- Diazophosphonates: Effective Surrogates for Diazoalkanes in Pyrazole Synthesis
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Diazophosphonates, readily prepared from α-ketophosphonates by oxidation of the corresponding hydrazones in batch or in flow, are useful partners in 1,3-dipolar cycloaddition reactions to alkynes to give N-H pyrazoles, including the first intramolecular examples of such a process. The phosphoryl group imbues a number of desirable properties into the diazo 1,3-dipole. The electron-withdrawing nature of the phosphoryl stabilizes the diazo compound making it easier to handle, whilst the ability of the phosphoryl group to migrate readily in a [1,5]-sigmatropic rearrangement enables its transfer from C to N to aromatize the initial cycloadduct, and hence its facile removal from the final pyrazole product. Overall, the diazophosphonate acts as a surrogate for the much less stable diazoalkane in cycloadditions, with the phosphoryl group playing a vital, but traceless, role. The cycloaddition proceeds more readily with alkynes bearing electron-withdrawing groups, and is regiospecific with asymmetrical alkynes. The potential of diazophosphonates for use in bioorthogonal cycloadditions is demonstrated by their facile addition to strained alkynes.
- Green, Michael T.,Hayes, Christopher J.,Inman, Martyn,Lewis, William,Moody, Christopher J.,Nicolle, Simon M.,Ruffell, Katie,Smith, Frances R.
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p. 13703 - 13708
(2021/09/09)
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- Cycloadditions of cyclohexynes and cyclopentyne
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We report the strategic use of cyclohexyne and the more elusive intermediate, cyclopentyne, as a tool for the synthesis of new heterocyclic compounds. Experimental and computational studies of a 3-substituted cyclohexyne are also described. The observed regioselectivities are explained by the distortion/interaction model.
- Medina, Jose M.,McMahon, Travis C.,Jimnez-Oss, Gonzalo,Houk,Garg, Neil K.
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supporting information
p. 14706 - 14709
(2014/12/11)
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- Thermal rearrangements of 3,3-spiroalkylated pyrazoles: Ring expansion and novel cases of sequential 1,5-shifts
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A 3,3-spiro-(cyclopentyl)pyrazole containing electron withdrawing ester groups undergoes readily ring expansion in the form of the van Alphen-Huettel rearrangement. Subsequent post van Alphen-Huettel rearrangement involved a sequence of 1,5-shifts different from that suggested earlier. Reactive intermediates have been isolated and identified. The corresponding phenyl analog does not exhibit post van Alphen-Huettel rearrangement. A rationale for the different behavior is offered. X-Ray crystallography has been applied to differentiate between structurally similar product.
- Yen, Yao-Pin,Chen, Shih-Feng,Heng, Zan-Cheng,Huang, Jen-Chieh,Kao, Li-Chun,Lai, Ching-Cheng,Liu
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p. 1859 - 1871
(2007/10/03)
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- Convenient one-pot syntheses of pyrazoles from imines, a vilsmeier type reagent and hydrazine
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A simple one-pot procedure for the regioselective synthesis of pyrazoles from readily available starting materials is described. Vilsmeier type reagent 1 reacts with imines 10 (via the corresponding tautomeric secondary enamines) in tetrahydrofuran to give enaminoimine hydrochlorides 11. Nonsymmetrical imines generally react preferentially with 1 at the sterically less hindered α-position. The enaminoimine hydrochlorides 11 are transformed in situ to the corresponding pyrazoles 12 in moderate to high yields by the addition of hydrazine.
- Katritzky,Denisenko,Denisenko,Arend
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p. 1309 - 1314
(2007/10/03)
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- Intermediates for making N-aryl and N-heteroarylamide and urea derivatives as inhibitors of acyl coenzyme A: cholesterol acyl transferase (ACAT)
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Compounds of the formula STR1 wherein R21 and R22 are as defined in the specification which are intermediates useful in the preparation of compounds of the formula STR2 and the pharmaceutically acceptable salts thereof, wherein Q and R1 are as defined in the specification. The compounds of formula I are inhibitors of acyl coenzyme A: cholesterol acyltransferase (ACAT) and are useful as hypolipidemic and antiatherosclerosis agents.
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- New N-aryl and N-heteroarylamide and urea derivatives as inhibitors of acyl coenzyme A: cholesterol acyl transferase
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Compounds of the formula the pharmaceutically acceptable salts thereof, wherein Q and R1 are as defined below, and novel carboxylic acid and acid halide intermediates used in the synthesis of such compounds. The compounds of formula I are inhibitors of acyl coenzyme A: cholesterol acyltransferase (ACAT) and are useful as hypolipidemic and antiatherosclerosis agents.
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- Rearrangements of 1-Cyclohexenylmethylenes and Their Relevance to the Mechanism of the Phenylcarbene Rearrangement
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Gas-phase pyrolysis of 1-cyclohexenyldiazomethane (17) and (2-methyl-1-cyclohexenyl)diazomethane (36) leads to the generation of cyclohexenylmethylenes, 13 and 27, respectively, whose intramolecular rearrangement mechanism can be inferred from the stable end products.These substituted vinylmethylenes undergo intramolecular ?-addition, but apparently do not participate in all-carbon Wolff rearrangement.The relevance of these results to the mechanism of the phenylcarbene rearrangement is discussed, and it is suggested that a ?-route with a bicycloheptatriene-like transition state may operate.An attempt to generate 1,3-cyclohexadienylmethylene is described.
- Miller, Paula C.,Gaspar, Peter P.
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p. 5101 - 5107
(2007/10/02)
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- Cephem compounds having 3-bicyclic heterocyclic cation groups
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The invention relates to cephem compounds of high antimicrobial activity of the formula: STR1 wherein R1 is amino or protected amino, R2 is lower aliphatic hydrocarbon group, R3 is a group of the formula: STR2 wherein m is 0 and or 1, and n is 1 or 2, which may have a lower alkyl substituent at the N atom, and X is CH or N, and pharmaceutically acceptable salts thereof.
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