carbonates and TsNH2 or phthalamide can be catalyzed by p-isocupreidine to give the desired amination derivatives with good yields and again with moderate enatioselectivies (< 70% ee). The absolute configuration of the major enantiomer was not determined (Scheme 11.36). [Pg.412]

The enantioselective allylic substitution of MBH carbonates with allylamines was successfully applied by Wang and co-workers [119] recently. The corresponding... [Pg.412]

Recently, using the modified cinchona alkaloid (DHQD>2AQN 53 as catalyst, the allylic alkylation of benzophenone imines [120] and 7V-acetyl enamides [121] with MBH carbonates has been achieved (Scheme 11.40). [Pg.414]

SCHEME 11.37, Asymmetric allylic amination reaction of imides with MBH carbonates. [Pg.415]

SCHEME 11.38. Chemoselective asymmetric allylic amination of indoles with MBH carbonates. [Pg.416]

SCHEME 11.39. Asymmetric allylic substitution of MBH carbonates with allylamines. [Pg.416]

SCHEME 11.40. Enantioselective allylic amination of MBH carbonates with henzophenone imine and Al-acetyl enamides. [Pg.416]

In addition to the organophosphine catalyst 54, several useful chiral phosphines have been developed by other groups. The Hou group constructed a planar [2.2] paracyclophane phosphine 55 that catalyzed the allylic substitution of a series of MBH carbonates and acetates with phthalimide to afford products with variable results (Scheme 11.42) [123]. Screening of the solvents revealed that THF and DME are the best one in terms of both reactivity and enantioselectivity. [Pg.417]

A Lewis base-assisted Brpnsted base catalysis strategy has been used for direct asymmetric vinylogous alkylation of allylic sulfones with Morita-Baylis-Hillman (MBH) carbonates, in which a strong Brpnsted base, f-butoxy anion, generated in situ from a tertiary amine catalyst and MBH carbonate, is crucial in activating unstabilized nucleophiles. The y-regio-selective alkylation products were obtained with good to excellent enantiomeric excess (up to 98% ee) values when catalysed by a modified cinchona alkaloid. [Pg.343]

The annulation between Morita-Baylis-Hillman (MBH) carbonates and enones takes place under PBU3 catalysis (Scheme 6.7). Cascade [3-f2] cyclization-allylic... [Pg.160]

The multifunctional thiourea-phosphine-catalyzed asymmetric [3-1-2] annulation of MBH carbonates with maleimides affords functionalized fused cyclopentenes bearing three contiguous stereogenic centers with high enantiomeric excess (Scheme 6.29) [33]. [Pg.171]

A related approach for the synthesis of spirocyclopenteneoxindoles was developed by Barbas and coworkers. Chiral diphosphines catalyzed the [3+2] cycloaddition between the A-protected methyleneindolin-2-ones 17b and the Morita-Baylis-Hillman (MBH) carbonates 37 [18]. This reaction was initiated by the displacement of the carbonate moiety by the phosphine VI, an addition-elimination mechanism, which was followed by the deprotonation to afford ylide 39. A regioselective nucleophilic addition on 17 by 39, followed by an intramolecular conjugate addition, afforded intermediate 40 that, after elimination of PR3, delivered the corresponding spirocycle 41 (Scheme 10.11). [Pg.284]

Under the optimized conditions, the spirocyclic compounds 41 were obtained in high yields and excellent enantioselectivities. The only limitation of the reaction was the use of aliphatic MBH carbonates in this case, the enantioselectivity of the reaction decreased dramatically (Scheme 10.12). [Pg.285]

In 2011, Shi and coworkers reported a complementary [3+2] cycloaddition of MBH carbonates 42 with isatylidene malononitriles 43 [19]. They reported a simple example of the enantioselective version of this reaction that used a chiral phosphine bearing a thiourea moiety VII as the catalyst and afforded the product 44 in good yield and stereoselectivity (Scheme 10.13). [Pg.285]

Scheme 20.26 Generation of ylides from MBH carbonates under neutral conditions. Scheme 20.26 Generation of ylides from MBH carbonates under neutral conditions.
Recently, Barbas [47] and Lu [48] independently reported phosphinecycloaddition reactions between the isatin-derived alkenes 33 and MBH carbonates 34 for the synthesis of 3-spirocydopentene-2-oxindoles 36, the spiro scaffold of which is found as a key structure in many natural products and drug candidates (Scheme 20.28). [Pg.568]

This strategy was used to synthesize spirocyclopenteneoxindoles, as well as stereodefined cyclopentenes. Likewise, Hu reported a [3 -f 2] annulation reaction of 2-atylideneindane-l,3-diones with MBH carbonates that proceeded smoothly in the presence of a multifunctional thiourea-phosphine catalysts to produce the corresponding quaternary carbon centered spirocyclic cyclopentenes. A phosphine-triggered tandem [3 + 4] annulation reaction between MBH carbonates and 1,4-diheteroatom dinucleophiles was described, which provided access to saturated seven-membered 1,4-heterocycles. Analogously, MBH carbonates were used as C3 synthons in asymmetric [3 + 2] annulation reactions for the asymmetric synthesis of 3-spirocyclopentene-2-oxindoles. Another kind of annulation reaction for the construction of highly functionalized stereodefined cyclopentene skeletons involved a Rauhut-Currier Domino Reaction. Finally, an efficient asymmetric [3 + 2] cycloaddition reaction between MBH carbonates of isatins and... [Pg.104]


See other pages where MBH carbonates is mentioned: [Pg.363]    [Pg.412]    [Pg.414]    [Pg.161]    [Pg.171]    [Pg.16]    [Pg.570]    [Pg.570]    [Pg.16]   
See also in sourсe #XX -- [ Pg.124 ]




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