Myers allene synthesis

Upon warming, this product undergoes an elimination of arylsulfinic acid to give an unstable diazene as a reactive intermediate.

[3][1] (Note: The IUPAC defines a sigmatropic rearrangement as a pericyclic reaction involving both breaking and formation of a new σ bond in which the total number of π and σ bonds do not change,[4] whereas a retro-ene reaction involves the fragmentation of a molecule to a fragment with a double bond with allylic hydrogen (the 'ene') and a multiple-bonded species (the 'enophile') via a cyclic transition state.

Both the first step (Mitsunobu reaction) and third step (sigmatropic reaction) are stereospecific, so the chirality of the propargyl alcohol controls the chirality of the resulting allene.

[6] The use of ortho-nitrobenzenesulfonylhydrazine gives reactants and intermediates with appropriate relative stability to enable the whole process to be performed as a one-pot reaction, though the order in which the reagents are mixed is important.

[6] Mechanistic studies suggest that the diazene is formed as mixture of cis and trans isomers that easily interconvert, and that the cis is what reacts most readily to form the allene.