Primary Phosphines and Phosphine Oxides with a Stereogenic Carbon Center Adjacent to the Phosphorus Atom: Synthesis and Anti-Markovnikov Radical Addition to Alkenes

Abstract

Organophosphorus compounds with stereogenic phosphorus and carbon atoms have received increasing attention. In this regards, primary phosphines with a stereogenic carbon atom adjacent to the phosphorus atom were synthesized by the reduction in phosphonates and phosphonoselenoates with a binaphthyl group. Their oxidized products, i.e., phosphine oxides with a stereogenic tetrasubstituted carbon atom, were found to undergo BEt3-mediated radical addition to cyclohexene to give P-stereogenic secondary phosphine oxides with a diastereoselectivity of 91:9. The products were characterized by ordinary analytical methods, such as Fourier transform infrared spectroscopy; 1H, 13C, and 31P NMR spectroscopies; and mass spectroscopy. Computational studies on the phosphorus-centered radical species and the obtained product implied that the thermodynamically stable radical and the adduct may be formed as a major diastereomer. The radical addition to a range of alkenes took place in an anti-Markovnikov fashion to give P-stereogenic secondary phosphine oxides. A variety of functional groups in the alkenes were tolerated under the reaction conditions to afford secondary phosphine oxides in moderate yields. Primary phosphines with an alkenyl group, which were generated in situ, underwent intramolecular cyclization to give five- and six-membered cyclic phosphines in high yields after protection by BH3.

Special Issue “Progress in Synthesis and Applications of Phosphorus-Containing Compounds”

“…A representative example for the utility of phosphorus-based ligands in asymmetric homogenous catalysis was reported by David Sémeril and Shaima Hkiri, who disclosed the synthesis of optically pure diphosphite in which the two phosphorus atoms were grafted on two proximally phenolic rings of calix [4]arene. The latter compound and two related calixarenyl diphosphites were employed as ligands in the rhodium-catalyzed asymmetric hydrogenation of α-dehydroamino esters, resulting in ee up to 95% being obtained.…”