3-P⩵O-Functionalized Phospholane 1-Oxides by the Michael Reaction of 1-Phenyl-2-phospholene 1-Oxide and Dialkyl Phosphites, H-Phosphinates, or Diphenylphosphine Oxide

The addition of dialkyl phosphites, H-phosphinates, and diphenylphosphine oxide on the β carbon atom of the not too reactive double bond of 1-phenyl-2-phospholene 1-oxide was carried out in two ways. According to the first approach (A), the P-reagents were activated by trimethylaluminum prior to the Michael addition. The second method (B) involved the microwave(MW)-assisted solventless reaction of the P-species with the phospholene oxide. In general, method A was more efficient and more selective than route B. However, the addition of dialkyl phosphites and diphenylphosphine oxide could also be accomplished well under MW conditions. The disadvantage of the MW-assisted approach is that the Michael adducts are formed as a mixture of isomers. The 3-P⩵O-phospholane oxides are novel products, and among these, the bis(phosphine oxide) is the precursor of the bidentate P-ligand LuPhos.