Dipropargyl sulfone

In the case of carboxylic acids [33], ketones [47] or sulfones [49], it was possible to prove a further prototropic rearrangement of allenes 19 with R2 = H yielding the alkynes 20. In other examples, the prototropic isomerization of the triple bond leads to conjugated dienes directly thus the allene of type 19 could only be postulated as an intermediate [50]. Braverman et al. showed that the allenes generated by prototropic isomerization of dipropargylic sulfones or sulfoxides, for example 24, are unstable. They are transferred rapidly via diradical intermediates to polycycles such as 27 [51-53],... 

Cao, X., Yang, Y., Wang, X. A direct route to conjugated enediynes from dipropargylic sulfones by a modified one-flask Ramberg-Backlund reaction. J. Chem. Soc., Perkin Trans. 1 2002, 2485-2489. 

---