Several original allene syntheses are reviewed. Two novel organometallic approaches are discussed in some detail. Recent observations made in the case of the one‐step synthesis of allenes by homologation of alkynes are described. The reaction mechanism which is proposed is supported by X‐ray crystallographic data on a CuBr complex which appears to be a reaction intermediate.

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Several original allene syntheses are reviewed.

The title ylides (III), prepared by alkylation of (I), possess a non‐planar structure with the thiazine moiety adopting a boat‐like conformation, as evidenced by X‐ray studies of (IIIc) and (IIIf) (both P21/n, Z=4).

ChemInform Abstract (IIIa) (space group P212121 with Z=4).