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 (RF=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.