- Ti/Ni-based multimetallic system for the efficient allylation of carbonyl compounds
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A mild method for the allylation of carbonyl compounds is presented. This methodology allows the allylation of a broad range of carbonyl compounds starting with allyl carbonates as pronucleophiles. Noteworthy is that ketones, infrequent substrates in other related protocols, are suitable substrates under these reaction conditions. Moreover, the reaction proceeds at room temperature with the use of catalytic amounts of both Ni and Ti catalysts. The success of this strategy is based on the perfect match between the late transition metal (nickel) and the radical reagent (titanium). The use of Ni instead of Pd widens the scope of this transformation and makes this method more economical.
- Martinez-Peragon, Angela,Millan, Alba,Campana, Araceli G.,Rodriguez-Marquez, Irene,Resa, Sandra,Miguel, Delia,Alvarez De Cienfuegos, Luis,Cuerva, Juan M.
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supporting information; experimental part
p. 1499 - 1503
(2012/04/23)
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- Mesoporous aluminosilicate-catalyzed allylation of carbonyl compounds and acetals
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A mesoporous aluminosilicate (Al-MCM-41) was found to be an effective heterogeneous catalyst for the reaction of both carbonyl compounds and acetals with allylsilanes to afford the corresponding homoallyl silyl ethers and homoallyl alkyl ethers, respectively. Both the mesoporous structure and the presence of aluminum moiety were indispensable for the high catalytic activity of Al-MCM-41. Moreover, Al-MCM-41 could catalyze the reaction of acetals chemoselectively in the presence of the corresponding carbonyl compounds. The solid acid catalyst Al-MCM-41 could be recovered easily by filtration and could be reused three times without a significant loss of catalytic activity.
- Ito, Suguru,Hayashi, Akira,Komai, Hirotomo,Yamaguchi, Hitoshi,Kubota, Yoshihiro,Asami, Masatoshi
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experimental part
p. 2081 - 2089
(2011/04/19)
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- Allylation and crotylation of ketones and aldehydes using potassium organotrifluoroborate salts under lewis acid and montmorillonite k10 catalyzed conditions
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Two convenient highly diastereoselective protocols for the allylation and crotylation of ketones using practical, air- and water-stable potassium allyl and crotyltrifluoroborate salts have been developed. BF3-OEt 2 and montmorillonit
- Nowrouzi, Farhad,Thadani, Avinash N.,Batey, Robert A.
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supporting information; experimental part
p. 2631 - 2634
(2009/10/02)
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- Ti-catalyzed Barbier-type allylations and related reactions
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Titanocene(III) complexes, easily generated in situ from commercial Ti IV precursors, catalyze Barbiertype allylations, intramolecular crotylations (cyclizations), and prenylations of a wide range of aldehydes and ketones. The reaction displays surprising and unprecedented mechanistic subtleties. In cyclizations a fast and irreversible addition of an allyl radical to a TiIII-coordinated carbonyl group seems to occur. Intermolecular additions to conjugated aldehydes proceed through a coupling of a Ti IV-bound ketyl radical with an allyl radical. Reactions of ketones with allylic halides take place by the classical addition of an allylic organometallic reagent. The radical coupling processes enable transformations such as the highly regioselective α-prenylation that are otherwise difficult to achieve. The mild reaction conditions and the possibility to employ titanocene complexes in only catalytic quantities are highly attractive features of our protocol. These unusual properties have been taken advantage of for the straightforward synthesis of the natural products rosiridol, shikalkin, and 12-hydroxysqualene.
- Estevez, Rosa E.,Justicia, Jose,Bazdi, Btissam,Fuentes, Noelia,Paradas, Miguel,Choquesillo-Lazarte, Duane,Garcia-Ruiz, Juan M.,Robles, Rafael,Gansaeuer, Andreas,Cuerva, Juan M.,Oltra, J. Enrique
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experimental part
p. 2774 - 2791
(2009/12/03)
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- Evaluation of Chelation Effects Operative during Diastereoselective Addition of the Allylindium Reagent to 2- And 3-Hydroxycyclohexanones in Aqueous, Organic, and Mixed Solvent Systems
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The unprotected 2- and 3-hydroxycyclohexanones 1-8 were prepared by methods that skirted as much as possible their proclivity for α-ketol rearrangement (where the possibility for such isomerization exists). The diastereofacial selectivity of their reactio
- Paquette, Leo A.,Lobben, Paul C.
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p. 5604 - 5616
(2007/10/03)
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- Ligand effects in selective addition reactions of organoindium reagents with carbonyl compounds
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The reaction of the allyl indium sesquibromide (CH2 =CHCH2)3In2Br3 with four equivalents of a bulky lithium alkoxide ((CH3)3COLi or (CH3)3CCH2OLi) results in modified reagents which show unusual degrees of chemo-and stereoselectivity in reactions with carbonyl compounds. For example, in reactions with cyclohexanone derivatives, 84-93% equatorial attack with preferential formation of the axial alcohols is observed. Chiral aldehydes react in a highly diastereoselective manner.
- Reetz, Manfred T.,Haning, Helmut
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p. 117 - 120
(2007/10/03)
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- First preparation of allyl vanadium reagents in a mixed solvent of THF and HMPA (HMPA = hexamethylphosphoric triamide) and their application to allylation of carbonyl compounds
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Allylation of carbonyl compounds with allyl bromide mediated by a vanadium(II) complex in a mixed solvent of THF and HMPA (HMPA = hexamethylphosphoric triamide) has been accomplished. Coordination of HMPA to a vanadium metal is essential for the stabilization of the allyl vanadium species.
- Kataoka, Yasutaka,Makihira, Isamu,Tani, Kazuhide
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p. 7083 - 7086
(2007/10/03)
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- Indium in Organic Synthesis: Indium-Mediated Allylation of Carbonyl Compounds
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Indium-mediated allylation of a variety of ketones and aldehydes afforded excellent yields of the corresponding homoallylic alcohols under very mild reaction conditions.
- Araki, Shuki,Ito, Hirokazu,Butsugan, Yasuo
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p. 1831 - 1833
(2007/10/02)
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- Samarium(II) Di-iodide Induced Reductive Coupling of α,β-Unsaturated Esters with Carbonyl Compounds Leading to a Facile Synthesis of γ-Lactone
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Samarium(II) di-iodide, which is a strong one-electron transfer reducing agent, is effective for the reductive coupling of α,β-unsaturated esters with carbonyl compounds, whereby substituted γ-lactones can easily be prepared in good to excellent yields under very mild conditions.Two mole equiv. of samarium(II) di-iodide to each mole equiv. of starting substrate always give reasonable yields.The presence of an alcohol is essential in the reaction, complex unidentified products being formed in the absence of an alcohol; t-butyl alcohol gave more satisfactory results than methanol and ethanol.The alcohol acts as a proton donor, the use of MeOD leading to a deuteriated γ-lactone.The reaction is applicable to both aliphatic and aromatic ketones or aldehydes, whereas the electrochemical method is limited to aliphatic substrates.The diastereoselectivity is examined in the reaction of 4-t-butylcyclo-hexanone with ethyl acrylate; an anti-isomer is produced predominantly (syn:anti = 1:9) as the result of selective axial attack.The reaction may proceed by a radical mechanism, and reaction may not involve a samarium ester homoenolate.The reaction is extended to the intramolecular reaction of an α,β-unsaturated keto ester (8-oxonon-2-enoate) leading to the ready synthesis of a bicyclic γ-lactone.
- Fukuzawa, Shin-ichi,Nakanishi, Akira,Fujinami, Tatsuo,Sakai, Shizuyoshi
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p. 1669 - 1676
(2007/10/02)
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- Amphiphilic Reactions by Means of Exceptionally Bulky Organoaluminum Reagents. Rational Approach for Obtaining Unusual Equatorial, Anti-Cram, and 1,4 Selectivity in Carbonyl Alkylation
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Exceptionally bulky, oxygenophilic organoaluminum reagents, methylaluminum bis(2,6-di-tert-4-alkylphenoxide) (MAD and MAT), have been successfully utilized for stereoselective activation of carbonyl moiety.Combination of MAD or MAT with carbon nucleophiles such as organolithiums or Grignard reagents generates a new amphiphilic reaction system in which the alkylation may be interpreted as the nucleophilic addition of a reactive organometallic compound to an electrophilically activated carbonyl substrate in order to account for the regio- and stereochemical consequences.In contrast to the ordinary alkylations, the amphilic alkylation disclosed herein would be categorized into the new, yet unexplored class of alkylation that exhibits high chemoselectivity to carbonyl compounds, and more significantly it allows excellent equatorial and anti-Cram selectivity in carbonyl alkylations, hitherto difficult by the existing methodologies.Further, unusual conjugate addition of organolithium reagents to α,β-unsaturated carbonyl compounds has been accomplished by using the amphiphilic reaction system.
- Maruoka, Keiji,Itoh, Takayuki,Sakurai, Minoru,Nonoshita, Katsumasa,Yamamoto, Hisashi
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p. 3588 - 3597
(2007/10/02)
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- Stereoselective Addition of Organotitanium Reagents to Carbonyl Compounds
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Titanation of alkyllithium or -magnesium compounds using ClTi(OR)3 results in reagents which show markedly increased diastereofacial selectivity (80 - 90percent) in reactions with α-chiral aldehydes or ketones.Titanation is also the method of choice in Grignard-type additions to substituted cyclohexanones; CH3Ti(OCHMe2)3 (6a) adds predominantly from the equatorial direction, while allyltitanium reagents 11b and 12 show axial preference.Crotyltitanium compounds react with carbonyl compounds to afford primarily adducts having anti-configuration, a process which is of particular value in case of ketones (anti/syn ratios up to 99:1).Titanation of (trimethylsilyl)allyllithium (48) with Ti(OCHMe2)4 reverses regioselectivity in reactions with aldehydes and ketones, β-hydroxy silanes 50 being the only observed products.These have anti-configuration and can be converted either into Z- or E-dienes using the Peterson elimination under basic or acidic conditions, respectively.
- Reetz, Manfred T.,Steinbach, Rainer,Westermann, Juergen,Peter, Roland,Wenderoth, Bernd
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p. 1441 - 1454
(2007/10/02)
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- Highly Selective Carbon-Carbon Bond Forming Reactions Mediated by Chromium(II) Reagents
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A low valent chromium reagent is generated from chromium(III) chloride and a half mol of lithium aluminum hydride in tetrahydrofuran.The reagent behaves similarly to anhydrous chromium(II) chloride, which is commercially available, and reduces allylic halides to produce unisolable allylchromium species which add efficiently to aldehydes or ketones with high degree of stereo- and chemoselectivity.Particularly, high threo selectivity is observed in the reaction of aldehydes and 1-bromo-2-butene and is ascribed to a chair-like six-membered transition state.Simple reduction od allylic and benzylic halides produces biallyls and bibenzyls, while gem-dibromocyclopropanes afford the corresponding allenes in excellent yields.
- Hiyama, Tamejiro,Okude, Yoshitaka,Kimura, Keizo,Nozaki, Hitosi
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p. 561 - 568
(2007/10/02)
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The addition of allyl and butenyl Grignard reagents to 4-t-butylcyclohexanone affords a greater proportion of the equatorial alcohols than is formed from the corresponding saturated Grignard reagents (propyl and s-butyl). In the case of the allyl Grignard reagent, the equatorial alcohol is the major product. Lithium aluminium hydride reduction in ether at 0° of cis and trans 4-t-butyl-2-methyl-cyclohexanone and cis and trans 4-t-butyl-2-chlorocyclohexanone affords mixtures of epimeric alcohols in ratios of equatorial to axial OH 8.4:1, 20:1, 4.2:1, and >70:1 respectively. These results fit in well with the view that polar interactions and torsional strain are both important in determining the steric course of the reaction.
- Cherest
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p. 1593 - 1598
(2007/10/02)
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