35242-05-8Relevant academic research and scientific papers
Enantioselective Hydroazidation of Trisubstituted Non-Activated Alkenes
Meyer, Daniel,Renaud, Philippe
, p. 10858 - 10861 (2017/08/30)
A one-pot procedure for the enantioselective hydroazidation of non-activated trisubstituted alkenes is described. Hydroboration with monoisopinocampheylborane (IpcBH2) provides dialkylboranes that are in situ selectively converted into monoalkyl-substituted catecholboranes; these undergo radical azidation upon treatment with benzenesulfonyl azide and a radical initiator. Enantiomerically enriched azides were thus obtained in yields of 59–81 % and enantioselectivities of up to 94:6 e.r. (98:2 e.r. if the intermediate dialkylborane is purified by crystallization). A rapid access to enantiomerically pure (+)-rodocaine is also described. The use of other arenesulfonyl radical traps enables enantioselective hydroallylation, hydrosulfanylation, and hydrobromination reactions with yields of 71–86 %.
Regioselective SN2 opening of vinylic epoxides with trialkylzincates and trialkylaluminates
Equey, Olivier,Vrancken, Emmanuel,Alexakis, Alexandre
, p. 2151 - 2159 (2007/10/03)
The use of trialkylorganozincates and tetraalkylaluminates allows regioselective SN2 nucleophilic opening of vinylic epoxides. The reaction occurs with an anti-substitution pattern and can be applied to a wide range of substrates. We also show that the solvent and the structure of the epoxide have an influence on the substitution products' ratio. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
Conformational effects on lipase-mediated acylations of 2-substituted cyclohexanols
Tanikaga, Rikuhei,Matsumoto, Yoshimasa,Sakaguchi, Maki,Koyama, Yohei,Ono, Kentaro
, p. 6781 - 6783 (2007/10/03)
Lipase-mediated acetylations of trans- and cis-2-substituted cyclohexanols gave the corresponding (1R)-cyclohexyl acetates and (1S)-cyclohexanols in high yields and ee, but c-4-tert-butyl-c-2-ethenyl-r-1-cyclohexanol was unreactive owing to the steric interaction between the axial OH group and the axial H atoms at the 3- and 5-positions. In the cis-isomer the OH group occupies an equatorial position to bind to the lipase, and less bulky axial alkenyl and alkynyl groups might not so much prevent acetylations than an alkyl group.
Regioselective SN2 opening of α,β-ethylenic epoxides by RLi-BF3 combination
Alexakis, Alexandre,Vrancken, Emmanuel,Mangeney, Pierre,Chemla, Fabrice
, p. 3352 - 3353 (2007/10/03)
Organolithium reagents effect a regioselective SN2 nucleophilic cleavage of α,β-ethylenic epoxides only when BF3·Et2O is added. The reaction works with a variety of RLi reagents and with cyclic as well as acyclic epoxides. The Royal Society of Chemistry 2000.
BORON FLUORIDE PROMOTED OPENING OF EPOXIDES BY ORGANOCOPPER AND CUPRATE REAGENTS
Alexakis, A.,Jachiet, D.,Normant, J. F.
, p. 5607 - 5620 (2007/10/02)
In the presence of BF3 the reaction rate of organocopper and cuprate reagents with poorly reactive epoxides is dramatically enhanced.Lithium organocuprates are the best choice among the various organocopper and cuprate reagents tested.Even the dimesityl cyanocuprate is able to react with cyclohexene oxide in excellent yield.No products of cationic rearrangements are observed.The reaction with various epoxides shows a complete stereochemical (pure anti opening) and regiochemical control (attack on the less hindered side of the epoxide).
EFFECTS OF LEWIS ACIDS ON HIGHER ORDER, MIXED CUPRATE COUPLINGS
Lipshutz, Bruce H.,Parker, David A.,Kozlowski, Joseph A.,Nguyen, Sam L.
, p. 5959 - 5962 (2007/10/02)
The presence of BF3*Et2O in reactions of R2Cu(CN)Li2 and RT(2-thienyl)Cu(CN)Li2 with epoxides and α,β-unsaturated ketones leads to dramatic enhancements in reaction rates and/or product yields relative to those observed in the absence of this L
THE ATE COMPLEXES OF ALUMINIUM. REACTIVITY AND STEREOSELECTIVITY WITH RESPECT TO EPOXIDES AND CARBONYL COMPOUNDS. CATALYTIC ACTIVATION BY SALTS OF TRANSITION METALS
Boireau, G.,Abenhaim, D.,Henry-Basch, E.
, p. 3061 - 3070 (2007/10/02)
When used in non-coordinating solvents (hydrocarbons) NaAlEt4 and LiAlnBu4 are good alkylation agents for epoxides.The presence of catalytic quantities of transition-metal salts, particularly NiCl2 or NiBr2, greatly accelerate the reactions, making them possible within a reasonable time in the case of disubstituted epoxides such as cyclohexene oxide, 2-3 epoxybutane, 1 phenyl-2,3-epoxybutane.In the case of aliphatic epoxides, dialkylmagnesium, NaAlEt4 and LiAlnBu4 lead mainly to alkylation of the least substituted carbon of the epoxide ring; while in the case of epoxides with C-O bond in the benzyl position, it is this carbon that is alkylated.The reaction always proceeds by total inversion of the configuration of the carbon in the epoxide ring, namely the site of the alkylation. NaAlEt4 is also good agent for alkylating carbonyl compounds when used in solvents of low basicity such as diethylether, or in totally non-coordinating solvents such as the hydrocarbons.The yields of the alcohol are greatly improved by using catalytic quantities of NiCl2.The behaviour of NaAlEt4 with 2-phenylpropanol is quite remarkable: in diethylether NaAl-Et4 gives predominantly the pair of enantiomers predicted by Cram's rule and with greater stereoselectivity than if EtMgBr was used, while in pentane the reaction is no longer stereoselective.Finally, with a cyclic ketone, 4-t-butylcyclohexanone, NaAlEt4 in diethylether and in hexane in the presence of NiCl2 gives predominantly the equatorial alcohol resulting from an axial attack, which is generally not favoured at all.
Kinetics and Activation Parameters for the Reduction of Alkylcyclohexanones by Lithium Tri-tert-butoxyaluminohydride
Wigfield, Donald C.,Gowland, Frederick W.
, p. 653 - 658 (2007/10/02)
The kinetics of reduction of 15 cyclohexanones by lithium tri-tert-butoxyaluminohydride in tetrahydrofuran solvent are reported.The data confirm that the reaction is well represented by a simple second-order kinetic process.Second-order rate constants determined at various temperatures are recorded and the activation parameters determined.Rate constants vary from 5.0E-3 to 4.4 l mol-1 s-1; these rate constants exceed those of reduction by NaBH4 by factors varying from 50 (unhindered cyclohexanones) to 450 (hindered cyclohexanones).The reductions appear to be nearly isoenthalpic, all but three of the values of ΔH(excit.) being in the range 6.8 +/- 0.8 kcal mol-1.Variations in rates between ketones are caused by changes in ΔS(excit.), and entropy is also more significant than enthalpy in the free-energy barrier to reaction.Mechanistic aspects of the reduction are discussed.
