- The influence of α-coordinating groups of aldehydes on E/Z-selectivity and the use of quaternary ammonium counter ions for enhanced E-selectivity in the Julia–Kocienski reaction
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Modified reaction conditions for improved E-selectivity of olefins in the Julia–Kocienski reaction of aldehydes having α-coordinating substituents are demonstrated. The chelating groups in aldehydes are expected to stabilize the syn-transition state with metal ions, whereas the weakly coordinating quaternary ammonium ions are devoid of all possible chelating interactions to enhance E-selectivity. A systematic investigation is presented to study the size of the neighbouring protecting groups of aldehydes and their chelation effect on E/Z-selectivity in the Julia–Kocienski reaction.
- Rehman, Mintu,Surendran, Sravya,Siddavatam, Nagendra,Rajendar, Goreti
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supporting information
p. 329 - 333
(2022/01/20)
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- Kinetic Resolution of Allylic Alcohol with Chiral BINOL-Based Alkoxides: A Combination of Experimental and Theoretical Studies
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The development and characterization of enantioselective catalytic kinetic resolution of allylic alcohols through asymmetric isomerization with chiral BINOL derivatives-based alkoxides as bifunctional Br?nsted base catalysts were described in the study. A number of chiral BINOL derivatives-based alkoxides were synthesized, and their structure-enantioselectivity correlation study in asymmetric isomerization identified a promising chiral Br?nsted base catalyst, which afforded various chiral secondary allylic alcohols (ee up to 99%, S factor up to >200). In the mechanistic study, alkoxide species were identified as active species and the phenol group of BINOL largely affected the high reactivity and enantioselectivity via hydrogen bonding between the chiral Br?nsted base catalyst and substrates. The strategy is the first successful synthesis strategy of various chiral secondary allylic alcohols through enantioselective transition-metal-free base-catalyzed isomerization. The applicability of the strategy had been demonstrated by the synthesis of the bioactive natural product (+)-veraguensin.
- Liu, Yidong,Liu, Song,Li, Dongmei,Zhang, Nan,Peng, Lei,Ao, Jun,Song, Choong Eui,Lan, Yu,Yan, Hailong
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p. 1150 - 1159
(2019/01/11)
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- Synthesis of Highly Substituted Furans by a Cascade of Formal anti-Carbopalladation/Hydroxylation and Elimination
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Highly substituted furans are generated by a cascade of formal anti-carbopalladation, attack of a nucleophilic hydroxy group, and aromatization by elimination of the emerging dihydrofuran derivative. Mono-, di-, and trisubstituted furans were obtained in good to excellent yields. When we attempted to access tetrasubstituted furan derivatives, an additional rearrangement was observed that resulted in the formation of chromenes. Follow-up chemistry shows the utility of TMS as a protecting group for the alkyne moiety.
- Schitter, Theresa,Roy, Naveen J.,Jones, Peter G.,Werz, Daniel B.
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supporting information
p. 640 - 643
(2019/02/05)
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- Enantioselective aerobic oxidation of α-hydroxy-ketones catalyzed by oxidovanadium(V) methoxides bearing chiral, N-salicylidene- tert -butylglycinates
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Chiral oxidovanadium(V) methoxides prepared from 3,5-disubstituted-N- salicylidene-l-tert-butylglycines and vanadyl sulfate in air-saturated MeOH serve as highly enantioselective catalysts for asymmetric aerobic oxidations and kinetic resolution of alkyl, aryl, and heteroaryl α-hydroxy-ketones with differed α-substituents at ambient temperature in toluene or TBME (tert-butyl methyl ether). The best scenarios involve the use of complexes which bear the tridendate templates derived from 3,5-diphenyl- or 3-o-biphenyl-5-nitro-salicyaldehyde. The kinetic resolution selectivities of the aerobic oxidation process are in the range of 12 to >1000 based on the selectivity factors (krel).
- Chen, Chien-Tien,Kao, Jun-Qi,Salunke, Santosh B.,Lin, Ya-Hui
-
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- β-fluoroamphetamines via the stereoselective synthesis of benzylic fluorides
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A range of substituted aryl epoxides undergo efficient ring-opening hydrofluorination upon treatment with 0.33 equiv of BF3-OEt 2 in CH2Cl2 at -20 -°C to give the corresponding syn-fluorohydrins, consistent with a mechanism involving a stereoselective SN1-type epoxide ring-opening process. The benzylic fluoride products of these reactions are valuable templates for further elaboration, as demonstrated by the preparation of a range of aryl-substituted β-fluoroamphetamines.
- Cresswell, Alexander J.,Davies, Stephen G.,Lee, James A.,Roberts, Paul M.,Russell, Angela J.,Thomson, James E.,Tyte, Melloney J.
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supporting information; experimental part
p. 2936 - 2939
(2010/09/10)
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- A convenient and versatile method for the preparation of α-hydroxymethyl ketone derivatives from the corresponding allyl silyl ethers or allyl carboxylates
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The ozonolysis of 1-substituted allyl silyl ethers or 1-substituted allyl carboxylates followed by treatment with bases gave the corresponding α-silyloxymethyl- or α-acyloxymethyl-ketones in good yields. It is proposed to proceed via the corresponding α-silyloxy- or α-acyloxyaldehydes intermediates followed by 1,4-group migration. The results of theoretical calculations are applicable to explain the experimental results.
- Hon, Yung-Son,Wong, Ying-Chieh,Wu, Kuo-Jui
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experimental part
p. 896 - 914
(2009/12/06)
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- Ether-directed diastereoselectivity in catalysed Overman rearrangement: comparative studies of metal catalysts
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Ether-directed diastereoselectivity in Overman rearrangement of δ-methoxy and δ-TBDMSO substituted allylic trichloroacetimidates has been explored using PtCl2, PtCl4, AuCl and AuCl3 catalysts in comparison with commonly us
- Jaunzeme, Ieva,Jirgensons, Aigars
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p. 5794 - 5799
(2008/09/21)
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- Synthesis of 3-fluorofuran-2(5H)-ones based on Z/E photoisomerisation and cyclisation of 2-fluoro-4-hydroxybut-2-enoates
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Mixtures of some (E)- and (Z)-2-fluoroalk-2-enoates prepared from the corresponding 2-hydroxycarbonyl compounds and ethyl 2-(diethoxyphosphoryl)-2- fluoroacetate have been transformed in high conversions into the target 3-fluorofuran-2(5H)-ones by an effi
- Pomeisl, Karel,Cejka, Jan,Kvicala, Jaroslav,Paleta, Oldrich
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p. 5917 - 5925
(2008/04/13)
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- Tishchenko reactions of aldehydes promoted by diisobutylaluminum hydride and its application to the macrocyclic lactone formation
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Aliphatic aldehydes react with catalytic amount of Dibal-H in n-pentane to give the corresponding Tishchenko products in good to excellent yields. On contrary, α-silyloxy aldehydes give α-silyloxy ketones via Oppenauer oxidation under similar condition. Tishchenko reaction of ω-alkene aldehydes followed by RCM and hydrogenation affords a convenient method to prepare the 11-37 membered macrocyclic lactones.
- Hon, Yung-Son,Wong, Ying-Chieh,Chang, Chun-Ping,Hsieh, Cheng-Han
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p. 11325 - 11340
(2008/03/12)
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- Synthetic applications of the amine-base treatment in the ozonolysis of substituted-allyl silyl ethers or -allyl esters via a novel ene-diol type rearrangement
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The ozonolysis of substituted-allyl silyl ethers or -allyl esters followed by treatment with bases gave the corresponding α-silyloxy ketones or α-acyloxy ketones in good yields. The reaction is proposed to proceed via a novel ene-diol rearrangement of the corresponding α-silyloxy aldehydes or α-acyloxy aldehydes intermediates.
- Hon, Yung-Son,Wong, Ying-Chieh
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p. 1365 - 1368
(2007/10/03)
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- A Silicon Tether Approach for Addition of Functionalized Radicals to Chiral α-Hydroxyhydrazones: Diastereoselective Additions of Hydroxymethyl and Vinyl Synthons
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Stereocontrolled additions of hydroxymethyl and vinyl groups to chiral α-hydroxyhydrazones can be achieved by radical cyclizations using bromomethyl or vinyl radical precursors tethered via a temporary silicon connection. Tin-mediated 5-exo radical cycliz
- Friestad, Gregory K.,Massari, Sara E.
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p. 863 - 875
(2007/10/03)
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- Remote substituent effect favoring the formation of syn-adducts in the chelation controlled radical reactions of γ-benzyloxy-α-methylenecarboxylic acid esters
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The chelation controlled radical reactions of ethyl γ-benzyloxy-α-methylenecarboxylates bearing a bulky γ-substituent, such as CHMe2, CHPh2, c-C6H11 and CH(Ph)OTBDMS, with alkyl iodides gave the syn-adducts with high diastereoselectivities. However, the diastereoselectivity for the substrates bearing a γ-substituent CH(i-Pr)OTBDMS depended critically on the configuration of the substituent; the substrate bearing the OTBDMS group anti to the γ-benzyloxy group showed poor diastereoselectivity, but its diastereomer gave syn-adduct exclusively. The high syn-selectivitiy is referred to the H-atom transfer to the outside face of radical center in the sharply folded seven-membered chelate intermediate bearing the ethoxy group with Z-geometry. The corner flapping of the radical center atom of the global minimum energy conformer generates a local minimum conformer and the H-atom transfer to the outside face of the radical center of the newly formed structure gives the anti-adduct. The poor diastereoselectivity is due to the very small energy difference between the two conformers and consequently both the syn- and anti-adducts are yielded in nearly equal amounts.
- Nagano, Hajime,Ohkouchi, Hisako,Yajima, Tomoko
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p. 3649 - 3663
(2007/10/03)
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- Comparative Study of the Diastereoselective Addition of Allenyl Zinc Reagents to α-Alkoxy (or Silyloxy) Aldehydes and Imines. A Straightforward Synthesis of Amino Alcohols from Imines
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The addition of allenylzinc bromides to α-chiral imines proceeds with very high diastereoselectivity. This result is in contrast with the addition to the corresponding aldehydes, leading to poor diastereoselectivity. The anti/anti adducts are explained by Felkin-Ahn and Gaudemar-Yamamoto models of the transition state.
- Poisson, Jean-Francois,Normant, Jean F.
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p. 6553 - 6560
(2007/10/03)
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- A silicon tether approach for diastereocontrol in radical addition to chiral hydrazones
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(formula presented) A radical carbon-carbon bond construction approach to chiral α-branched amines is presented. Stereocontrolled radical addition to chiral hydrazones can be achieved by virtue of conformational constraints imposed during cyclizations usi
- Friestad, Gregory K.
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p. 1499 - 1501
(2008/02/09)
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- Highly Diastereoselective Conjugate Addition of Lithium Dialkylamides to α,β-Unsaturated Esters Having a Chiral Center at the γ-Position
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The conjugate addition of lithium amides 2 to tert-butyl 4-(OR)-substituted-2-pentenoates 1 produced a mixture of the syn- and anrt-amino esters (3 and 4) in high yields. Sterically bulky OR groups, such as trityloxy and tert-butyldiphenylsilyloxy, gave t
- Asao, Naoki,Shimada, Takashi,Sudo, Tomoko,Tsukada, Naofumi,Yazawa, Kazuhiko,Gyoung, Young Soo,Uyehara, Tadao,Yamamoto, Yoshinori
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p. 6274 - 6282
(2007/10/03)
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- Reduction of α-Trialkylsiloxy Nitriles with Diisobutylaluminium Hydride (DIBAH): A Facile Preparation of α-Trialkylsiloxy Aldehydes and their Derivatives
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The stepwise synthesis of α-trimethylsiloxy aldehydes and α-hydroxy aldehydes could be achieved via the reduction of α-trimethylsiloxy nitriles with diisobutylaluminium hydride (DIBAH) starting from a variety of ketones.The facile synthesis of optically active α-tert-butyldimethylsiloxy aldehydes was attained by combination of asymmetric silylcyanation of aldehydes and DIBAH reduction of optically active α-siloxy nitriles.Furthermore, in the reduction of some α-tert-butyldimethylsiloxy-β,γ-unsaturated nitriles, migration of the double bond took place to form more stable α-siloxy-α,β-unsaturated aldehydes under some reaction conditions.
- Hayashi, Masahiko,Yoshiga, Tomoko,Nakatani, Kanako,Ono, Kazuyuki,Oguni, Nobuki
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p. 2821 - 2830
(2007/10/02)
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- Mechanistic insight into the cinnamylmetal-thioacetal reaction employing 2-acetoxy-2-phenylacetaldehyde monothioacetal
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The reaction of 2-acetoxy-2-phenylacetaldehyde monothioacetal with cinnamylsilane and -tin serves as a model system for disclosing the simple diastereoselectivity of unambiguously assigned SN1- and SN2-like reactions between thioacet
- Sato, Tsuneo,Otera, Junzo
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