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In conclusion, our results suggest that the chemistry of 7 and 12 in solution is the chemistry of "carbene complexes"2s affording nearly exclusively 6, while in the "gas phase" the typical products of 5 become dominant.26 Carbenoid chemistry the alkyllithium way can be shifted toward chemistry expected from free carbenes with our new method. Thus, the geminal dibromides studied in the gas phase give higher yields of hydrocarbons-thought to stem from free carbenes-than in solution. In cases in which a tosylhydrazone cannot be synthesized, the decomposition of geminal dibromides may be an alternative to the Bamford-Stevens reaction. From the product ratios of vinylallene (3) and cyclopentadiene (15), A H and AM' of the competing cyclopropylidene-allene and carbene-carbene rearrangement 1 -2 can be determined. Acknowledgment.We gratefully acknowledge support of this work by the Deutsche Forschungsgemeinschaft. We thank K. Gomann for skillful experimental and technical assistance. (25) Hoeg, D. F.; Lusk, D. I.; Crumbliss, A. L. J. Am. Chem. SOC. 1965, 87, 4147. (26) Seebachs' I3C NMR experiments demonstrate that there is a smooth transition of carbenoids to carbenes: Seebach, D.; Siegel, H.; Miillen, K.; Hiltbrunner, K. Angew. Chem., Inr. Ed. Engl. 1979, 18, 844. Siegel, H.; Hiltbrunner, K.; Seebach, D. Ibid. 1979, 18, 845.

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