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m�k���N�� Glycinea, A Novel Reducing System for Acetal Cleavage: BH3•S(CH3)2BF3•O(C2H5)2 Combination, Kinetics and Mechanism of the Reactions of Amine Boranes with Carbenium Ions, A comparative study of some molecular addition compounds of group IIIB elements. /Type /Metadata 5 Howick Place | London | SW1P 1WG.

/CropBox [0 0 595.276 841.89] Benzylidene acetals are widely used for the protection of 1,2- and 1,3-diols;[7] deprotection occurs readily under cata-lytic hydrogenation conditions or by hydrolysis.

PDFlib PLOP 2.0.0p6 (SunOS)/Acrobat Distiller 8.0.0 (Windows) >> The main advantage of benzylidene acetal is the ability for regioselective openings. Part I. thank DST (Unit on Nano Science and Technology) and CSIR, New Delhi, for research fellowships. Further investigation of the rate-limiting step of the reaction revealed a negative entropy of activation (ΔS⧧ = −9 cal mol−1 K−1) and an inverse solvent isotope effect (k(H2O)/k(D2O) = 0.62). >> /WPS-ARTICLEDOI (10.1002/anie.200905952) The mechanism of hydrolysis is consistent with the Michaelis−Menten kinetic model. 2013-10-03T16:29:49+05:30

/Parent 4 0 R

and A.B. Kinetic studies of borane and alane activation by Lewis acids.

The acidic reagent formed in situ from anhydrous AlCl(3) and H(2)O in 3:1 ratio is much more efficient for the reductive openings of the cyclic benzylidene acetals with Me(3)N x BH(3) in tetrahydrofurane than the AlCl(3) alone. /Type /Page

/Metadata 2 0 R /G12 14 0 R The results of the present study provide insights into the mechanisms of the hydroboration and reduction reactions. [Fc(BC(4)Ph(4))(2)] and the 4-Me-NC(5)H(4) adduct of monoborole [Fc(BC(4)Ph(4))], which led to quantitative transfer of the Lewis base. >> Thus, among such borane-amine addition compounds, the BH3-N-phenylamines emerge as unique hydroborating and reducing agents. Cu(OTf)2 is an efficient and dual-purpose catalyst for the highly regioselective reductive ring openings of benzylidene acetals with either BH3 or Me 2EtSiH to give the corresponding primary and secondary alcohols (see scheme).

USD 51.00 /Title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eductive openings of the dioxolane-type 3,4-O-benzylidene acetals of galactopyranoside are also very efficient and regioselective and give either 3-O-benzyl derivative (from 3,4-O-exo-benzylidene acetal) or 4-O-benzyl derivative (from 3,4-O-endo-benzylidene acetal) depending on the configuration of the acetal carbon atom. The latter condition was observed to be compatible with a variety of acid-sensitive functional groups, including allyl and enol ethers. 118 0 R 119 0 R 120 0 R 121 0 R 122 0 R 123 0 R 124 0 R]

%���� We thank DST and CSIR, India for financial support and DST-FIST for providing NMR facilities. 108 0 R 109 0 R 110 0 R 111 0 R 112 0 R 113 0 R 114 0 R 115 0 R 116 0 R 117 0 R

Under proposed conditions, the dioxane-type 4,6-O-bezylidene acetals of hexopyranosides give regioselectively the corresponding 4-hydroxy,6-O-benzyl derivatives in excellent yields. We thank V. Ram[emsp14]Kumar for single-crystal X-ray analysis. additional organizing element in these complexes. /Rotate 0 /Annots [22 0 R 23 0 R 24 0 R 25 0 R 26 0 R 27 0 R 28 0 R 29 0 R 30 0 R 31 0 R

/ProcSet [/PDF /Text /ImageB /ImageC /ImageI] >> >>

/Kids [7 0 R 8 0 R 9 0 R 10 0 R 11 0 R] <<

thank DST (Unit on Nano Science and Technology) and CSIR, New Delhi, for research fellowships. 15 0 obj We use cookies to improve your website experience. However, this does not account for the effect of acids on hydrolytic behavior. catalyzed by chiral Lewis acids. /ca 1 The reaction kinetics for a number of reductive openings of methyl 2,3-di-O-benzyl-4,6-O-benzylidene-alpha-D-glucopyranoside have been investigated. General Glycosylation Mechanism. /Resources << We analyzed the concentration and temperature dependence of the equilibria and estimated equilibrium constants and activation energies.

24 hours to view or download: Article Purchase �+Sl�V����˗���Gޗ"���%{O���ȇ�,Ej籬s�/�rF �}S��t���6�Z����;[�� Finally, our efforts to further enhance the borole ratio in ferrocenylboroles aiming at the synthesis of [Fc(BC(4)Ph(4))(4)] failed and, instead, generated an uncommon ansa-ferrocene containing two borole fragments in the 1,1'-positions and a B(2)C(4) ansa-bridge. In contrary, without activation, the regioselectivity is instead directed by the Lewis acid, as exemplified by the reaction with BH3 x THF. The regioselective ring opening of pyranosidic 4,6-p-methoxybenzylidene acetals with BH(3)/Bu(2)BOTf in THF can be tuned by adjusting the reaction temperature and reagent concentrations. 9 0 obj /MediaBox [0 0 595.276 841.89] effectively restricts rotation about the donor–acceptor bond between /Annots [98 0 R 99 0 R 100 0 R 101 0 R 102 0 R 103 0 R 104 0 R 105 0 R 106 0 R 107 0 R Note: All steps are in equilibrium and the reaction can proceed in either direction depending on the concentration of the individual constituents. This cleavage offers an attractive, alternate stereoselective route to stilbenes in a modified McMurry reaction.

Again, BH3-N-phenylamine complexes reduce cyclohexanone in THF at 25°C at reasonable rates, while others require acetic acid solvent or mineral or Lewis acids to achieve the desired reduction. Regioselectivity and Solvent Dependance, Acyclic stereoselection.

application/pdf The regioselectivity of borane reductions of cyclic acetals can be controlled by the choice of borane.

Reductive cleavage at 0 degrees C resulted in the exclusive formation of 4-O-p-methoxybenzyl (PMB) ethers, whereas reaction at -78 degrees C produced 6-O-PMB ethers in high yields. 2013-10-03T16:29:49+05:30 /Creator (3B2 Total Publishing System 7.51n/W) The one we predicted is called a hemiacetal.) /Rotate 0



The Stereochemistry of the Reduction of 4-t-Butylcyclohexanone with Trimethylamine Borane in the Presence and Absence of Boron Fluoride, Cleavage of sapogenin terminal rings with lithium aluminum hydride [1], A Rapid and Quantitative Exchange of The Boron Hydrogens in Trimethylamine Borane with D2O, Importance of the timing of bond breaking and bond making in acetal templates. 47 0 R 48 0 R 49 0 R 50 0 R]

Openings to give free HO-6 (using BH(3) x THF-AlCl(3)-THF or LiAlH(4)-AlCl(3)-Et(2)O) follow first order kinetics, while reactions yielding free HO-4 (using BH(3) x NMe(3)-AlCl(3)-THF or BH(3) x NMe(3)-BF(3) x OEt(2)-THF) follow higher order kinetics. /F5 19 0 R USD 350.00

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