Add time:07/13/2019         Source:sciencedirect.com

The in situ generated highly electrophilic nitrile imines derived from trifluoroacetonitrile are efficiently trapped by monomeric mercaptoacetaldehyde at room temperature in THF solution. The initially formed 1:1 adducts undergo spontaneous cyclization leading to 6-membered 5,6-dihydro-1,3,4-thiadiazin-5-ols bearing the CF3 group at the C(2) atom in good yields. Subsequent oxidation of the latter products using C5H5N∙HCl∙CrO3 (PCC) led smoothly to the expected 1,3,4-thiadiazin-5-ones as final products. Alternatively, analogous 2-trifluoromethylated heterocycles were obtained via trapping of the same nitrile imines with α-mercaptocarboxylic acids followed by 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide methiodide (EDC methiodide) induced cyclisation of the initially formed 1:1 adducts. In general, efficiency of the second approach was lower and depended on the type of substituent attached to phenyl ring in the starting 1,3-dipole.

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