Some rearrangements of unsaturated phosphonate esters: Triethyl phosphite/iodine as a reagent for dehydration and condensation.

A review is presented of the Claisen, Cope and Carroll rearrangements, with consideration of the mechanisms operative in and the synthetic applications of these reactions. The Claisen orthoester rearrangement of several systems derived from gamma,delta-unsaturated alpha-hydroxyphosphonates is described. The presence of the phosphoryl substituent appears to deactivate the Claisen system. A corresponding acetoacetic ester derivative failed to undergo a Carroll rearrangement. The [2,3] sigmatropic rearrangement of allylic sulphenates derived from gamma,delta-unsaturated alpha-hydroxyphosphonates is described. The rearrangement of Claisen systems generated by the addition of allylic alcohols to diethyl (3-methyl-buta-1,2-dienyl) phosphonate is reported. Where the participating alcohol is allyl alcohol the two possible ketonic products of Claisen rearrangement are formed at room temperature. The ready rearrangement observed in this case is explained in terms of the reaction proceeding via the first-formed allylic anion intermediates rather than via the neutral adducts. An example of a Cope rearrangement involving the participation of an allenic phosphonate ester is described., The product of this rearrangement, a mixture of isomeric dienes, was converted into the corresponding Diels Alder adduct upon reaction with N-phenyl maleimide. The synthesis of a vinylallenic phosphonate with the potential to undergo an intramolecular ene reaction was achieved. Although the product of the ene reaction, a l,3,5-hexatriene, was not isolated, species resulting from the cyclisation and aromatisation of this product were characterised. A modification to this system produced a vinylallenic phosphonate amenable to function as the diene fragment in a Diels Alder cycloaddition reaction. The formation of an adduct with N-phenyl maleimide is described. A short review of the use of PPh3/CCl4 as a reagent for dehydration and condensation is presented as an introduction to Part 2. The reaction between simple phosphites and elemental iodine is investigated and the use of the intermediate species formed as reagents for dehydration and condensation is described.