Some rearrangements of unsaturated phosphonate esters

Abstract

α-Hydroxyalk-2-enylphosphonates undergo Claisen orthoester rearrangement on heating with orthoesters, and their arylsulphenates undergo [2,3]-sigmatropic rearrangement to give 3-arylsulphinylalk-1-enylphosphonates. The addition of allyloxide anion to the central carbon of the allene Me₂CCCHP(O)(OEt)₂ is followed by rapid Claisen rearrangement of the resulting allylic carbanion to give the two possible β-ketoalkylphosphonates. Allenic phosphonates of the general formula R¹R²CCH[CH₂]_nCR³CCHP(O)(OEt)₂ have been prepared: when R¹= R²= H, R³= Me, and n= 2, Cope rearrangement occurs to give isomeric dienes; when R¹,R²,R³= Me and n= 0, [1,5] hydride shift gives a triene which then cyclises to a cyclohexadiene; when R¹= Me, R²= H, R³= H or Me, and n= 0, the diene component can be used in Diels–Alder reactions.