Ambiguous Reactivity of a Fluorinated Thiocarbonyl S-Imide; Unprecedented Rearrangement under FVP Conditions

Flash vacuum pyrolysis (FVP) of the N-(adamantan-1-yl)hexafluorothioacetone S-imide (1b) yielded an isomeric compound 4 without extrusion of the sulfur atom. On the other hand, thermolysis of the same S-imide in CDCl3-solution afforded dithiazolidine 5 as the main product. Thermal cleavage of 1b leading to in situ formation of hexafluorothioacetone is the primary reaction in solution. [3+2]-Cycloadditions of 1b with strained trans-cyclooctene and dimethyl norbornenedicarboxylate occurred smoothly at ambient temperature with no decomposition and/or isomerisation. Reactions with less reactive cycloaliphatic thioketones 8a-b were carried out at elevated temperature and gave products of multi-step processes. Isomerisation of 1b which competes with the cleavage to hexafluorothioacetone, is postulated in order to explain the structures of the isolated products.