Figure 1.
Fritsch-Buttenberg-Wiechell rearrangement. (X = halogen; M = electropositive metal; R1, R2 = aryl, alkyl, vinyl or alkynyl; 1a: 1-haloolefin; 1b: 1,1-dihaloolefin; 2: carbenoid intermediate; 3: carbene intermediate; 4: alkyne). Reaction of 1a requires a base whereas reaction of 1b requires a reducing agent such as BuLi.
