Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Chemoselective

Palladium catalyzed cycloisomerizations of 6-cn-l-ynes lead most readily to five-membered rings. Palladium binds exclusively to terminal C = C triple bonds in the presence of internal ones and induces cyclizations with high chemoselectivity. Synthetically useful bis-exocyclic 1,3-dienes have been obtained in high yields, which can, for example, be applied in Diels-Alder reactions (B.M. Trost, 1989). [Pg.84]

The oxidation of terminal alkenes with an EWG in alcohols or ethylene glycol affords acetals of aldehydes chemoselectively. Acrylonitrile is converted into l,3-dioxolan-2-ylacetonitrile (69) in ethylene glycol and to 3,3-dimetho.xy-propionitrile (70) in methanol[28j. 3,3-Dimethoxypropionitrile (70) is produced commercially in MeOH from acrylonitrile by use of methyl nitrite (71) as a unique leoxidant of Pd(0). Methyl nitrite (71) is regenerated by the oxidation of NO with oxygen in MeOH. Methyl nitrite is a gas, which can be separated easily from water formed in the oxidation[3]. [Pg.31]

With higher alkenes, three kinds of products, namely alkenyl acetates, allylic acetates and dioxygenated products are obtained[142]. The reaction of propylene gives two propenyl acetates (119 and 120) and allyl acetate (121) by the nucleophilic substitution and allylic oxidation. The chemoselective formation of allyl acetate takes place by the gas-phase reaction with the supported Pd(II) and Cu(II) catalyst. Allyl acetate (121) is produced commercially by this method[143]. Methallyl acetate (122) and 2-methylene-1,3-diacetoxypropane (123) are obtained in good yields by the gas-phase oxidation of isobutylene with the supported Pd catalyst[144]. [Pg.38]

The wM-diacetate 363 can be transformed into either enantiomer of the 4-substituted 2-cyclohexen-l-ol 364 via the enzymatic hydrolysis. By changing the relative reactivity of the allylic leaving groups (acetate and the more reactive carbonate), either enantiomer of 4-substituted cyclohexenyl acetate is accessible by choice. Then the enantioselective synthesis of (7 )- and (S)-5-substituted 1,3-cyclohexadienes 365 and 367 can be achieved. The Pd(II)-cat-alyzed acetoxylactonization of the diene acids affords the lactones 366 and 368 of different stereochemistry[310]. The tropane alkaloid skeletons 370 and 371 have been constructed based on this chemoselective Pd-catalyzed reactions of 6-benzyloxy-l,3-cycloheptadiene (369)[311]. [Pg.70]

Chemoselective C-alkylation of the highly acidic and enolic triacetic acid lactone 104 (pAl, = 4.94) and tetronic acid (pA, = 3.76) is possible by use of DBU[68]. No 0-alkylation takes place. The same compound 105 is obtained by the regioslective allylation of copper-protected methyl 3,5-dioxohexano-ate[69]. It is known that base-catalyzed alkylation of nitro compounds affords 0-alkylation products, and the smooth Pd-catalyzed C-allylation of nitroalkanes[38.39], nitroacetate[70], and phenylstilfonylnitromethane[71] is possible. Chemoselective C-allylation of nitroethane (106) or the nitroacetate 107 has been applied to the synthesis of the skeleton of the ergoline alkaloid 108[70]. [Pg.305]

Chemoselectivity in the cycloaddition of 2-methylenecycloheptenone (174) changes on addition of In(acac)3. The allylic carbonate 175 reacts with the ketone 174 in the presence of In(acac)3 to give the methylenetetrahydrofuran 176, and the methylenecyclopentane 177 is obtained in its absence[l 13], The cycloaddition of ynones to produce the methylenetetrahydrofuran proceeds smoothly only in the presence of In(acac)3 (10 mol%)[114]. [Pg.314]

Hydroxylysine (328) was synthesized by chemoselective reaction of (Z)-4-acet-oxy-2-butenyl methyl carbonate (325) with two different nucleophiles first with At,(9-Boc-protected hydroxylamine (326) under neutral conditions and then with methyl (diphenylmethyleneamino)acetate (327) in the presence of BSA[202]. The primary allylic amine 331 is prepared by the highly selective monoallylation of 4,4 -dimethoxybenzhydrylamine (329). Deprotection of the allylated secondary amine 330 with 80% formic acid affords the primary ally-lamine 331. The reaction was applied to the total synthesis of gabaculine 332(203]. [Pg.334]

Stereoselective and chemoselective semihydrogenation of the internal alkyne 208 to the ew-alkene 210 is achieved by the Pd-catalyzed reaction of some hydride sources. Tetramethyldihydrosiloxane (TMDHS) (209) i.s used in the presence of AcOH[116]. (EtO)3SiH in aqueous THF is also effective for the reduction of alkynes to di-alkenes[l 17], Semihydrogenation to the d.v-alkene 211 is possible also with triethylammonium formate with Pd on carbon[118]. Good yields and high cis selectivity are obtained by catalysis with Pd2fdba)3-Bu3P[119],... [Pg.497]

The chemoselective desilylation of one of the two different silyi enoi ethers in 10 to give the monosilyl enol ether II is realized by the Pd-catalyzed reaction of Bu3SnF. The chemoselectivity is controlled by steric congestion and the relative amount of the reagent[7,8]. An interesting transformation of the 6-alkoxy-2,3-dihydro-6//-pyran-3-one 12 into the cyclopentenone derivative 13 proceeds smoothly with catalysis by Pd(OAc)2 (10 mol%)[9]. [Pg.530]

The a, /3-epoxy ketone 119 and esters are hydrogenolyzed with triethylam-monium formate or H2 chemoselectively to aldols[116]. [Pg.542]

Sodium cyanoborohydride is remarkably chemoselective. Reduction of aldehydes and ketones are, unlike those with NaBH pH-dependent, and practical reduction rates are achieved at pH 3 to 4. At pH 5—7, imines (>C=N—) are reduced more rapidly than carbonyls. This reactivity permits reductive amination of aldehydes and ketones under very mild conditions (42). [Pg.304]

Sodium cyanoborohydride has become important in biochemical appHcations that require hydrolytic stabiHty of the reducing agent and chemoselectivity, in sensitive molecules. It is also a preferred reagent for oxime reductions. [Pg.304]

Many other examples ia the Hterature illustrate the possibiUties of chemoselective hydroborations (124,186—189). For example, selectivity between double and triple bonds has been shown (124). [Pg.312]

Addition to Carbonyl Compounds. Unlike Grignard and alkykitliium compounds, trialkylboranes are inert to carbonyl compounds. The air-catalyzed addition to formaldehyde is exceptional (373). Alkylborates are more reactive and can transfer alkyl groups to acyl halides. The reaction provides a highly chemoselective method for the synthesis of ketones (374). [Pg.319]

A catalyst, usually acid, is required to promote chemoselective and regioselective reduction under mild conditions. A variety of organosilanes can be used, but triethylsilane ia the presence of trifiuoroacetic acid is the most frequendy reported. Use of this reagent enables reduction of alkenes to alkanes. Branched alkenes are reduced more readily than unbranched ones. Selective hydrogenation of branched dienes is also possible. [Pg.28]

AC2O, BF3 Et20, THE, 0°. These conditions give good chemoselectivity for the most nucleophilic hydroxyl group. Alcohols are acetylated in the presence of phenols. [Pg.89]

The imidazolidine was prepared from an aldehyde with A/,N -dimethyl-1,2-eth-ylenediamine (benzene, heat, 78% yield) and cleaved with Mel (Et20 HjO, 92% yield). Derivatization is chemoselective for aldehydes. The imidazolidine is stable to BuLi and LDA. The diphenylimidazolidine has been prepared analogously and can be cleaved with aqueous HCl. ... [Pg.218]

Epoxides are regio- and stereoselectively transformed into fluorohydrins by silicon tetrafluoride m the presence of a Lewis base, such as diisopropyleth-ylamme and, m certain instances, water or tetrabutylammonium fluoride The reactions proceed under very mild conditions (0 to 20 C in 1,2-diohloroethane or diethyl ether) and are highly chemoselective alkenes, ethers, long-chain internal oxiranes, and carbon-silicon bonds remain intact The stereochemical outcome of the epoxide ring opening with silicon tetrafluoride depends on an additive used, without addition of water or a quaternary ammonium fluoride, as fluorohydrins are formed, whereas m the presence of these additives, only anti opening leading to trans isomers is observed [17, 18] (Table 2)... [Pg.204]

Huonnations with DAST proceed with high chemoselectivity In general, under very mild reaction conditions usually required for the replacement of hydroxyl groups, other functional groups, including phenolic hydroxyl groups [112], remain intact This provides a method for selective conversion of hydroxy esters [95 97] (Table 6), hydroxy ketones [120, 121], hydroxy lactones [722, 123], hydroxy lactams [124] and hydroxy nitriles [725] into fluoro esters, fluoro ketones, fluoro lactones, fluoro lactams, and fluoro nitnles, respectively (equations 60-63)... [Pg.228]

DIBAL, NiCl2(dppp), toluene, CH2CI2, THF, or ether, 80-97% yield. These conditions are chemoselective for simple alkyl and phenolic allyl ethers. More highly substituted allyl ethers are unreactive. [Pg.72]

Allyl bromide, Sb(OEt)3, 80°, 2-6 h, 85-98% yield. This method is chemoselective for aldehydes in the presence of ketones. [Pg.298]

Nal, CeCl3 7H20, CH3CN, rt, 0.5-21 h, 84-96% yield. Chemoselective cleavage of ketone derivatives is observed in the presence of aldehyde derivatives, and enone ketals are cleaved in the presence of simple ketone ketals. [Pg.319]

HSCH2CH2SH, FeCb-Si02, CH2CI2, < 1 min-7 h."" Montmorillonite Clay can also be used as a support medium for the ferric ion (75-98% yield ). In this case, the reaction is chemoselective for aldehydes."" ... [Pg.335]

NaSMe, MeOH, 23°, 81-95% yield. This procedure is chemoselective for removal of a thioacetate in the presence of an acetate. [Pg.483]

In transforming bis-ketone 45 to keto-epoxide 46, the elevated stereoselectivity was believed to be a consequence of tbe molecular shape — tbe sulfur ylide attacked preferentially from tbe convex face of the strongly puckered molecule of 45. Moreover, the pronounced chemoselectivity was attributed to tbe increased electropbilicity of the furanone versus the pyranone carbonyl, as a result of an inductive effect generated by tbe pair of spiroacetal oxygen substituents at tbe furanone a-position. ... [Pg.6]


See other pages where Chemoselective is mentioned: [Pg.66]    [Pg.147]    [Pg.172]    [Pg.198]    [Pg.224]    [Pg.320]    [Pg.353]    [Pg.363]    [Pg.367]    [Pg.387]    [Pg.388]    [Pg.393]    [Pg.531]    [Pg.305]    [Pg.28]    [Pg.173]    [Pg.176]    [Pg.98]    [Pg.211]    [Pg.46]    [Pg.303]   
See also in sourсe #XX -- [ Pg.210 ]

See also in sourсe #XX -- [ Pg.318 ]

See also in sourсe #XX -- [ Pg.315 ]

See also in sourсe #XX -- [ Pg.16 , Pg.19 , Pg.19 , Pg.299 , Pg.307 , Pg.329 ]




SEARCH



2- Hexenal chemoselectivity

Acetylation chemoselective

Acylating reagents chemoselective

Acylation chemoselectivity

Addition chemoselectivity

Aim for Higher Chemoselectivity to Avoid Protecting Groups

Alcohol chemoselective oxidation

Alcohols chemoselective agents

Alcohols chemoselectivity

Aldehyde chemoselective reduction

Aldehydes chemoselectivity

Aldehydes, catalytic chemoselective reducing

Aldol chemoselective

Alkenes chemoselective

Alkenes, internal, chemoselective

Alkenes, internal, chemoselective hydroformylation

Alkylation chemoselectivity

Allylic chemoselectivity

Amines chemoselective reduction

Amines chemoselectivity

Amino sugars chemoselectivity

Ammonia chemoselectivity

Arene chemoselectivity

Armed-disarmed concept chemoselectivity

Aromatic chemoselective hydrogenation

Aromatic compounds chemoselective acylation

Aryl halides chemoselectivity

Baeyer-Villiger reaction chemoselectivity

Birch reduction chemoselectivity

Borane, chemoselectivity

Boron compounds chemoselectivity

Boronic chemoselective transformations

Bromination chemoselective

Butanal, 2-ethylreaction with organometallic compounds chemoselectivity

C chemoselectivity

Carbinols chemoselectivity

Carbocyclizations chemoselectivity

Catalysis Chemoselectivity

Chemoselective Agents for Oxidizing Alcohols

Chemoselective Carbonylation Reactions of Enol Triflates and lodoalkenes

Chemoselective Cleavage

Chemoselective Deprotonations

Chemoselective Diels-Alder Reactions

Chemoselective Functionalization of Different Carbonyl Group

Chemoselective Ligation

Chemoselective Michael and Aldol Reactions

Chemoselective SN reaction

Chemoselective acetal

Chemoselective activation

Chemoselective acylation

Chemoselective alcohol-protecting group

Chemoselective aldehyde

Chemoselective aldimine

Chemoselective alkylation

Chemoselective allylic alcohols

Chemoselective allylic oxidation

Chemoselective carbonyl group

Chemoselective carbonyl group reduction

Chemoselective condensation sequence

Chemoselective conjugation

Chemoselective control

Chemoselective control elements

Chemoselective coupling

Chemoselective coupling reaction

Chemoselective cyclopropanation

Chemoselective ester

Chemoselective functionalization

Chemoselective functionalization ketone

Chemoselective glycosylation

Chemoselective glycosylation (armed-disarmed

Chemoselective glycosylations

Chemoselective hydrogenation

Chemoselective hydrogenation catalyst

Chemoselective hydroxylation

Chemoselective hydroxylation of bicyclic triene

Chemoselective ligation strategy

Chemoselective method

Chemoselective nitro group

Chemoselective nitrone formation

Chemoselective oxidation

Chemoselective oxidation, of alcohol

Chemoselective polymerization

Chemoselective protection

Chemoselective protection Subject

Chemoselective protection amino alcohols

Chemoselective reactions

Chemoselective reactions epoxidation

Chemoselective reactions hydroboration

Chemoselective reactions hydrogenation

Chemoselective reactions oxidation

Chemoselective reactions reduction

Chemoselective reactions sulfide

Chemoselective reactivity

Chemoselective reducing agents

Chemoselective reducing agents aldehydes

Chemoselective reducing agents ketones

Chemoselective reduction of aldehyd

Chemoselective reduction of keton

Chemoselective reduction of nitroaromatics

Chemoselective sensors

Chemoselective strategies

Chemoselective strategies armed-disarmed approach

Chemoselective strategies strategy

Chemoselective substitution

Chemoselective tandem acylation of the

Chemoselective tandem acylation of the Blaise

Chemoselective technology

Chemoselective transformation

Chemoselective unsaturated aldehydes

Chemoselective unsaturated esters

Chemoselective unsaturated ketones

Chemoselective vinyl epoxides

Chemoselective, Solvent-free aldol Condensation Reactions

Chemoselectivity

Chemoselectivity

Chemoselectivity 1,3-dipolar cycloadditions

Chemoselectivity E2 eliminations

Chemoselectivity Haloform reaction

Chemoselectivity Wittig olefination

Chemoselectivity activation

Chemoselectivity amine reduction

Chemoselectivity and Functional Group Compatibility

Chemoselectivity and Reactivity

Chemoselectivity and protecting groups

Chemoselectivity carbonyl

Chemoselectivity carbonyl compounds

Chemoselectivity carbonylation

Chemoselectivity carboxylic acid reductions

Chemoselectivity compounds

Chemoselectivity concentrations, effect

Chemoselectivity conformational control

Chemoselectivity crossed aldol condensations

Chemoselectivity cyclization

Chemoselectivity cyclopropanation

Chemoselectivity definition

Chemoselectivity donor/acceptor coupling

Chemoselectivity donors

Chemoselectivity elimination

Chemoselectivity epoxide reduction

Chemoselectivity examples illustrating

Chemoselectivity functionalization

Chemoselectivity glycosides

Chemoselectivity glycosylation using glycosyl

Chemoselectivity hydride donor addition

Chemoselectivity hydrogenation

Chemoselectivity hydrolase

Chemoselectivity hydrometallation

Chemoselectivity intramolecular cycloadditions

Chemoselectivity ketone hydrogenation

Chemoselectivity kinetic control

Chemoselectivity nitrogen substituent

Chemoselectivity nucleophilic substitutions

Chemoselectivity of Radical Brominations

Chemoselectivity of carbenoid transformations Rh2

Chemoselectivity optically active compounds

Chemoselectivity organometallic compound

Chemoselectivity other donors

Chemoselectivity oxidation

Chemoselectivity phosphates

Chemoselectivity reactions

Chemoselectivity regioselectivity

Chemoselectivity rhodium

Chemoselectivity selective reactions and protection

Chemoselectivity selectivity

Chemoselectivity sensitizers effect

Chemoselectivity solvents effect

Chemoselectivity thermodynamic control

Chemoselectivity versus Classical Resolution Comparison

Chemoselectivity, bromination

Chemoselectivity, bromination alkenes

Chemoselectivity, control

Chemoselectivity, dioxirane epoxidation

Chemoselectivity, domino reactions

Chemoselectivity, in metal-catalysed

Chemoselectivity, nitrile oxide cycloadditions

Coating chemoselective polymer

Conjugate reduction chemoselective

Control of Chemoselectivity

Controlled Reversal of Chemoselectivity Using Titanium Ate Complexes

Copolymerization chemoselectivity

Copper chemoselectivity

Cross-coupling chemoselective

Cumulative Subject chemoselectivity

Cyclization chemoselective

Cycloaddition chemoselectivity

Cycloadditions chemoselectivity

Cyclobutanones chemoselective epoxidation

Dehalogenation chemoselective

Dendrimers chemoselectivity

Dianions, chemoselective reactions

Diels chemoselective

Dissolving metals chemoselectivity

Diverse chemoselectivity

Donors, armed/disarmed chemoselectivity

Effect of Dienophile Substituents on Chemoselectivity

Effect of Electron-Rich Dienophiles on Chemoselectivity

Effect of Sensitizers and Solvents on Chemoselectivity

Electrophilic addition chemoselectivity

Enol chemoselective carbonylation reactions

Enol silyl ethers chemoselectivity

Enolization chemoselectivity

Enones chemoselectivity

Enzyme chemoselectivity

Epoxidation chemoselective

Epoxides Chemoselective synthesis

Epoxides chemoselectivity of formation

Ester hydrolysis chemoselectivity

Esters chemoselective reductions

Exploiting Enzyme Chemoselectivity and Regioselectivity

External reagents, 1,3-dipolar cycloaddition chemoselectivity

Glycosyl activation, chemoselective

Glycosylation, chemical chemoselective

Hydrides imines, chemoselectivity

Hydroalumination chemoselectivity

Hydroboration chemoselective

Hydrogen bonding effects chemoselectivity

Hydrogenation chemoselectively

Hydrozirconation chemoselectivity

Immobilization, chemoselective

Intramolecular Wittig reaction, chemoselective

Intramolecular chemoselectivity

Iodine chemoselective activation

Iridium chemoselectivity

Ketenes chemoselectivity

Ketone copper, chemoselectivity

Ketones chemoselective

Ketones chemoselective reduction

Ketones chemoselective/stereoselective

Ketones chemoselectivity

Ketones, catalytic chemoselective reducing

Lanthanide chemoselectivity

Lithium aluminium hydride: chemoselective

Lithium aluminium hydride: chemoselective reduction with

Lithium aluminium hydride: chemoselective reductions

Lithium enolates chemoselectivity

Manganese Organometallics for the Chemoselective Synthesis of Polyfunctional Compounds

Metal-dependent chemoselectivity

Methyl chemoselective deprotection

Methylation chemoselective

Methylenation chemoselective

Mitsunobu reaction chemoselectivity

Modification of chemoselectivity and

Modification of chemoselectivity and regioselectivity

Nitrile chemoselectivity

Nucleophilic displacement chemoselectivity

Nucleophilic substitution chemoselectivities

Olefin chemoselective

Oligosaccharides chemoselective glycosylations

Organomanganese reagents chemoselectivity

Peptides chemoselective bond

Peptides chemoselective ligation

Peroxycarbonic acid, o-trichloroethylcyclobutanones chemoselective epoxidation

Phenols chemoselective protection

Phenylation chemoselective

Phosphorylation, chemoselective

Pinacol rearrangement Chemoselectivity

Polycondensation, chemoselective

Polycyclic aromatic hydrocarbons chemoselectivity

Primary alcohols, chemoselectivity

Primary alcohols, chemoselectivity oxidation

Product chemoselectivity

Propargylic chemoselectivity aldehydes

Propargylic chemoselectivity ketones

Protecting chemoselective amine group

Purification of large peptides using chemoselective tags

Radical bromination chemoselectivity

Radical brominations chemoselectivity

Radical cations chemoselectivity

Reactions with organometallic compounds chemoselectivity

Reducing agent, hindered chemoselectivity

Reduction chemoselectivity

Reduction, chemoselective

Reformatsky reaction chemoselectivity

Regio- and Chemoselective Reductions

Regiospecificity and Chemoselectivity of the

Retrosynthetic analysis chemoselectivity problems

Ruthenium chemoselectivity

Sodium cyanoborohydride imines, chemoselectivity

Stereochemistry chemoselective

Strategy 11 Chemoselectivity

Strategy II Chemoselectivity

Sulfides chemoselective epoxidation

Sulfides, allylic chemoselective oxidation

Sulfones chemoselective

Synthesis chemoselective

Synthesis chemoselectivity

Synthesis of Peptides by Chemoselective Ligation

Temporary chemoselectivity

Thioglycosides chemoselective glycosylations

Titanium, dichlorodimethylreaction with carbonyl compounds chemoselectivity

Titanium, dichlorodiphenylreaction with carbonyl compounds chemoselectivity

Titanium, trichloromethylproperties chemoselectivity

Titanium, tris methylproperties chemoselectivity

Unsaturated esters, hydrogenation chemoselective

Unsaturated ketones, hydrogenation chemoselective

Unusual Chemoselectivity

Use of Protecting Groups for Chemoselective Glycosylations

Vinyl chemoselective carbonylation

Wolff-Kishner reduction chemoselectivity

Zirconium, alkyltributoxyreaction with carbonyl compounds chemoselectivity

Zirconium, aryltributoxyreaction with carbonyl compounds chemoselectivity

© 2024 chempedia.info