Synthetic applications of the carbanion walk mechanism: A novel and facile method for the preparation of 1,3-dimethylenecyclobutane and conjugated vinylallene derivatives.

Treatment of allenyl sulfone 5 with one half equivalent of n-BuLi in refluxing THF affords a mixture of two dimers: 1,3-dimethylenecyclobutane 7 and vinylallene 6. At 0°C, only the second product is obtained. In contrast, treatment of the same sulfone (5) with a full equivalent of n-BuLi, followed by addition of α,γ,γ-trimethylallenyl phenyl sulfone results in the exclusive formation of 1,3-dimethylenecyclobutane 14, even at low temperatures.