New methodology for the [4+3] cycloaddition reactions: generation of oxyallyl cations from α,α′-diiodoketones under sonochemical or thermal conditions

A new methodology to perform [4+3] cycloaddition reactions of suitable dienes and 1,3-dimethyl-2-oxyallyl cations is presented. The reaction is carried out starting from commercially available dienes and easy-handling α,α′-diiodoketones, which are reduced by the Zn/Cu couple to generate the oxyallyl cation as intermediate. The reaction is carried out under mild thermal or sonochemical conditions at low temperatures (from 0 to −44°C) and for short reaction times (<15 min). This methodology represents a good alternative respect to the actual procedures based on other reducing agents or starting from more elaborate precursors of the oxyallyl cations.