The reaction of secondary phosphines and di-1-adamantylphosphine oxide with trifluoroacetic anhydride and hexafluoroacetone

Article abstract of DOI:10.1016/0022-1139(95)03288-6

While the secondary phosphines (1-Ad)₂PH (1) (1-Ad=adamantyl) and Trt(Ph)PH (2) (Trt=triphenylmethyl) reacted readily with trifluoroacetic anhydride (TFAA) to give the trifluoroacetylphosphines 7 and 8. (1-Ad)₂P(:O)H (6) could not be converted into the corresponding trifluoroacetylphosphine oxide 10 by treatment with TFAA. Compound 10 was observed by ¹⁹F and ³¹P NMR spectroscopy in the reaction of (1-Ad)₂PC(:O)CF₃ (7) with (H₂N)₂C(:O)·H₂O₂. Two pathways were observed for the reaction of 1 with excess hexafluoroacetone (HFA), starting from the primary HFA adduct (1-Ad)₂PC(CF₃)₂OH (13). Oxidation of 13 led to the tertiary phosphine oxide 14 which was also available from (1-Ad)₂P(:O)H (6) and HFA. Isomerization of 13 gave (1-Ad)₂POCH(CF₃)₂ (15) whose oxidation with excess HFA furnished the phosphorane 16. Hydrolysis of 16 led to the phosphinic ester 17. As is known for Ph₂PH (3), Ph(C₆F₅)PH (4) reacted with HFA to give the α-hydroxyphosphine 19. No reaction was observed when Trt(Ph)PH (2) and (C₆F₅)₂PH (5) were treated with HFA.