Phospha-Mannich reactions of phosphinous acids R₂P–OH and their derivatives

Secondary phosphine oxides R2P(O)H are a relatively stable tautomeric form of secondary phosphinous acids R2P–OH that with imine/iminium species, or their donors, compounds P(O)–Csp3–N linkage (the phospha-Mannich reaction). These can be referred to as (α-aminoalkyl)phosphine oxides, (α-phosphinoylalkyl)amines, P(O),N-acetals. Compared P–Csp3–N linkages P,N-acetals, products reactions involving phosphines R2PH, the is significantly more allows for many examples α-functionalized P(O),N-acetals and α-phosphinoylated N-heterocycles, whereas such P,N-acetals rare. Trivalent derivatives halides R2P–Hal, esters R2P–OR’ (phosphinites), amides R2P–NR’2 (aminophosphines), phosphides R2P–PR’2 (biphosphines) also participate in Mannich-type mechanisms depending on reactants. The react (α-alkoxyalkyl)amines (N,O-acetals) (α-haloalkyl)amines (N,Hal-acetals), respectively, via Arbuzov-type intermediates rearranged into alkyl (Arbuzov rearrangement). Furthermore, unlike phosphines, less sensitive oxidation, imines/iminium species generated not only under conventional Mannich conditions, i.e., from N,E-acetals (E = OH, O, N, halogen, etc.), but also, example, by oxidation α-C-atom amines, alcohols aldehydes than amines.