2.4.6- Trifluoromethyl-2-methyl-27/-pyran

Cyclization. Constmction of ben2otrifluorides from aHphatic feedstocks represents a new technique with economic potential. For example, l,l,l-trichloro-2,2,2-trifluoroethane [354-58-5] and dimethyl itaconate [617-52-7] form 4-methoxy-6-trifluoromethyl-2JT-pyran-2-one [101640-70-4] which is converted to methyl 3-(trifluoromethyi)ben2oate [2557-13-3] ixh. acetjdene or norbomadiene (125). 

The palladium-catalyzed cyclization of ( )-3-alkynyl-3-trifluoromethyl allylic alcohols proceeds via a favourable 6-endo-dig cyclization due to the electron withdrawing properties of the trifluoromethyl group to afford 4-trifluoro-methyl-27/-pyrans (Equation 8) <2000TL7727>. 

With cyclic electron-deficient dienes, cycloaddition reactions are generally elTicient, in particular with electron-rich dienophiles. Methyl 2-oxo-6-(trifluoromethyl)-2/f-pyran-4-carboxylate (8) reacts with various alkenes to give cycloadducts. Only one regioisomer is obtained, in agreement with the prediction from orbital coefficients (Table 4). ... 

The most common method for the preparation of pyrazoles from other heterocycles is from pyranone-type compounds. Condensation of 2,3-dihydro /7-pyran -ones 787 with various aryl hydrazines in the presence of montmorillonite KSF clay under mild conditions proceeded rapidly to afford enantiomerically pure 5-substituted pyrazoles 788 (Equation 172) <2004TL6033>. Comparable results were obtained when arylhydrazines were reacted with 2-formyl glycals under microwave irradiation <2004TL8587>. Phenylhydrazine and hydrazine were reacted with 3-acetyl-4-hydroxy-6-methyl-2/7-pyran-2-one to afford 4-acetoacetyl-3-methylpyrazolin-5-ones, which were employed in the synthesis of bipyrazoles and pyrazoloisoxazoles <1999JHC1291>. Reaction of 3,3-dialkyl-6-(trifluoromethyl)-2,3-dihy-dro -pyrones with hydrazine hydrate afforded 3-(trifluoromethyl)-5-substituted-pyrazoles <1998RCB1365>. 

Pt-coordinated complexes of 2,4,6-trifluoromethyl-2-methyl-2//-pyran [80JCS(D)2095]. 

Methyl-2,2-bis(trifluoromethyl)-3,6-dihydro-2//-pyran (7) Typical Procedure 44... 

The AMI estimated activation barrier for nitrogen elimination was 17.5 kcal/mol. This means that isolation of the cycloadduct between cyclopropene and 2,5-bis(trifluoromethyl)-l,3,4-oxadiazole might be very hard. If we explore other cycloadducts between cyclopropene and 2 and 5 disubstituted 1,3,4-oxadiazoles and their activation barriers for nitrogen elimination, we can see that transition state structures are very similar with differences in C-N distance for the carbomethoxy substituent of 0.536 A, and the methyl substituent of 0.605 A instead of trifluoromethyl substitution. These results proved that all the transition state structures were very similar. That was also true for computed activation barriers. With carbomethoxy as a substituent, the activation barrier was 14.7 kcal/mol and with methyl as substituent, 16.7 kcal/mol. All of these values suggested that isolation of the cycloadduct might not be possible and that a substituted pyran should be expected as the final cycloaddition product. 

The butenolide, 3-(trifluoromethyl)-2//-furo[2,3-c]pyran-2-one, was obtained by treatment of 3-iodo-2//-furo[2,3-c]pyran-2-one with trifluromethyltriethylsilane in the presence of copper iodide and potassium fluoride in l-methyl-2-pyrrohdinone [45c]. 

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