Preparation and Reactivity of Mixed Benzylic 1, 1 -Dimetalloalkanes

The carbometalation of (α-styryl)magnesium or -lithium organometallics with various allylic zinc bromides allows a general preparation of mixed benzylic 1, 1-dimetalloalkanes in good to excellent yields. Their low reactivity can be increased by a transmetalation with copper cyanide leading to copper, zinc dimetallic reagents which are readily bis-allylated with allyl bromide or bis-stannylated with trimethyltin chloride. Transmetalation with 1 equiv of trimethyltin chloride in the absence of copper salts affords tin, zinc 1, 1-dimetallo derivatives that can be cleanly oxidized by air to aromatic ketones under very mild conditions (-10 to 0 °C, 0.5-4 h). The monolithiation of the bis(trimethylstannyl) derivative 7 provides the a-lithiated benzylic tin compound 8 whose reactivity is also described.