Allenylphosphonates with a 1,3,2-dioxaphosphorinane ring: Synthesis, structures, stability and utility

Synthesis, structures and stability (thermal and air) of allenylphosphonates of the type (OCH2CMe2CH2O)P(O)C(R)=C=CR′R″ and [R″R′C=C=C(R)P(O)(OCH2)2]2C are discussed. Thermally activated dimerization (cycloaddition) of (OCH2CMe2CH2O)P(O)C(H)=C=CMe2 leads to the phosphonocyclobutane [(OCH2CMe2CH2O)P(O)C(H)=]2[C-CMe2]2 (18). Many of these allenes undergo addition of diethylamine to lead to enaminophosphonates that are readily hydrolysed by water to lead to β-ketophosphonates. The latter compounds are useful as Horner-Wadsworth-Emmons (HWE) reagents. Molecular structures of (OCH2CMe2CH2O)P(O)C(CH2OH)=C=CH2 (6), [H2C=C=C(H)P(O)(OCH2)2]2C (9), (OCH2CMe2CH2O)P(O)CH=C=CH2 (12), [(OCH2CMe2CH2O)P(O)C(H)=]2[C-CMe2]2 (18), and the β-ketophosphonate (OCH2CMe2CH2O)P(O)CH2)-C(O)CHMe2 (24) have been determined. In compound 6, intermolecular hydrogen bonding between the phosphoryl oxygen and the hydroxyl group leading to an infinite chain is observed. In 6, there is a significant deviation (ca 7°) from the orthogonality expected between the planes containing 4 atoms of (a) H2C=C and (b) C=C(H)P in the allene part. In 9, weak C-H...O interaction between the phosphoryl oxygen atom and a CH2 proton of the six-membered ring is present.