[2 + 2]‐Cycloaddition of a Vinyl Cation

The first cycloaddition to a vinyl catoin has now been accomplished: (2), obtained from (1) by solvolysis in the presence of AgBF4, reacts with cyclohexene to give mainly the cation (3) and thence to (4). In contrast, reaction with F3CCOOAg gives only the ester [(1), F3CCOO in place of Br]; the pronounced nucleophilic character of the trifluoroacetate ion prevents cycloadditon (An = p-methoxyphenyl).