A new class of 3′-sulfonyl BINAPHOS ligands:: Modulation of activity and selectivity in asymmetric palladium-catalysed hydrophosphorylation of styrene

Palladium-catalysed monophosphorylation of (R)-2,2'-bisperfluoroalkanesulfonates of BINOL (R-F =CF3 or C4F9) by a diaryl phosphinate [Ar2P(O)H] followed by phosphine oxide reduction (Cl3SiH) then lithium diisopropylamide-mediated anionic thia-Fries rearrangement furnishes enantiomerically-pure (R)-2'-diarylphosphino-2'-hydroxy-3'perfluoralkanesulfonyl-1,1'-binaphthalenes [(R)-8ab and (R)-8g-j], which can be further diversified by Grignard reagent (RMgX)-mediated CF3-displacement [->(R)-8c-f]. Coupling of (R)-8a-j with (S)1,1'-binaphthalene-2,2'-dioxychlorophosphine (S)-9 generates 3'-sulfonyl BINAPHOS ligands (R,S)-10a-j in good yields (43-82%). These new ligands are of utlility in the asymmetric hydrophosphonylation of styrene (1) by 4,4,5,5-tetramethyl-1,3,2-dioxaphospholane 2-oxide (2), for which a combination of the chiral ligands with either [Pd(Cp)(allyl)] or [Pd(allyl)(MeCN)(2)](+)/NaCH(CO2Me)(2) proves to be a convenient and active pre-catalyst system. A combination of an electron-rich phosphine moiety and an electron-deficient 3'-sulfone moiety provides the best enantioselectivity to date for this process, affording the branched 2-phenethenephosphonate, (-)-iso-3, in up to 74% ee with ligand (R,S)-10i, where Ar=p-anisyl and the 3'-SO2R group is triflone.