- 1,2-Dibromotetrachloroethane: An efficient reagent for many transformations by modified Appel reaction
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An efficient and facile method has been developed for the synthesis of alkyl bromides from various alcohols under mild conditions using a triphenylphosphine (PPh 3) /1,2-dibromotetrachloroethane (DBTCE) complex in excellent yields and very short time (5 min). This method can also be applied for the transformation of chiral alcohols to their corresponding bromides in very high enantiomeric excess. The PPh 3 /DBTCE complex is also successfully applied to ring-opening reactions of cyclic ethers in mild conditions. Esterification, amidation, and formation of acid anhydrides under very mild experimental conditions are also successfully accomplished by following a modification of the Appel reaction protocol in this work.
- Essiz, Sel?uk,Da?tan, Arif
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p. 150 - 156
(2019/05/16)
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- (-)-Menthol as a source of new N,N-diamine ligands for asymmetric transfer hydrogenation
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The synthesis of new chiral N-monotosylated-1,2-diamines based on the (-)-menthol skeleton is presented. The elimination of HCl from neomenthyl chloride obtained from an Appel reaction led to p-menth-3-ene in excellent yield. Further functionalization of the double bond in p-menth-3-ene with chloramine-T gave the corresponding N-tosylaziridines, which upon reaction with sodium azide and subsequent reduction of the azide functional group, formed the 1,2-diamine system. The synthesized chiral ligands proved effective in the asymmetric transfer hydrogenation of aromatic ketones and an endocyclic imine.
- Roszkowski, Piotr,Maurin, Jan K.,Czarnocki, Zbigniew
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supporting information
p. 2184 - 2188
(2018/05/07)
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- M -C2B10H11HgCl/AgOTf-Catalyzed Reaction for Reductive Deoxygenation
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A m -C2B10H11HgCl/AgOTf-catalyzed reaction of allyl silyl ethers with N -Boc- N ′-tosylhydrazine has been developed. Under mild conditions, the resulting allyl hydrazine products were transformed into naked alkenes in good yield. Furthermore, the used m -C2B10H11HgCl could be recovered quantitatively.
- Yamasaki, Naoto,Kanno, Marina,Sakamoto, Kyohei,Kasai, Yusuke,Imagawa, Hiroshi,Yamamoto, Hirofumi
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p. 169 - 175
(2018/03/26)
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- Stereochemistry of the Menthyl Grignard Reagent: Generation, Composition, Dynamics, and Reactions with Electrophiles
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Menthyl Grignard reagent 1 from either menthyl chloride (2) or neomenthyl chloride (3) consists of menthylmagnesium chloride (1a), neomenthylmagnesium chloride (1b), trans-p-menthane (4), 2-menthene (8), 3-menthene (9), and Wurtz coupling products including symmetrical bimenthyl 13. The diastereomeric ratio 1a/1b was determined in situ by 13C NMR or after D2O quenching by 2H NMR analysis. Hydrolysis of the C-Mg bond proceeds with retention of configuration at C-1. The kinetic ratio 1a/1b from Grignard reagent generation (dr 59:41 at 50 °C in THF) is close to the thermodynamic ratio (56:44 at 50 °C in THF). Carboxylation of 1 at -78 °C separates diastereomers 1a/b to give the anion of menthanecarboxylic acid (19) from 1a, which combines with unreactive 1b to give neomenthylmagnesium menthanecarboxylate (1bI). The kinetics of epimerization for the menthyl/neomenthylmagnesium system was analyzed (ΔH? = 98.5 kJ/mol, ΔS? = -113 J/mol·K for 1bI → 1aI). Reactions of 1 with phosphorus electrophiles proceed stereoconvergently at C-1 of 1a/b to give predominantly menthyl-configured substitution products: PCl3 and 2 equiv of 1 give Men2PCl (6), which hydrolyzes to dimenthylphosphine P-oxide (7), whereas Ph2PCl with 1 equiv of 1 gave P-menthyldiphenylphosphine oxide (27) after workup in air.
- Koller, Sebastian,Gatzka, Julia,Wong, Kit Ming,Altmann, Philipp J.,P?thig, Alexander,Hintermann, Lukas
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p. 15009 - 15028
(2019/01/03)
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- Synthesis and sensory studies of umami-active scaffolds
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The class of 2-isopropyl-5-methylbicyclo[4.1.0]heptane-7-carboxamides, 1-4, has been identified as potent umami-tasting molecules. A scalable synthesis of this challenging scaffold and new sensory insights will be presented. Interestingly, the umami chara
- Backes, Michael,Paetz, Susanne,V?ssing, Tobias,Ley, Jakob Peter
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p. 1782 - 1797
(2015/02/19)
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- Copper(I)-catalyzed boryl substitution of unactivated alkyl halides
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Borylation of alkyl halides with diboron proceeded in the presence of a copper(I)/Xantphos catalyst and a stoichiometric amount of K(O-t-Bu) base. The boryl substitution proceeded with normal and secondary alkyl chlorides, bromides, and iodides, but alkyl sulfonates did not react. Menthyl halides afforded the corresponding borylation product with excellent diastereoselectivity, whereas (R)-2-bromo-5-phenylpentane gave a racemic product. Reaction with cyclopropylmethyl bromide resulted in ring-opening products, suggesting the reaction involves a radical pathway.
- Ito, Hajime,Kubota, Koji
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scheme or table
p. 890 - 893
(2012/05/05)
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- Radical chain reduction of alkylboron compounds with catechols
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The conversion of alkylboranes to the corresponding alkanes is classically per-formed via protonolysis of alkylboranes. This simple reaction requires the use of severe reaction conditions, that is, treatment with a carboxylic acid at high temperature (>150 °C). We report here a mild radical procedure for the transformation of organoboranes to alkanes. 4-tert-Butylcatechol, a well-established radical inhibitor and antioxidant, is acting as a source of hydrogen atoms. An efficient chain reaction is observed due to the exceptional reactivity of phenoxyl radicals toward alkylboranes. The reaction has been applied to a wide range of organoboron derivatives such as B- alkylcatecholboranes, trialkylboranes, pinacolboronates, and alkylboronic acids. Furthermore, the so far elusive rate constants for the hydrogen transfer between secondary alkyl radical and catechol derivatives have been experimentally determined. Interestingly, they are less than 1 order of magnitude slower than that of tin hydride at 80 °C, making catechols particularly attractive for a wide range of transformations involving C-C bond formation.
- Villa, Giorgio,Povie, Guillaume,Renaud, Philippe
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p. 5913 - 5920
(2011/06/16)
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- Microwave-assisted ester formation using O-alkylisoureas: A convenient method for the synthesis of esters with inversion of configuration
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(Chemical Equation Presented) The formation of carboxylic esters via reaction of carboxylic acids with O-alkylisoureas proceeds in excellent yields with very short reaction times when conducted in a monomode microwave synthesizer. Efficient processes were
- Chighine, Alessandra,Crosignani, Stefano,Arnal, Marie-Claire,Bradley, Mark,Linclau, Bruno
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experimental part
p. 4753 - 4762
(2009/10/17)
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- Clarification of the stereochemical course of nucleophilic substitution of arylsulfonate-based nucleophile assisting leaving groups
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(Chemical Equation Presented) Secondary alcohols modified as tosylates, PEG-sulfonates, or quisylates undergo inversion of configuration at the reacting center when treated with lithium halide in acetone at reflux, where the PEG-sulfonates and quisylates are substantially more reactive. In sterically hindered cases, elimination is a competing process. In contrast, when treated with TiCl4, simple secondary sulfonates give chloride products with partial inversion of configuration. Any observed retention of configuration in a given alkyl sulfonate substrate under these conditions is likely due to neighboring group participation or diastereoselective attack on a carbocation (or ion pair) rather than an SNi mechanism.
- Braddock, D. Christopher,Pouwer, Rebecca H.,Burton, Jonathan W.,Broadwith, Phillip
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experimental part
p. 6042 - 6049
(2009/12/24)
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- O-DPPB-directed copper-mediated and -Catalyzed allylic substitution with grignard reagents
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The ortho-diphenylphosphanylbenzoyl (o-DPPB) group was explored as a directing leaving group in copper-mediated and copper-catalyzed allylic substitution with Grignard reagents. Complete control of chemo-, regio- and stereoselectivity with complete syn-1,3-chirality transfer was observed as a result of the directed nature of the reaction. No excess of or ganometallic reagent is required and the directing group can be recovered quantitatively. Coordination studies in the solid state and in solution have shown that two substrates are bound via the phosphine function of the directing group at copper. Dynamic NMR experiments in solution are in agreement with a ligand-exchange process at copper, a prerequisite for the development of a substoichiometric process.
- Demel, Peter,Keller, Manfred,Breit, Bernhard
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p. 6669 - 6683
(2008/09/16)
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- The Hendrickson reagent and the Mitsunobu reaction: A mechanistic study
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The alkoxytriphenylphosphonium ion intermediate of the Mitsunobu reaction can be generated using the Hendrickson reagent, triphenylphosphonium anhydride trifluoromethanesulfonate, 1. Strangely, while the reagent 1 can be used in place of the Mitsunobu reagents (triphenylphosphine and a dialkylazodicarboxylate) for the esterification of primary alcohols, secondary alcohols such as menthol undergo elimination. Evidence is presented to show that this unexpected result is due to the presence of trialkylammonium triflate salts. Such salts lead to a dramatic decrease in the rate of esterification relative to competing elimination. The Mitsunobu esterification of menthol with p-nitrobenzoic acid was re-examined and the occurrence of elimination reported for the first time. The presence of traces of tetrabutylammonium triflate led to a dramatic reduction in the yield of inverted ester and a corresponding increase in the yield of anti elimination product 2-menthene. The mechanism of the Mitsunobu reaction is discussed in the light of the dramatic salt effect on both the rate and outcome of the reaction and the possible involvement of ion pair clustering. In contrast, use of the reagent 1 resulted in syn elimination to give a 1:2 mixture of 2- and 3-menthenes. Finally, 1 and sodium azide can be used to convert a primary alcohol into an azide in high yield. There was no reaction under Mitsunobu conditions.
- Elson, Kathryn E.,Jenkins, Ian D.,Loughlin, Wendy A.
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p. 2958 - 2965
(2007/10/03)
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- Copper-Mediated and -Catalyzed o-DPPB-Directed Allylic Substitution
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Complete control of chemo-, regio- and stereoselectivity in the course of copper-catalyzed and -mediated allylic substitution could be obtained with me ortho-diphenylphosphanyl (o-DPPB) function as a reagent-directing leaving group. Complete chirality transfer by way of a syn-addition process has been achieved for cyclic and acyclic systems. Readily available Grignard reagents may be employed as nucleophiles and the directing o-DPPB group can be recovered quantitatively. The reaction requires neither cooling nor an excess of organometallic reagent.
- Breit, Bernhard,Demel, Peter
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p. 429 - 432
(2007/10/03)
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- Chloromethanesulfonate as an efficient leaving group: Rearrangement of the carbon-carbon bond and conversion of alcohols into azides and nitriles
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The chloromethanesulfonate (monochlate) served as an efficient leaving group for rearrangement of the carbon-carbon bond and conversion of alcohols into azides and nitriles. The treatment of the monochlate 16a with zinc acetate in dioxane at 90 °C effected migration of the 4α-methyl group to give alkene 17a. Upon similar treatment of the monochlates 22a, 25a, 28a, and 31a with zinc acetate, the carbon-carbon bonds antiperiplanar to the hydroxyl groups efficiently migrated to afford the alkenes 23a, 26a-c, 29a,b, and 32a, respectively. In the case of the diol 40, the monochlate was converted into the ketone 41 via a rearrangement-ring expansion. The reaction of the monochlates 44a, 47a, 49a, 52a, and 57a with sodium azide or lithium azide in N,N-dimethylformamide efficiently afforded the azides with inversion of the configuration. The introduction of a nitrile group to the sterically hindered alcohol 59 was performed in high yield by the reaction of the monochlate 60a with sodium cyanide.
- Shimizu, Takeshi,Ohzeki, Tomoya,Hiramoto, Katsuya,Hori, Nobuyuki,Nakata, Tadashi
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p. 1373 - 1385
(2007/10/03)
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- One-step conversion of protected alcohols into alkyl halides using dimethylphosgeniminium salt
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Efficient conversion of tetrahydro-2-pyranyl (THP)protected alcohols into the corresponding halides using dichlorophosgeniminium chloride in the presence of tetraalkylammonium halide.
- Schlama,Gouverneur,Mioskowski
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p. 3517 - 3520
(2007/10/03)
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- Efficient method for inversion of secondary alcohols by reaction of chloromethanesulfonates with cesium acetate
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Inversion of a variety of secondary alcohols using the (chloromethylsulfonyl)oxy group as a favorable leaving group with cesium acetate in the presence of 18-crown-6 has been performed to give the inverted acetates in high yields.
- Shimizu, Takeshi,Hiranuma, Sayoko,Nakata, Tadashi
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p. 6145 - 6148
(2007/10/03)
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- ALYLATION OF ALLYLIC CYCLOHEXENYL ESTERS WITH TRIALKYLALUMINIUM REAGENTS. A REGIO AND STEREOCHEMICAL STUDY
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Regio and stereochemistry of the title reaction appear to be strongly influenced by the nature of both organometallic and allylic reagents.The results are discussed in view of the intervention of ion-pair intermediates.
- Gallina, C.
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p. 519 - 522
(2007/10/02)
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- REGIO AND STEREOSPECIFIC SYNTHESIS OF CIS AND TRANS 3-METHYL-6-METHYLETHYL CYCLOHEXENES AND 3-METHYL-4-METHYLETHYLCYCLOHEXENES. REACTIONS OF ALLYLIC ACETATES AND CARBAMATES WITH Li2Cu3Me5 AND LiCuMe2
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The isomeric alkenes 1-4 have been obtained by syn, γ substitution of the appropriate allylic carbamates with Li2Cu3Me5.The behaviour of carbamates is deeply affected by the nature of the copper reagent.
- Gallina, C.
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p. 3093 - 3096
(2007/10/02)
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