NMR Spectroscopic Studies on the 1:1 Interaction of Tris(hydroxymethyl)phosphine with Cinnamic Acids

A 1:1 reaction of (HOCH 2 ) 3 P with the cinnamic acids ArCH=CHCO 2 H (Ar = Ph, o ‐ and p ‐C 6 H 4 OH) in acetone at 60 °C affords a phosphobetaine of the type (HOCH 2 ) 3 P + CH(Ar)CH 2 CO 2 – in 70–80 % yields; the products were characterized by 31 P{ 1 H}‐, 1 H‐, and 13 C{ 1 H}‐NMR spectroscopy, and mass spectrometry. In methanol, the compounds decompose partially to a tertiary phosphine of the type (HOCH 2 ) 2 PCH(Ar)CH 2 CO 2 H; the degree of decomposition decreases in the order Ar = o ‐C 6 H 4 OH > p ‐C 6 H 4 OH > C 6 H 5 . The 1:1 reaction of (HOCH 2 ) 3 P with cinnamic acid in CD 3 OD generates (DOCH 2 ) 3 P + CH(Ph)CH(D)CO 2 – and (DOCH 2 ) 2 PCH(Ph)CH(D)CO 2 D, whereby addition of a deuteron to the α‐C atom is stereospecific and leads to ( R , S )‐ and ( S , R )‐stereoisomers.