Register to receive personalised research and resources by email, An International Journal for Rapid Communication of Synthetic Organic Chemistry, Low-Valent Titanium Mediated Reductive Cleavage of Benzylidene Acetals: A Modified Mcmurry Reaction, Bio-Organic Division , Bhabha Atomic Research , Centre, Mumbai, 400 085, India, /doi/pdf/10.1080/00397919808004285?needAccess=true. /ML 4 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. The metal?oxygen bond in some addition compounds of aluminium and gallium trihalides with ethers, NEW SYNTHESES OF β-ALKOXY KETONES AND β-KETO ACETALS, Complexing and exchange of boron, aluminum, and gallium chlorides with some Lewis bases, THE RELATIVE EASE OF REDUCTIVE CLEAVAGE OF 1,3-DIOXOLANES AND 1,3-DIOXANES IN ETHER SOLUTION BY LiAlH4–AlCl3, THE INFLUENCE OF SUBSTITUENTS ON THE EASE AND DIRECTION OF RING OPENING IN THE LiAlH4–AlCl3 REDUCTIVE CLEAVAGE OF SUBSTITUTED 1,3-DIOXOLANES, Chemo-, stereo- and regioselective hydrogenolysis of carbohydrate benzylidene acetals. The mechanisms of regioselective reductive openings of acetals were investigated in several model systems by a combination of Hammett plots, kinetic experiments, density functional calculations, and (11)B NMR. reactions of α,β-unsaturated aldehydes with 1,3-dienes. << P.S.K. /Rotate 0 /BitsPerComponent 8 /CreationDate (D:20100105163037+01'00') The fluorescently labeled xyloside was tested for uptake, antiproliferative activity, and glycosaminoglycan priming in different cell lines. provides a simple and logical basis for understanding the mechanistic basis 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. 10.1002/(ISSN)1521-3773 11 0 obj for understanding preferred transition state assemblies. /BM /Normal 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. Note: All steps are in equilibrium and the reaction can proceed in either direction depending on the concentration of the individual constituents. Its application in the synthesis of 1,4-dideoxy-1,4-imino-L-xylitol is also highlighted. 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. 32 0 R 33 0 R 34 0 R 35 0 R] Regioselective Oxidative Cleavage of Benzylidene Acetals: Synthesis of [alpha]- and [beta]-Benzoyloxy Carboxylic Acids /PageLabels 3 0 R /Resources 127 0 R The presence of water does not interfere with reductive ring opening and may contribute toward in situ generation of H(+) as a catalyst for 6-O-PMB ether formation. 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. %���� /F6 20 0 R Amongst different acetals, benzylidene acetals which have two 0- benzyl bonds are attractive substrates for this study. Unlike common borane derivatives such as [FcBMe(2)], which only forms a 2:1 adduct, we also succeeded in the isolation of a 1:1 Lewis acid/base adduct, with one nitrogen donor of 4,4'-bipyridine remaining uncoordinated. /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 endobj /Type /XObject 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. /Subtype /XML Consequently, caution is urged in considering possible interpretation of the acid-enhanced reactions of amine-boranes. /CropBox [0 0 595.276 841.89] >> /Type /Catalog additional organizing element in these complexes. endobj BH3-amine complexes containing an N-phenyl group are hydrolyzed by neutral hydroxylic solvents, while others require a strong acid medium for the hydrolysis. %PDF-1.5 endobj /Contents 96 0 R design of new enantioselective catalysts as well as a mechanistic principle /ColorSpace /DeviceRGB Lewis acid activation of BH3 x NMe3 increases the reaction rate and renders the borane the most electrophilic species, which associates to the more electron-rich oxygen of the acetal. /Metadata 2 0 R polymerization, its potential as a Lewis acid catalyst for organic transformation is now much more extensive. A self-assembled supramolecular host catalyzes the hydrolysis of acetals in basic aqueous solution. �^#�O1X��|�b[}[��� ����u�+oc[˹�v����)��V^v�����h��sFJyk��t��K� �-�� ��)&mG��[��Z� JP 95 0 R] << /Parent 4 0 R Nucleophile dependence, Amine Boranes. /Filter /FlateDecode When we do the experiment to test our prediction, we find that yes, the product we have predicted is formed. The benzylic radicals formed as a result of cleavage should provide, after quenching, the deoxygenated productls.