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Reactions with nitroolefins

Chiral imidazolidinones like 20 serve as chiral organocatalysts for the enantioselective reactions of 2-siloxyfuran with a y9-unsaturated aldehydes through oc,fi-unsaturated iminium species (Scheme 3-83)J The Mukaiyama-Michael reaction with nitroolefines provides an access to 1,3-dicarbonyl compounds... [Pg.437]

The alkylation of enamines with nitroolefins, which gives intermediates for reductive cyclization (6S2), also provided an example of a stable cycliza-tion product derived from attack of the intermediate imonium function by the nitro anion (683). A previously claimed tetrasubstituted enamine, which was obtained from addition of a vinylsulfone to morpholinocyclohexene (314), was shown to be the corresponding cyclobutane (684). Perfluoro-olefins also gave alkylation products with enamines (685). Reactions of enamines with diazodicarboxylate (683,686) have been used diagnostically for 6-substituted cyclohexenamines. In a reaction of 2-penten-4-one with a substituted vinylogous amide, stereochemical direction was seen to depend on solvent polarity (687). [Pg.375]

The regiochemical control of Pd-catalyzed hydride transfer reaction is much more effective than that of the radical denitration, as shown in Eq. 7.98. The base-catalyzed reaction of nitroolefins with aldehydes followed by denitration provides a new synthetic method of homoallyl alcohols (Eq. 7.99).140 Exomethylene compounds are obtained by denitration of cyclic allylic nitro compounds with Pd(0), HC02H and Et3N (Eq. 7.100).140b... [Pg.213]

Hydrazones are also useful substrates in the preparation of pyrazoles. Reaction of N-monosubstituted hydrazones with nitroolefins led to a regioselective synthesis of substituted pyrazoles <060L3505>. lf/-3-Ferrocenyl-l-phenylpyrazole-4-carboxaldehyde was achieved by condensation of acetylferrocene with phenylhydrazine followed by intramolecular cyclization of the hydrazone obtained under Vilsmeier-Haack conditions <06SL2581>. A one-pot synthesis of oxime derivatives of l-phenyl-3-arylpyrazole-4-carboxaldehydes has been accomplished by the Vilsmeier-Haack reaction of acetophenone phenylhydrazones <06SC3479>. [Pg.210]

Interestingly, bis(methylthio)-l-nitroethylene (380) reacts with dimetallic zinc-copper species leading to the corresponding exo-methylene cycloalkenes, such as 381 (Scheme 100) . / -Disubstitutcd nitroolefins are especially difficult to prepare by nitroaldol condensation. The addition of zinc-copper reagents to nitroolefins followed by a reaction with phenylselenyl bromide produces, after IFO, oxidation, EtZ mixtures of -disubstituted nitroalkenes, such as 382 (Scheme 100) . [Pg.356]

This topological rule readily explained the reaction product 211 (>90% stereoselectivity) of open-chain nitroolefins 209 with open-chain enamines 210. Seebach and Golinski have further pointed out that several condensation reactions can also be rationalized by using this approach (a) cyclopropane formation from olefin and carbene, (b) Wittig reaction with aldehydes yielding cis olefins, (c) trans-dialkyl oxirane from alkylidene triphenylarsane and aldehydes, (d) ketenes and cyclopentadiene 2+2-addition, le) (E)-silyl-nitronate and aldehydes, (f) syn and anti-Li and B-enolates of ketones, esters, amides and aldehydes, (g) Z-allylboranes and aldehydes, (h) E-alkyl-borane or E-allylchromium derivatives and aldehydes, (i) enamine from cyclohexanone and cinnamic aldehyde, (j) E-enamines and E-nitroolefins and finally, (k) enamines from cycloalkanones and styryl sulfone. [Pg.323]

Nitroolefins are attractive alternative acceptors to enones. In 1999, Barnes and Ji reported an efficient catalyst system for reaction of nitroolefins with 1,3-dicarbonyl compounds with high enantioselectivity (up to 97% ee Scheme 19) [22], Using this method, a highly functionalized nitro compound 38, an important intermediate in the synthesis of an endothelin-A antagonist, was prepared on a large scale in 88 % ee. In this case, the formation of a chiral Mg enolate as a reactive intermediate was proposed. [Pg.357]

Scheme 19. Catalytic reaction of nitroolefins with 1,3-dicarbonyl compounds. Scheme 19. Catalytic reaction of nitroolefins with 1,3-dicarbonyl compounds.
Whereas cyclic secondary enaminones and nitroolefins mainly yield indoles in which the enamine nitrogen is incorporated into the heterocyclus (equation 242), linear tertiary a-ketoenamines are shown to react with nitroolefines at low temperature under kinetic control to give 1,2-oxazine N-oxides as [4 + 2]-cycloadducts, followed by retro-Diels-Alder reaction or rearrangement under thermodynamic control which leads diastereo-selectively to aminocyclopentenes. The reaction is called [3 + 2]-carbocyclization, apparently because the ketoenamine is reacting as a 1,3-dipole. The products are hydrolysable to polysubstituted nitrocyclopentanones with retained configuration325 (equation 243). [Pg.619]

A similar reaction of nitroolefins with kctcnc silyl acetals provides y-keto esters but in this case only TiCE is an effective catalyst. Yields arc low unless titanium(IV) iso-propoxidc is added to suppress hydrolysis of the ketene silyl acetals. [Pg.500]

Serrano, J A, Moreno, M C, Rom, E, Arjona, O, Plumet, J, Jimenez, J, Enantioselective s3mthesis of cyclohexene nitro aldehydes via Diels-Alder reactions with sugar nitroolefins, J. Chem. Soc. Perkin. Trans 1, 3207-3212, 1991. [Pg.498]

Sharpless bis-cinchona alkaloids such as [DHQD]2PYR (163a) have proved to serve as highly efficient catalysts for the asymmetric vinylogous Michael addition of the electron-deficient vinyl malonitriles 164 as the nucleophilic species to nitroole-fins 124 [50], This process exhibited exclusive y-regioselectivity and high diastereo-and enantioselectivity. Only the anti-products 165 were observed in all reactions (Scheme 9.57). Of note, 1-tetralone did not react with nitroolefins under these... [Pg.282]

Scheme 5.19 Michael addition reactions of carbonyl compounds with nitroolefins. Scheme 5.19 Michael addition reactions of carbonyl compounds with nitroolefins.
The combination of titanium-TADDOL 34 mediates the reaction of diethylzinc with nitroolefins to afford the products in relatively high ees (Scheme 18) [77]. [Pg.1054]

Table 9.13 Thiourea catalysed Michael reaction of nitroolefins with indole... Table 9.13 Thiourea catalysed Michael reaction of nitroolefins with indole...
Seebach studied the conjugate addition reaction of nitroolefin 10 with butyllith-ium in the presence of the multidentate ligand 11 (accessible from tartaric acid), which yielded the adduct 12 in up to 58% ee (Scheme 4) [18]. [Pg.40]


See other pages where Reactions with nitroolefins is mentioned: [Pg.114]    [Pg.114]    [Pg.114]    [Pg.463]    [Pg.471]    [Pg.114]    [Pg.114]    [Pg.114]    [Pg.463]    [Pg.471]    [Pg.364]    [Pg.356]    [Pg.440]    [Pg.442]    [Pg.35]    [Pg.87]    [Pg.197]    [Pg.618]    [Pg.440]    [Pg.577]    [Pg.39]    [Pg.478]    [Pg.512]    [Pg.165]    [Pg.249]    [Pg.315]    [Pg.248]    [Pg.123]    [Pg.457]    [Pg.471]    [Pg.393]    [Pg.32]    [Pg.110]   
See also in sourсe #XX -- [ Pg.1037 ]

See also in sourсe #XX -- [ Pg.1037 ]




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Nitroolefination

Nitroolefins

Nitroolefins, reaction with dienes

With Nitroolefins

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