- Development of safe and economical synthesis of isoxazole
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Isoxazole is a five membered heterocyclic compound having various pharmacological actions. The new practical synthesis of isoxazole from the easily available malonadehyde tetraethyl acetal by avoiding the use of toxic reagent such as cadmium chloride under environment friendly conditions has been developed.
- Nitlikar, Lakshmikant H.,Shinde, Devanand B.
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p. 637 - 639
(2013/12/04)
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- Replacing conventional carbon nucleophiles with electrophiles: Nickel-catalyzed reductive alkylation of aryl bromides and chlorides
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A general method is presented for the synthesis of alkylated arenes by the chemoselective combination of two electrophilic carbons. Under the optimized conditions, a variety of aryl and vinyl bromides are reductively coupled with alkyl bromides in high yields. Under similar conditions, activated aryl chlorides can also be coupled with bromoalkanes. The protocols are highly functional-group tolerant (-OH, -NHTs, -OAc, -OTs, -OTf, -COMe, -NHBoc, -NHCbz, -CN, -SO2Me), and the reactions are assembled on the benchtop with no special precautions to exclude air or moisture. The reaction displays different chemoselectivity than conventional cross-coupling reactions, such as the Suzuki-Miyaura, Stille, and Hiyama-Denmark reactions. Substrates bearing both an electrophilic and nucleophilic carbon result in selective coupling at the electrophilic carbon (R-X) and no reaction at the nucleophilic carbon (R-[M]) for organoboron (-Bpin), organotin (-SnMe3), and organosilicon (-SiMe2OH) containing organic halides (X-R-[M]). A Hammett study showed a linear correlation of σ and σ(-) parameters with the relative rate of reaction of substituted aryl bromides with bromoalkanes. The small ρ values for these correlations (1.2-1.7) indicate that oxidative addition of the bromoarene is not the turnover-frequency determining step. The rate of reaction has a positive dependence on the concentration of alkyl bromide and catalyst, no dependence upon the amount of zinc (reducing agent), and an inverse dependence upon aryl halide concentration. These results and studies with an organic reductant (TDAE) argue against the intermediacy of organozinc reagents.
- Everson, Daniel A.,Jones, Brittany A.,Weix, Daniel J.
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supporting information; experimental part
p. 6146 - 6159
(2012/05/07)
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- Substituted diether diols by ring-opening of carbocyclic and stannylene acetals
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Reduction of malonaldehyde bis(ethylene and propylene acetals) with borane or monochloroborane produces diether diols 1 and 2 in high yield. Similar reduction of glyoxal his(ethylene acetals) has only limited utility for the preparation of tetrasubstituted triethylene glycols 3. Organotin chemistry is complementary: stannylene acetals prepared from disubstituted vicinal diols can be alkylated with half an equivalent of 1,2-dibromoethane to produce tetrasubstituted triethylene glycols 3, or with two equivalents of 2-chloroethanol to produce disubstituted triethylene glycols 4.
- Martinez-Bernhardt, Rolando,Castro, Peter P.,Godjoian, Gayane,Gutierrez, Carlos G.
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p. 8919 - 8932
(2007/10/03)
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- Synthesis of Malonaldehyde Monoacetals
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The synthesis of a series of malonaldehyde manoacetals is described.Selective hydrolysis or transacetalisation of 1,1,3,3-tetramethoxypropane and its analogues was proved to be a very general technique.
- Shi-Qi, Peng,Winterfeldt, Ekkehard
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p. 1045 - 1047
(2007/10/02)
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- A Convenient Synthesis of Substituted Polyether Diols
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Alkyl-substituted polyether diols (or polythioether diols), which are potential precursors to substituted crown ethers, are produced in high yield by the selective reductive cleavage of C-O bonds in bis(cyclic acetals) by borane or monochloroborane.
- Castro, Peter P.,Tihomirov, Serge,Gutierrez, Carlos G.
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p. 5179 - 5181
(2007/10/02)
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- SYNTHESIS AND SOME PROPERTIES OF CYCLIC ACETALS OF MALONALDEHYDE
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The Lewis acid-catalyzed addition of cyclic orthoformates to vinyl ethyl ether, which leads to the formation of malonaldehyde acetals, was studied.It is shown that of the linear-cyclic malonaldehyde acetals, 2-(2,2-diethoxyethyl)- and 5,5-dimethyl-2-(2,2-diethoxyethyl)-1,3-dioxanes are stable.The transacetalization of 1,1,3,3-tetraethoxypropane with 1,2- and 1,3-diols, which leads to the formation of cyclic malonaldehyde acetals, was studied.The physicochemical constants of the acetals were determined, and their 1H and 13C NMR spectra are described.
- Imashev, U. B.,Kalashnikov, S. M.,Gordeeva, G. N.
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p. 369 - 373
(2007/10/02)
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