Product of uncommon reaction of 1,1,1-trifluoro-4-phenylbut-3-yn-2-one with diphenyldiazomethane

Abstract

1,1,1-Trifluoro-4-phenylbut-3-yn-2-one reacts with diphenyldiazomethane at 20°С in ethyl ether to afford 4-(trifluoromethyl)-1,1,6,6-tetraphenyl-4,6-dihydro-1H-benz[5,6]oxepino[4,5-c]pyrazole. The process involves a stage of [3+2]-cycloaddition of the reagents, and the arising 3H-pyrazole subsequently enters in an uncommon [3+6]-cycloaddition with 1 more molecule of diphenyldiazomethane. Further the formed diadduct of the initial acetylene suffers a 1,5-hydride shift and undergoes fragmentation with a loss of a nitrogen molecule thus converting into the final product.