On 1.2‐Shift Reactions and CH‐Insertions of Acyclic Alkylidene CarbenesTwo series of acyclic terminal vinyl bromides (1…4and5…7) were tested in the reaction with potassium tert‐butoxide as precursors of alkylidene carbenes. As expected1up to4only give 1‐alkynes whereas the 2‐methylated vinyl bromides5,6and7yield 1‐methylated cyclopentenes predominantly besides 2‐alkynes. The formation of cyclopentenes indicates a reaction route via alkylidene carbenes and 1,5‐CH‐insertion reactions, that of 2‐alkynes is convincing evidence for 1,2‐alkyl shift reactions in 2‐methyl substituted alkylidene carbenes. The selectivity of 1,5‐CH‐insertion depends on the degree of alkyl substitution of the C‐5‐atom. At 240