New ω-ketovinyl phosphonates: inexpensive synthesis, isomerization studies and route for functionalized 1,3-butadienes

A straightforward and inexpensive synthetic protocol to access new ω-ketovinyl phosphonates is established from the Lewis or Brønsted acid mediated reactions of α-hydroxy allylic phosphonates with aromatic 1,3-diketones. Predominantly, FeCl3 or FeCl3∙6H2O has been preferred as easily available, inexpensive and efficient Lewis acid under solvent-free conditions. With experimental and theoretical support, we have demonstrated that some of the substituted open chain 1,3-diketones may exist predominantly in the keto form. Mild base mediated isomerization reactions for ω-ketovinyl phosphonates were carried out to generate corresponding allylic phosphonates. Utility of one of the allylic phosphonates in Horner–Wadsworth–Emmons (HWE) reactions facilitated access to variety of densely substituted 1,3-butadienes attached with 1,3-diketone functionality at the terminal carbon.

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