Wet and Dry Processes for the Selective Transformation of Phosphonates to Phosphonic Acids Catalyzed by Brønsted Acids.

A "wet" process and two "dry" processes for converting phosphonate esters to phosphonic acids catalyzed by a Brønsted acid have been developed. Thus, in the presence of water, a range of alkyl-, alkenyl-, and aryl-substituted phosphonates can be generally hydrolyzed to the corresponding phosphonic acids in good yields catalyzed by trifluoromethyl sulfonic acid (TfOH) at 140 °C (the wet process). On the other hand, with specific substituents of the phosphonate esters, the conversion to the corresponding phosphonic acids can be achieved under milder conditions in the absence of water (the dry process). Thus, the conversion of dibenzyl phosphonates to the corresponding phosphonic acids took place smoothly at 80 °C in toluene or benzene in high yields. Moreover, selective conversion of benzyl phosphonates RP(O)(OR')(OBn) to the corresponding mono phosphonic acids RP(O)(OR')(OH) can also be achieved under the reaction conditions. The dealkylation via the generation of isobutene of di-tert-butyl phosphonate, and the related catalysis by TfOH took place even at room temperature to give the corresponding phosphonic acids in good to high yields. Nafion also shows high catalytic activity for these reactions. By using Nafion as the catalyst, phosphonic acids could be easily prepared on a large scale via a simple process.

Radical Hydrophosphorylation of Alkynes with R2P(O)H Generating Alkenylphosphine Oxides: Scope and Limitations.

Radical hydrophosphorylation of aliphatic terminal alkynes with H-phosphine oxides can produce the corresponding anti-Markovnikov alkenylphosphorus adducts in moderate yields. This method is a cleaner approach for the preparation of the corresponding alkenylphosphine oxides, since it avoids the use of a metal catalyst that sometimes is difficult to remove from the products.

Stereospecific halogenation of P(O)-H bonds with copper(II) chloride affording optically active Z1Z2P(O)Cl.

A general and efficient method for the preparation of optically active Z1Z2P(O)Cl from the easily prepared optically active H-phosphinates and H-phosphine oxides was reported. H-Phosphinates and H-phosphine oxides react stereospecifically with CuCl2 to produce the corresponding optically active Z1Z2P(O)Cl with retention of configuration at the phosphorus center. Optically active Z1Z2P(O)Cl reacts easily with a variety of nucleophiles to produce other chiral organophosphorus acid derivatives with inversion of configuration at phosphorus.

Iron-catalyzed cross coupling of P-H/C-O bonds: efficient synthesis of α-alkoxyphosphorus compounds.

An efficient P-C bond-formation through iron-catalyzed cross coupling of P-H/C-O bonds is developed for the first time. This reaction proceeds efficiently to produce the corresponding valuable α-alkoxyphosphorus compounds under mild conditions with a wide generality.