- Lewis acid- and/or Lewis base-catalyzed [3+2] cycloaddition reaction: synthesis of pyrazoles and pyrazolines
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A facile, InCl3 and/or DABCO mediated 1, 3-dipolar cycloaddition of ethyl diazoacetate (EDA) with various activated olefins under solvent-free conditions at ambient temperature to afford 3, 5-disubstituted pyrazolines and pyrazoles in moderate
- Krishna, Palakodety Radha,Sekhar, Empati Raja,Mongin, Florence
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scheme or table
p. 6768 - 6772
(2009/04/11)
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- Effective Methods for the Syntheses of 2-Pyrazolines and Pyrazoles from Diazocarbonyl Compounds
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Dipolar addition of diazocarbonyl compounds to α,β-unsaturated esters and nitriles in the presence of pyridine results in the production 2-pyrazolines in nearly quantitative yields.In one case, reaction of α-diazoacetophenone with acrylonitrile, Michael addition of the 2-pyrazoline to the conjugated olefin is observed, but this process is minimized by limiting the amount of pyridine employed. 5-Cyano-2-pyrazolines are converted to derivative pyrazoles through alkoxide promoted hydrogen cyanide elimination.With vinyl sulfone, α-diazoacetophenone undergoes sequential dipolar addition, Michael addition, and vinyl sulfite elimination under exceptionally mild conditions to form the derivative β-(1-pyrazolyl)ethyl vinyl sulfone in good yield.
- Doyle, Michael P.,Colsman, Mark R.,Dorow, Roberta L.
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p. 943 - 946
(2007/10/02)
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- Cyclopropanation of α,β-Unsaturated Carbonyl Compounds and Nitriles with Diazo Compounds. The nature of the Involvement of Transition-Metal Promoters
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In the presence of molybdenum hexacarbonyl or molybdenum(II) acetate, ethyl diazoacetate and α-diazoacetophenone react with α,β-unsaturated carbonyl compounds and nitriles to form derivative cyclopropane and vinyl CH insertion products.In the absence of these promoters or in the presence of catalytic amounts of pyridine, 2-pyrazolines are the major or sole reaction products.Kinetic investigations for reactions between ethyl diazoacetate and α,β-unsaturated esters and nitriles in the presence of Mo(CO)6, Mo2(OAc)4, or pyridine demonstrate the absence of any significant influence by these molybdenum promoters or pyridine on the rates and activation parameters for ethyl diazoacetate decomposition.Representative 1-pyrazolines have been synthesized and observed to undergo dinitrogen extrusion without apparent influence by molybdenum promoters.The composite results suggest that these molybdenum promoted reactions occur by dipolar cycloaddition of diazocarbonyl compounds to α,β-unsaturated systems and that the derivative 1-pyrazoline intermediates undergo dinitrogen extrusion to form the observed cyclopropane and vinyl CH insertion products.Molybdenum promoters function to inhibit competitive tautomerization of the initially formed cycloaddition products.The relative effectiveness of a broad selection of transition-metal compounds in directing reactions between ethyl diazoacetate and α,β-unsaturated esters and nitriles to cyclopropane products is described.The cycloaddition / dinitrogen extrusion pathway is presented as a viable mechanism for cyclopropanation of α,β-unsaturated systems by diazo compounds, even for reactions performed in the presence of traditional cyclopropanation catalysts.
- Doyle, Michael P.,Dorow, Roberta L.,Tamblyn, William H.
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p. 4059 - 4068
(2007/10/02)
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