Synthesis Based on Prototropic Rearrangement

When treated with potassium tcrt-butoxide, the [l-(prop-2-ynyl)alkyl]phosphonic diesters 370 (R = H, Me, Ph, etc.) undergo prototropic isomerization to the (1-R-buta-l, 3-dienyl)phosphonic diesters (371).  

An early report claimed that the treatment of diethyl prop-2-enylphosphonate with NaOEt brings about its isomerization to diethyl prop-l-enylphosphonate, which is followed by the addition of sodium diethyl phosphite (present in the Michaelis-Becker synthesis of the original substrate) to give tetraethyl (l,2-propanediyl)phosphonate. A later communication claimed that diethyl prop-2-enylphosphonate undergoes dimerization when treated with NaOEt the exothermic reaction was pictured as the addition of the substrate to diethyl prop-l-enylphosphonate (which itself does not dimerize) produced by rearrangement. Finally, the initial adduct (372) itself rearranges to 373  

Phosphorylation with (Et0)2P(0)Cl of the mesomeric anion obtained from diethyl prop-2-enylphosphonate and LiN(SiMe3)2, leads to the bisphosphonic derivative 338 (R = 

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