An unusual acetylene–allene rearrangement in iodomethylates of cotarnine acetylene derivatives

N-Methylation of cotarnine–phenol propargyl ethers conjugates with MeI affords the corresponding quaternary ammonium derivatives with retained acetylenic moiety. 3-Hydroxyalk-1-yn-1-yl analogues in the course of such iodomethylation undergo isomerization into allenic derivatives which are transformed into acetylenic ones upon dissolution in DMSO.