Fluorine-containing Substituents into Five-Membered Heterocycles via Fluoro-substituted 1,3-Dipoles

Introduction of Fluorine-containing Substituents into Five-Membered Heterocycles via Fluoro-substituted 1,3-Dipoles 

Orb H3CO2C—C=C-C02CH3. HgCj—C=C-C4H5, H—CSC-CO2CH3, HjC02C-CH=CH-C0,CHj. HjC=CH-C02CHj. HjC=CH-C=N 

In the absence of trapping reagents, trifluoroacetonitrile oxide dimerizes to give a trifluoromethyl-substituted furoxan or a l,4-dioxa-2,5-diazine, depending on the identity of the 1,3-dipolar species. 

The [3 + 2] cycloadduct formed on treatment of tetrakis(trifluoromethyl)-Dewar-thiophene with trifluoromethyl diazomethane isomerizes to give an annulated 3-trifIuoromethyl-l//-2-pyrazoline in the presence of acids and bases. Sulfur can be removed from both compounds on reaction with triphenylphosphine (80JA6633). 

Photolytic (68CB302) or rhodium-catalyzed decomposition of alkyl 3,3,3-trifluoro-2-diazopropionates gives carbenes and carbene complexes, respectively, which exhibit an enormous synthetic potential. [3 + 2] cycloaddition reactions have been performed, e.g., with nitriles to give 4-trifluoromethyl-substituted oxazoles [90JOC3383 9IJFC(52)149] 

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