- Functional Polymers from (Vinyl)polystyrene. Recyclable Polymer-Supported Organosilicon Protecting Groups for Solid-Phase Synthesis
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Dicobalt octacarbonyl catalyzed the hydrosilylation of residual vinyl groups on insoluble porous beads of divinylbenzene-rich copolymer, exclusively with β orientation, by either dialkylhalosilanes or alkyldihalosilanes. The resulting silyl halide functionalities, now bound to a cross-linked polystyrene matrix through stable dimethylene spacers, could then be used to protect and immobilize hydroxyl-containing free molecules for their further modification in the course of solid-phase synthesis. The reaction proved selective for primary hydroxyls in the presence of secondary, and secondary over tertiary. Together with product free alcohols, later cleavage of these silyl ethers with aqueous acid or base also released the corresponding silanol groups, while HF, under particularly mild and selective conditions, left silyl fluorides that themselves could then be very conveniently regenerated by BCl3/CH2Cl2 back to the polymer-supported silyl chlorides. For a variety of possible applications, these solid-phase protecting groups offer control, yield, recovery, and reusability, as well as other possible advantages involving site-site isolation of functional groups within the cross-linked polystyrene matrix.
- Stranix, Brent R.,Liu, Hua Qin,Darling, Graham D.
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- Benzoxaborole Catalyst for Site-Selective Modification of Polyols
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The site-selective modification of polyols bearing several hydroxyl groups without the use of protecting groups remains a significant challenge in synthetic chemistry. To address this problem, novel benzoxaborole derivatives were designed as efficient catalysts for the highly site-selective and protecting-group-free modification of polyols. To identify the effective substituent groups enhancing the catalytic activity and selectivity, a series of benzoxaborole catalysts 1a–k were synthesized. In-depth analysis for the substituent effect revealed that 1i–k, bearing multiple electron-withdrawing fluoro- and trifluoromethyl groups, exhibited the greatest catalytic activity and selectivity. Moreover, 1i-catalyzed benzoylation, tosylation, benzylation, and glycosylation of various cis-1,2-diol derivatives proceeded with good yield and site-selective manner.
- Kusano, Shuhei,Miyamoto, Shoto,Matsuoka, Aki,Yamada, Yuji,Ishikawa, Ryuta,Hayashida, Osamu
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supporting information
p. 1598 - 1602
(2020/02/11)
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- Selective mono-acylation of 1,2- and 1,3-diols using (α,α- difluoroalkyl)amines
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In the reaction of N,N-diethyl-α,α-difluorobenzylamine (DFBA) with 1,2- or 1,3-diols, selective mono-benzoylation occurs to afford mono-esters of the diols in good yield. The reaction is completed under mild conditions in a short reaction time. Further, prim-, sec-, and tert-diols and catechol can be converted to the corresponding mono-benzoates. DFBA is used for the protection of the hydroxy group in sugars. The selective mono-nicotinylation, formylation and pivaloylation of diols are also performed by using the corresponding difluoroalkylamines.
- Wakita, Natsumi,Hara, Shoji
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experimental part
p. 7939 - 7945
(2010/10/19)
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- Oxidative transformation of 1,3-dioxacycloalkanes induced by chlorine dioxide
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The products and kinetic regularities of the reactions of 1,3-dioxacycloalkanes with chlorine dioxide were studied. The effects of the nature of solvent and the temperature on the reaction rate were considered and the activation parameters were determined.
- Abdrakhmanova,Kabal'nova,Rol'nik,Yagafarova,Shereshovets
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p. 1755 - 1760
(2007/10/03)
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- Transformations of cyclic acetals under the action of some organic and inorganic oxidants
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Liquid-phase oxidation of cyclic acetals and 2,2-disubstituted 1,3-dioxacyclanes with dimethyldioxirane, Caro salt, potassium persulfate, and complex of potassium chlorodiperoxochromate with 15-crown-5 was studied.
- Akbalina,Zlotskii,Kabal'nova,Grigor'ev,Kotlyar,Shereshovets
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p. 1120 - 1122
(2007/10/03)
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- Facile oxidative cleavage of benzylidene acetals using molecular oxygen catalyzed by N-hydroxyphthalimide/Co(OAc)2
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Benzylidene acetals derived from 1,2- and 1,3-diols undergo facile oxidative cleavage to give hydroxy benzoate esters with molecular oxygen in the presence of catalytic amount of N-hydroxyphthalimide/Co(OAc)2.
- Chen, Yongsheng,Wang, Peng George
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p. 4955 - 4958
(2007/10/03)
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- Chemo- and stereoselective monobenzoylation of 1,2-diols catalyzed by organotin compounds
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A new facile method for monoacylation of diols has been developed. A variety of cyclic and acyclic diols, in particular 1,2-diols, were selectively monobenzoylated in good yields by the reaction with benzoyl chloride in the presence of a catalytic amount of dimethyltin dichloride and inorganic bases such as potassium carbonate. Furthermore, the method was successfully applied to a kinetic resolution of racemic 1-phenyl-1,2- ethanediol using a chiral organotin catalyst. The ee was dependent on the kind of base, water as an additive, and the reaction temperature.
- Iwasaki, Fumiaki,Maki, Toshihide,Onomura, Osamu,Nakashima, Waka,Matsumura, Yoshihiro
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p. 996 - 1002
(2007/10/03)
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- 2-Phenyl(heteryl)-Substituted 1,3-Dioxanium Salts in the Reaction with Trimethylsilylethynylmagnesium Bromide
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A method for preparation of 2-α-furyl(α-thienyl)-4-methyl-1,3-dioxanium hexachloroantimonates, their hydrolysis and reaction with trimethylsilylethynylmagnesium bromide are described.
- Kosulina, T. P.,Ol'khovskaya, L. I.,Kul'nevich, V. G.,Karataeva, F. Kh.
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p. 1538 - 1541
(2007/10/03)
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- Organotin-Mediated Monoacylation of Diols with Reversed Chemoselectivity: A Convenient Synthetic Method
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The organotin-mediated monoesterification of unsymmetrical diols with reversed chemoselectivity has been explored to ascertain scope and limits of the method and to provide an easy and convenient synthetic procedure.The reaction has been performed on a set of substituted diols with some acylating agents usually employed as protecting groups.Two different procedures have been devised to obtain either the desired diol monoesters directly or the corresponding trialkylsilyl ethers as protected derivatives.The latter provides a convenient approach to the preparation of easily interconvertible diol monoesters.Also, the reaction has been optimized as a one-pot procedure, avoiding the isolation and purification of the stannylated intermediates.The reversed monoesterification method has been successfully applied to 1,2-, 1,3-, and 1,4-diols of primary-secondary, primary-tertiary, and secondary-tertiary types and to ether functions containing 1,2-diols.Within its limits, the described method represents the first direct one-pot monoesterification of diols at the most substituted site, allowing some remarkable achievements as (a) an almost regiospecific reversed monobenzoylation of some 1,2-diols, (b) the selective acylation of the tertiary hydroxyl of a primary-tertiary diol, and (c) a highly selective preparation of secondary pivalate of primary-secondary diols.
- Reginato, Gianna,Ricci, Alfredo,Roelens, Stefano,Scapecchi, Serena
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p. 5132 - 5139
(2007/10/02)
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- Palladium(II)-catalysed Oxidative Ring Cleavage of Cyclic Acetals with t-Butyl Hydroperoxide: Preparation of Monoesters of Diols
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Reaction of five- and six-membered cyclic acetals with tBuOOH in the presence of palladium(II) catalyst gives monoesters of diols in good yields.
- Hosokawa, Takahiro,Imada, Yasushi,Murahashi, Shun-Ichi
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p. 1245 - 1246
(2007/10/02)
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- DIALKYL ACYLPHOSPHONATES: A NEW ACYLATING AGENT OF ALCOHOLS
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Diethyl benzoylphosphonate (1) underwent facile benzoylation of alcohols in the presence of DBU.Reactions of diols containing primary and secondary hydroxyl groups with 1 gave predominantly monobenzoates in which primary hydroxyl groups were highly selectively benzoylated.Related acylations were also described.
- Sekine, Mitsuo,Kume, Akiko,Hata, Tsujiaki
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p. 3617 - 3620
(2007/10/02)
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