- A Facile Synthesis of Oxetane Derivatives for Preparing Cross-Linked Polyoxetane Resins Bearing the Bromide at the Spacer End
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3-(6-bromo-2-oxahexyl and 8-bromo-2-oxaoctyl)-3-methyloxetanes, and 1,8- and 1,10-bis(3-methyl-3-oxetanyl)-2,7-dioxaoctane and -2,9-dioxadecane were readily prepared in fairly good yields by the reaction of 3-hydroxymethyl-3-methyloxetane (1) with tetra-
- Motoi, Masatoshi,Suda, Hiroshi,Shimamura, Katsuhiko,Nagahara, Shinsuke,Takei, Mitsuru,Kanoh, Shigeyoshi
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- Highly Enantioselective, Hydrogen-Bond-Donor Catalyzed Additions to Oxetanes
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A precisely designed chiral squaramide derivative is shown to promote the highly enantioselective addition of trimethylsilyl bromide (TMSBr) to a broad variety of 3-substituted and 3,3-disubstituted oxetanes. The reaction provides direct and general access to synthetically valuable 1,3-bromohydrin building blocks from easily accessed achiral precursors. The products are readily elaborated both by nucleophilic substitution and through transition-metal-catalyzed cross-coupling reactions. The enantioselective catalytic oxetane ring opening was employed as part of a three-step, gram-scale synthesis of pretomanid, a recently approved medication for the treatment of multidrug-resistant tuberculosis. Heavy-atom kinetic isotope effect (KIE) studies are consistent with enantiodetermining delivery of bromide from the H-bond-donor (HBD) catalyst to the activated oxetane. While the nucleophilicity of the bromide ion is expected to be attenuated by association to the HBD, overall rate acceleration is achieved by enhancement of Lewis acidity of the TMSBr reagent through anion abstraction.
- Strassfeld, Daniel A.,Wickens, Zachary K.,Picazo, Elias,Jacobsen, Eric N.
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supporting information
p. 9175 - 9180
(2020/07/13)
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- Aliphatic polycarbonates produced from the coupling of carbon dioxide and oxetanes and their depolymerization via cyclic carbonate formation
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The (salen)CrCl/onium salt catalyzed coupling reactions of several oxetane derivatives and carbon dioxide are reported. The oxetanes investigated contain substituents in the 3-position covering a range of steric requirements. The oxetanes examined include, 3,3-dimethyloxetane, 3-methoxymethyl-3-methyloxetane, and 3-benzyloxymethyl-3-methyloxetane. The rates of reaction of these oxetanes with CO2 were found to be significantly slower than the corresponding process with the parent oxetane monomer. Furthermore, in these instances the formation of copolymer was found to proceed via the preformed cycloaddition product, i.e., the six-membered cyclic carbonate, to a greater extent and increasing with the steric bulk of the substituents on oxetane. For these sterically more hindered oxetanes, the CO2 coupling reaction carried out in toluene at 110 °C reached an equilibrium product distribution of copolymer to cyclic carbonate which increased in cyclic carbonate product with increasing steric requirements of the oxetane monomer. For example, the catalyzed coupling of the parent oxetane and CO2 provides a copolymer to cyclic carbonate ratio of greater than 95%, whereas the corresponding product distribution for 3-benzyloxymethyl-3-methyloxetane was observed to be 60%. The catalytic rate of depolymerization of a purified sample of the copolymer afforded from 3-benzyloxymethyl-3-methyloxetane and CO2 to the corresponding cyclic carbonate, 5-benzyloxymethyl-5-methyl-1,3-dioxan-2-one, was found to be greatly retarded when carried out in an atmosphere of CO 2.
- Darensbourg, Donald J.,Moncada, Adriana I.,Wei, Sheng-Hsuan
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experimental part
p. 2568 - 2576
(2012/03/26)
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- A ruthenium-catalyzed hydrosilane-induced polymerization of 3-alkyl-3-hydroxymethyloxetane derivatives: Facile access to functionalized polyoxetanes by virtue of organosilyl groups
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Ring-opening polymerization of 3-alkyl-3-alkoxymethyl- or 3-alkyl-3-siloxymethyloxetanes is catalyzed by a triruthenium cluster, [Ru 3{μ3-(η2,η3, η5-C12H8)}(CO)7], in the presence of trialkylsilanes, providing a novel accessible method for functionalized polyoxetanes of Mn = 103-105. Oxetanes having alkoxy-, fluoroalkoxy-, triethyleneglycoloxy-, and trialkylsiloxy functions undergo polymerization and copolymerization. Consumption rates of two monomers in the copolymerization of 3-benzyloxymethyl- and 3-trimethylsiloxymethyl-3-alkyloxetanes are almost the same, indicating formation of random copolymers. The organosilyl group in the polymer and copolymers with siloxymethyl side chains is converted to CH3OH or CH2OCOR groups by hydrolysis or silyl/acyl exchange. These protocols give the way to access polymers or copolymers bearing OH and OCOR side chains. A ruthenium-catalyzed reaction of 3-ethyl-3- hydroxymethyloxetane with trialkylsilanes results in dehydrogenative silylation to give 3-ethyl-3-siloxymethyloxetane, which is followed by ring-opening polymerization. Combination of tandem dehydrogenative silylation/ring-opening polymerization/the silyl/acyl exchange realizes one-pot synthesis of polymers with CH2OCOR side chains from 3-ethyl- 3-hydroxymethyloxetane. DSC analyses of the formed polymers provided Tg and Tm data, which are a good example showing that the polymer properties are controlled by appropriate selection of functional groups at the side chain.
- Harada, Nari-Aki,Yasuhara, Jushiro,Motoyama, Yukihiro,Fujimura, Osamu,Tsuji, Tetsuro,Takahashi, Takeshi,Takahashi, Yoshiaki,Nagashima, Hideo
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supporting information; experimental part
p. 26 - 39
(2011/03/22)
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