- Lithiation reactions catalyzed by linear and cross-linked arene-based polymers. Generation of functionalized organolithium compounds
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Lithiation of various substrates, such as chlorinated acetals, α-chloro ether, dichloro derivatives benzo-fused heterocycles, and allyl and benzyl derivatives, with excess lithium powder in the presence of a catalytic amount of soluble linear or insoluble cross-linked arene (naphthalene or biphenyl)-based polymers yields the expected organolithium intermediates. The latter react with electrophiles either in two steps or under Barbier-type reaction conditions to afford the corresponding adducts. The catalyst is easily recuperated by filtration at the end of the process, and the procedure can be regarded as a reasonable alternative to the use of free arenes as electron carrier in lithiation reactions.
- Candela,Gomez,Yus
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- A ONE POT SYNTHESIS OF UNSYMMETRICAL SECONDARY ALCOHOLS FROM TWO GRIGNARD REAGENTS
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The sequential addition of two Grignard reagents to 2-(N-methyl-N-formyl)-amino-pyridine in tetrahydrofuran provides a high yield one pot synthesis of unsymmetrical secondary alcohols.
- Comins, Daniel L.,Dernell, William
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- Pd-Catalyzed Conjunctive Cross-Coupling between Grignard-Derived Boron “Ate” Complexes and C(sp2) Halides or Triflates: NaOTf as a Grignard Activator and Halide Scavenger
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Catalytic enantioselective conjunctive cross-couplings that employ Grignard reagents are shown to furnish an array of nonracemic chiral organoboronic esters in an efficient and highly selective fashion. The utility of sodium triflate in facilitating this reaction is two-fold: it enables “ate” complex formation and overcomes catalytic inhibition by halide ions.
- Lovinger, Gabriel J.,Aparece, Mark D.,Morken, James P.
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supporting information
p. 3153 - 3160
(2017/03/11)
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- Examining the origin of selectivity in the reaction of racemic alcohols with chiral N-phosphoryl oxazolidinones
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A range of known and novel N-phosphoryl oxazolidinones and imidazolidinones were prepared and screened in the kinetic resolution of a range of racemic magnesium chloroalkoxides. Models are proposed to account for the enantioselectivity achieved based on a combination of chiral relay effects, generation of transient stereochemistry and the structure of the intermediate magnesium alkoxide.
- Crook, Samuel,Parr, Nigel J.,Simmons, Jonathan,Jones, Simon
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p. 1298 - 1308
(2015/01/09)
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- Synthesis and application of benzyl-TMS derivatives as bench stable benzyl anion equivalents
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The regioselective benzylic metalation of toluenes using BuLi/KO tBu/TMP(H) (LiNK metalation conditions) and subsequent transmetalation to Si by reaction with TMSCl provides a general one-pot procedure for the synthesis of substituted benzyltrimethylsilanes. ArCH 2Si(Me)3 derivatives are bench stable reagents yet can serve as benzyl anion equivalents under mild reaction conditions. Following activation with fluoride they can successfully participate in a wide range of additions to both non-enolizable and enolizable carbonyls. In addition, their use in the synthesis of isochromanones and trifluoromethylated amines is illustrated. The broad synthetic scope and mild practical conditions of use for ArCH2Si(Me)3 reagents demonstrate their general potential as benzyl anion equivalents.
- Das, Manas,O'Shea, Donal F.
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p. 6448 - 6460
(2013/07/26)
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- Pivaloylmetals (tBu-COM: M=Li, MgX, K) as equilibrium components
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Short-lived pivaloylmetals, (H3C)3C-COM, were established as the reactive intermediates arising through thermal heterolytic expulsion of O=CtBu2 from the overcrowded metal alkoxides tBuC(=O)-C(-OM)tBu2 (M=MgX, Li, K). In all three cases, this fission step is counteracted by a faster return process, as shown through the trapping of tBu-COM by O=C(tBu)-C(CD3)3 with formation of the deuterated starting alkoxides. If generated in the absence of trapping agents, all three tBu-COM species "dimerize" to give the enediolates MO-C(tBu)=C(tBu)-OM along with O=CtBu2 (2 equiv). A common-component rate depression by surplus O=CtBu2 proves the existence of some free tBu-COM (separated from O=CtBu2); but companion intermediates with the traits of an undissociated complex such as tBu-COM & O=CtBu2 had to be postulated. The slow fission step generating tBu-COMgX in THF levels the overall rates of dimerization, ketone addition, and deuterium incorporation. Formed by much faster fission steps, both tBu-COLi and tBu-COK add very rapidly to ketones and dimerize somewhat slower (but still fairly fast, as shown through trapping of the emerging O=CtBu2 by H3CLi or PhCH2K, respectively). At first sight surprisingly, the rapid fission, return, and dimerization steps combine to very slow overall decay rates of the precursor Li and K alkoxides in the absence of trapping agents: A detailed study revealed that the fast fission step, generating tBu-COLi in THF, is followed by a kinetic partitioning that is heavily biased toward return and against the product-forming dimerization. Both tBu-COLi and tBu-COK form tBu-CH=O with HN(SiMe3)3, but only tBu-COK is basic enough for being protonated by the precursor acyloin tBuC(=O)-C(-OH)tBu2. Copyright
- Knorr,Boehrer,Schubert,Boehrer
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experimental part
p. 7506 - 7515
(2012/07/27)
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- Multifaceted palladium catalysts towards the tandem diboration-arylation reactions of alkenes
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Novel Pd26+ compounds have been synthesized in high yield. These compounds and their Pd24+ counterparts as synthetic precursors mediate the diboration of vinylarenes and aliphatic 1-alkenes, and under mild and basic reaction conditions they produce a variety of 1,2-diboronate esters with excellent conversions and chemo-selectivities. The presence of bis(catecholato)diboron (B2cat2) favours the reduction of PdIII to PdII, while the catalytic precursor of PdII is transformedinto Pd0-nanoparticles. An "in situ" catalytic tandem reaction has been designed to transform the diboronate intermediates into the monoarylated product, which after oxidative workup, provides the carbohydroxylated adduct. Eventually, the same catalyst performs both sequences with total conversion from the alkene.
- Penno, Dirk,Lillo, Vanesa,Koshevoy, Igor O.,Sanau, Mercedes,Ubeda, M. Angeles,Lahuerta, Pascual,Fernandez, Elena
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supporting information; experimental part
p. 10648 - 10655
(2009/12/01)
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- Functionalized benzylic magnesium reagents through a sulfur-magnesium exchange
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(Chemical Equation Presented) Switch it: lodobiphenyl thioethers readily undergo an iodine-magnesium exchange followed by, after the addition of tBuOLi, an intramolecular sulfur-magnesium exchange, which provides benzylic magnesium reagents in excellent yield through a fragmentation reaction.
- Stoll, Armin H.,Krasovskiy, Arkady,Knochel, Paul
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p. 606 - 609
(2007/10/03)
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- Direct transformation of allylic and benzylic thiols, thioethers, and disulfides into organolithium compounds
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The reaction of allylic and benzylic thiols 1, disulfides 3, and thioethers 4 and 5 with an excess of lithium and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 5mol%) afforded the corresponding allylic and benzylic organolithium reagents via reductive cleavage of the carbon-sulfur bond. The generated organolithium compounds gave the expected products 2 by reaction with several electrophiles followed by hydrolysis with water. The reaction conditions and the lithiation procedure (stepwise of Barbier-type process) depended on the starting sulfur containing compound.
- Yus, Miguel,Martinez, Pedro,Guijarro, David
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p. 2365 - 2376
(2007/10/03)
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- Generation of allylic and benzylic organolithium compounds by fluorine-lithium exchange: Reaction with electrophiles
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The application of the naphthalene-catalysed lithiation methodology to allylic and benzylic fluorides 1 led to the corresponding allylic and benzylic organolithium reagents, which, in the presence of different electrophiles (Barbier-type reaction conditions), afforded the expected products 2 in moderate yields. The procedure was useful for the transformation of primary, secondary and tertiary benzylic fluorides into the corresponding lithium derivatives. When a two-step lithiation process was used (treatment of fluoride 1 with lithium and a catalytic amount of naphthalene, followed by addition of the electrophilic reagent), only Wurtz-type coupling products were formed.
- Guijarro, David,Yus, Miguel
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- Generation of allylic and benzylic organolithium reagents from the corresponding ester, amide, carbonate, carbamate and urea derivatives
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The reaction of different allylic and benzylic non-enolisable esters or amides (1), carbonates (4), carbamates (6, 7) and ureas (8) with an excess of lithium powder and a catalytic amount of naphthalene (10%) in the presence of an electrophile [(i)PrCHO, (t)BuCHO, PhCHO, Me2CO, Et2CO, (CH2)5CO, Ph2CO, Me3SiCl] in THF at different temperatures (-78, -30 or 0°C) leads, after hydrolysis with water to the corresponding allylated or benzylated products (2).
- Alonso, Emma,Guijarro, David,Martinez, Pedro,Ramon, Diego J.,Yus, Miguel
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p. 11027 - 11038
(2007/10/03)
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- Reductive lithiation of arylalkyl methyl ethers
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We have investigated the reductive cleavage of arylalkyl methyl ethers with an excess of lithium metal and a catalytic amount of naphthalene. The reaction proceeds regioselectively in the presence of various substituents on the aromatic ring, allowing access to a wide array of arylalkyl lithium derivatives some of which are not easily accessible by conventional methods.
- Azzena, Ugo,Carta, Simonetta,Melloni, Giovanni,Sechi, Alessandra
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p. 16205 - 16212
(2007/10/03)
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- Intramolecular Reactivity of Arylcarbenes: Derivatives of o-Tolylcarbene
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Various CH2X groups have been attached to the ortho position of phenylcarbene.If 2'- or 3'-C-H bonds are present, as in 23 (X = Me), 71 (X = CMe3), and 58 (X = SiMe3), C-H insertion leading to five- or six-membered rings predominates in the gas phase and competes with intermolecular reactions in solution.The formation of benzocyclobutenes via insertion into 1'-C-H bonds is a very minor reaction path of 23 and 71.In contrast, 58 produces substantial amounts of the benzocyclobutene 59 by way of C-Si insertion, particularly in the gas phase.Insertion into the Si-Me bonds of 58 also occurs while the C-F bonds of 37 (X = CF3) and 50 (X = F) are inert.In the gas phase, 37 and 50 give mainly benzocyclobutenes whereas intermolecular reactions prevail in solution.The effects of sensitization and of solvent polarity suggest that benzocyclobutenes arise from singlet arylcarbenes.The amount of carbene-carbene rearrangement decreases in the order 7 (X = H) > 37 (X = CF3) > 23 (X = Me); no rearrangement was observed with 50 (X = F), 58 (X = SiMe3), and 71 (X = CMe3).
- Kirmse, Wolfgang,Konrad, Wolfgang,Schnitzler, Dirk
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p. 3821 - 3829
(2007/10/02)
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