- Spiro[1,2]oxaphosphetanes of nonstabilized and semistabilized phosphorus ylide derivatives: Synthesis and kinetic and computational study of their thermolysis
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A series of tri- and tetrasubstituted spiro-oxaphosphetanes stabilized by ortho-benzamide (oBA) and N-methyl ortho-benzamide (MoBA) ligands have been synthesized by the reaction of Cα,Cortho-dilithiated phosphazenes with aldehydes and ketones. They include enantiopure products and the first example of an isolated oxaphosphetane having a phenyl substituent at C3 of the ring. Kinetic studies of their thermal decomposition showed that the process takes place irreversibly through a polar transition state (ρ = -0.22) under the influence of electronic, [1,2], [1,3] steric, and solvent effects, with C3/P-[1,2] interactions as the largest contribution to ΔG of olefination. Inversion of the phosphorus configuration through stereomutation has been observed in a number of cases. DFT calculations showed that oBA derivatives olefinated through the isolated (N, O)(Ph, C6H4, C) oxaphosphetanes (Channel A), whereas MoBA compounds decomposed faster via the isomer (C6H4, O)(C, N, Ph) formed by P-stereomutation involving a MB2 permutational mechanism (Channel B). The energy barrier of P-isomerization is lower than that of olefination. Fragmentation takes place in a concerted asynchronous reaction. The thermal stability of oxaphosphetanes is determined by strong C3/P-[1,2] interactions destabilizing the transition state of olefination. The effect of charge distribution and C3/C4-[1,2] and C4/P-[1,3] steric and solvent interactions on ΔG was also evaluated.
- López, Jesús García,Sansores Peraza, Pablo M.,Iglesias, María José,Roces, Laura,García-Granda, Santiago,Ortiz, Fernando López
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supporting information
p. 14570 - 14591
(2020/11/20)
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- Synthesis of Trisubstituted Alkenyl Boronic Esters from Alkenes Using the Boryl-Heck Reaction
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The direct borylation of disubstituted alkenes is reported. These conditions allow for the conversion of a variety 1,1- and 1,2-disubstituted alkenes to trisubstituted alkenyl boronic esters with outstanding yields and excellent E/Z selectivities. The utility of this reaction has been demonstrated with several downstream functionalization reactions, which allow access to diverse, stereodefined, functionalized olefins. Mechanistic studies are consistent with a boryl-Heck pathway.
- Reid, William B.,Watson, Donald A.
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supporting information
p. 6832 - 6835
(2018/10/24)
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- Regioselective radical cyclization initiated by the reaction of allylic hydroperoxides with iron(II) sulfate
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Treatment of 1-methyl-2-methylene-1-cyclohexyl hydroperoxide with a mixture of FeSO4/CuCl2 yielded 1-(1-chlorocyclohexyl)ethanone as the major product consistent with 6-endo-trig cyclization of the intermediate 5-acetylhex-5-enyl rad
- Masuyama, Araki,Sugawara, Tomohiro,Nojima, Masatomo,McCullough, Kevin J.
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p. 353 - 366
(2007/10/03)
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- A Practical and Efficient Method for the Synthesis of β-Lactones
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This paper describes a convenient one-step preparation of β-lactames based on the addition of thiol ester enolates to carbonyl compounds.Under the proper conditions the resulting aldolates undergo spontaneous cyclization to produce β-lactones in good to excellent yield.The new β-lactone synthesis provides access to 2-oxetanones with a variety of substituents and substitution patterns.In general, thiol ester enolates combine with carbonyl compounds to form the less sterically crowded β-lactone diasteromers, and in some cases the reaction proceeds with excellent stereoselectivity.In conjunction with the stereospecific decarboxylation of β-lactones, this chemistry also provides a very attractive approach to the synthesis of substituted alkenes.
- Danheiser, Rick L.,Nowick, James S.
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p. 1176 - 1185
(2007/10/02)
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- BF3·OEt2 promotes fast, mild, clean and regioselective dehydration of tertiary alcohols
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BF3·OEt2 in methylene chloride at 25°C for 2 hours or less is shown to be effective for easy conversion of tertiary alcohols into the corresponding thermodynamically most stable alkenes.
- Posner,Shulman-Roskes,Oh,Carry,Green,Clark,Dai,Anjeh
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p. 6489 - 6492
(2007/10/02)
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- Olefin Synthesis by Vanadium(V)-Induced Oxidative Decarboxylation-Deoxygenation of 3-Hydroxy Carboxylic Acids
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Oxidative decarboxylation of 3-hydroxy carboxylic acids can be effected with various V(V) complexes.This process likely yields an intermediate 1,4-metalla diradical. β-elimination from this intermediate gives olefin and regenerates V(V), likely as VO2Cl.Thus, although the overall process involves no net change in oxidation state for vanadium, the decarboxylation process is oxidatively induced.Intramolecular trapping of the intermediate yields glycolate and then C-C cleavage products, and skeletal rearrangement gives ketonic products.Qualitatively, rates for oxidative decarboxylation of the acids and the stereospecificity of formation of olefinic products depend on the electron-withdrawing ability of groups attached to vanadium.Methodology is described for the preparation of tri- and tetrasubstituted olefins in high yield from appropriate 3-hydroxy carboxylic acid precursors.
- Meier, Ingrid K.,Schwartz, Jeffrey
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p. 5619 - 5624
(2007/10/02)
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- Photochemical Dehydrogenation of Alkanes Catalyzed by trans-Carbonylchlorobis(trimethylphosphine)rhodium: Aspects of Selectivity and Mechanism
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The photochemical dehydrogenation of alkanes is catalyzed in solution by trans-Rh(PMe3)2(CO)Cl with high efficiency; quantum yields up to 0.10 and turnover numbers as high as 5000 are achieved with cyclooctane as substrate.The intramolecular regioselectivity of the reaction is investigated with methyl-, ethyl-, and isopropylcyclohexane.In competition experiments, cyclooctane is found to be 17 times as reactive as cyclohexane; under carbon monoxide atmosphere, the selectivity is enhanced to a factor of 130.A kinetic isotope effect, kH/kD=5.3, is found for thedehydrogenation of C6H12/C6D12.Both intra- and intermolecular selectivities are consistent with a pathway involving a reversible C-H oxidative addition followed by a β-hydrogen elimination. trans-Rh(PMe3)2(CO)Cl is demonstrated to be the only significant photoactive species in solution.The dehydrogenation reaction is quenched by carbon monoxide with Stern-Volmer kinetics.On the basis of these results, a mechanism is proposed in which the enrgy needed to drive these thermodynamically unfavorable dehydrogenations is obtained only from Rh-CO bond photolysis.
- Maguire, John A.,Boese, William T.,Goldman, Alan S.
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p. 7088 - 7093
(2007/10/02)
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- Cyclizations of ω-Allenyl Radicals
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Allenyl halides of structure (CH3)2C=C=CH(CH2)nX with n=3-6 have been prepared and reacted with n-Bu3SnH to generate the corresponding radicals for examination of the cyclization reactions of these reactive intermediates.The observed hydrocarbon products indicate that cyclization occurs for the n=3,4, and 5 radicals but not for the n=6 species.The n=3 radical isomerizes very efficiently by intramolecular addition to the sp carbon of the allene group.The n=5 intermediate reacts relatively slowly by attack at the near sp2 carbon.Both cyclization modes are observed for the n=4 species.The details of these radical cyclizations are discussed.
- Apparu, Marcel,Crandall, Jack K.
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p. 2125 - 2130
(2007/10/02)
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