Organosilver formation

As for the cyclopropane rearrangement, the reaction probably involved the formation of a cationic silver cationic species followed by regioselective o-bond migration, leading preferentially to the more stable carbocation intermediate that is finally intramolecularly trapped by the organosilver species (Scheme 3.25).39... 

Taking into account this lack of stereoselectivity and equilibration between allenic stereoisomers, Benn proposed a mechanism in which silver ion facilitates the acyloxy shift on formation of n complex (or a bridged ionic silver intermediate).52 The thus-formed acetoxyallenes would remain coordinated to silver, allowing the formation of an organosilver allyl cation. Free rotation at this stage would provide both acetoxy-allene isomers after reversible loss of silver (Scheme 3.32). 

Organosilver species and silver salts thus exhibit a wide variety of behaviors, and further work will probably unravel new roles in organic chemistry, especially for the formation of C-C bonds. 

Silver(I), Cu(II) and Hg(II) have been employed in the dimerization of 1 and discussed elsewhere as has the role of the first of these in the addition of alkenes, alkynes, allenes and conjugated dienes to cyclopropabenzene. It is more than probable that product formation with Ag(I) is dictated by electrophilic addition of the metal and subsequent interaction of the organosilver benzylic cation with the hydrocarbon reagent to give ring-opened or ring-expanded products. 

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