- Highly chemoselective reduction of amides (primary, secondary, tertiary) to alcohols using SmI2/amine/H2O under mild conditions
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Highly chemoselective direct reduction of primary, secondary, and tertiary amides to alcohols using SmI2/amine/H2O is reported. The reaction proceeds with C-N bond cleavage in the carbinolamine intermediate, shows excellent functional group tolerance, and delivers the alcohol products in very high yields. The expected C-O cleavage products are not formed under the reaction conditions. The observed reactivity is opposite to the electrophilicity of polar carbonyl groups resulting from the nX → πC=O (X = O, N) conjugation. Mechanistic studies suggest that coordination of Sm to the carbonyl and then to Lewis basic nitrogen in the tetrahedral intermediate facilitate electron transfer and control the selectivity of the C-N/C-O cleavage. Notably, the method provides direct access to acyl-type radicals from unactivated amides under mild electron transfer conditions.
- Szostak, Michal,Spain, Malcolm,Eberhart, Andrew J.,Procter, David J.
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supporting information
p. 2268 - 2271
(2014/03/21)
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- Electron transfer reduction of carboxylic acids using SmI 2-H2O-Et3N
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The first general method for efficient electron transfer reduction of carboxylic acids has been developed. The protocol using SmI2 - H 2O - Et3N allows for reduction of a variety of carboxylic acids in excellent yields and provides an attractive alternative to processes mediated by reactive alkali metals, lithium aluminum hydride, and boron hydrides. Of broader significance, the method allows acyl radical equivalents to be generated from carboxylic acids under mild reaction conditions.
- Szostak, Michal,Spain, Malcolm,Procter, David J.
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supporting information; experimental part
p. 840 - 843
(2012/04/11)
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- Preparation of samarium(II) iodide: Quantitative evaluation of the effect of water, oxygen, and peroxide content, preparative methods, and the activation of samarium metal
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Samarium(II) iodide (SmI2) is one of the most important reducing agents in organic synthesis. Synthetic chemistry promoted by SmI2 depends on the efficient and reliable preparation of the reagent. Unfortunately, users can experience difficulties preparing the reagent, and this has prevented realization of the full synthetic potential of SmI2. To provide synthetic chemists with general and reliable methods for the preparation of SmI2, a systematic evaluation of the factors involved in its synthesis has been carried out. Our studies confirm that SmI2 is a user-friendly reagent. Factors such as water, oxygen, and peroxide content in THF have little influence on the synthesis of SmI2. In addition, the use of specialized glovebox equipment or Schlenk techniques is not required for the preparation of SmI2. However, our studies suggest that the quality of samarium metal is an important factor and that the use of low quality metal is the main cause of failed preparations of the reagent. Accordingly, we report a straightforward method for activation of "inactive" samarium metal and demonstrate the broad utility of this protocol through the electron transfer reductions of a range of substrates using SmI2 prepared from otherwise "inactive" metal. An investigation into the stability of SmI2 solutions and an evaluation of commercially available solutions of the reagent is also reported.
- Szostak, Michal,Spain, Malcolm,Procter, David J.
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supporting information; experimental part
p. 3049 - 3059
(2012/06/01)
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- Liquid crystalline esters and mixtures
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Compounds of the formula STR1 wherein X2 is a single covalent bond or --COO--; X1 is a single covalent bond, --COO--, --CH2 CH2 -- or when X2 is --COO--, X1 also can be p--C6 H4 --, p--C6 H4 --CH2 CH2 --, --CH2 CH2 --p--C6 H4, p--C6 H4 --COO-- or --COO--p--C6 H4 ; ring A is a benzene ring or trans-1,4-cyclohexylene; ring B is a benzene ring or when X2 is --COO-- and X1 is a single covalent bond, --COO-- or --CH2 CH2 --, ring B also can be trans-1,4-cyclohexylene; Z1, Z2 and Z3 individually are hydrogen or when positioned on a benzene ring which is not linked directly with a further ring via a single covalent bond, Z1, Z2 and Z3 also can be halogen, cyano or methyl; Y2 is cyano, nitro, 2,2-dicyanovinyl or when Y1 is hydrogen Y2 also can be 2,2-dicyano-1-methylvinyl; Y1 is halogen, cyano, C1 -C3 -alkyl or, when X1 includes a benzene ring or --COO-- or Y2 is nitro or at least one of Z1 and Z2 is other than hydrogen, Y1 also can be hydrogen; and R1 is C1 -C12 -alkyl or when positioned on a benzene ring R1 also can be C1 -C12 -alkoxy, their manufacture and use in liquid crystalline mixtures are described.
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- The Synthesis and Liquid-Crystal Transition Temperatures of Some Fluoro-Substituted Benzonitriles
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Various laterally fluoro-substituted benzonitriles have been prepared containing a trans-4-(n-alkyl)cyclohexane ring linked to the 4-position of the benzonitriles either through a methyleneoxy (-CH2O-) or an ethylene (-CH2CH2-) bridge.The bridging group links the benzonitrile and cyclohexane rings either directly or through an additional 1,4-bonded cyclohexane or benzene ring.The synthesis and liquid-crystal transition temperatures of these new compounds are described.In several cases the nematic-isotropic transition temperatures of F-substituted benzonitriles are found to be higher than those of the non-laterally substituted analogues.
- Kelly, Stephen M.,Schad, Hanspeter
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p. 1444 - 1452
(2007/10/02)
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- The Properties of Liquid Crystal Materials Incorporating the -CH2O- Inter-ring Linkage
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To establish more securely the influence of the -CH2O- inter-ring linkage upon the properties of mesogens of both high and low dielectric anisotropy, a range of ethers with the following general structure has been prepared and their properties examined. The thermal and electro-optic properties of the compounds are discussed, and comparisons made where possible with analogous materials incorporating the -CH2CH2- linkage.
- Carr, N.,Gray, G. W.
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- SYNTHESIS AND SOME PHYSICAL PROPERTIES OF 1-CYCLOHEXYL-2-(4 double prime -HALOBIPHENYL-4 prime -yl)ETHANES.
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A series of 1-(trans-4 prime -n-alkylcyclohexyl)-2-(4 double prime -halobiphenyl-4 prime -yl)ethanes, which show nematic phases, was prepared. Their transition temperatures, enthalpies and entropies were measured. Their bulk viscosities, birefringences and dielectric constants were determined by extrapolation. The bulk viscosity as a function of the third power of the van der Waals radius of the halogeno group, the birefringence as a function of the van der Waals radius of the halogeno group, and the dielectric constants as a function of the dipole moment of the halogeno group are discussed for the 1-(trans-4 prime -n-propylcyclohexyl)-2-(4 double prime -halobiphenyl-4 prime -yl)ethanes.
- Takatsu,Takeuchi,Sato
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p. 345 - 355
(2007/10/02)
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- 1-(TRANS-4 prime -N-ALKYLCYCLOHEXYL)-2-(4 double prime -CYANOPHENYL)ETHANES - A NEW SERIES OF STABLE NEMATOGENS OF POSITIVE DIELECTRIC ANISOTROPY.
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The synthesis and some important properties of the 1-(trans-4 prime -n-alkylcyclohexyl)-2-(4 double prime -cyanophenyl)ethanes - where n-alkyl equals C//1 to C//7 - are described.
- Carr,Gray,McDonnell
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