Manganese‐Catalyzed and Promoted Reactions of H‐Phosphinate Esters

Abstract

H-Phosphinates react with alkenes and alkynes using catalytic manganese(II) acetate. Under stoichiometric conditions with manganeseA C H T U N G T R E N N U N G (III) acetate or with catalytic manganese(II) acetate + excess manganese(II) oxide various reactions like arylation or cyclization through radical oxidative arylation can take place. Whereas the chemistry of manganese is already well developed for the functionalization of H-phosphonates, the present methodology provides an unprecedented access to functionalized phosphinates in acceptable to good yields.

Recent advances in sulfur- and phosphorous-centered radical reactions for the formation of S–C and P–C bonds

“…Han and Zhao reported that radical reactions of optically pure (R P )-alkylphenylphosphinates 385 in a stereospecific fashion (Scheme 163) 265. The Montchamp group employed alkyl phosphonyl radicals for hydroalkylsphonylation of alkenes.The radicals generated form the treatment of ethyl alkylphosphinates with Mn(OAc) 3 were reacted with the alkenes without solvent to form products 386 (Scheme 164) 266. …”

Manganese‐Mediated Homolytic Aromatic Substitution with Phosphinylidenes

“…Our initial reaction (Scheme , Intermolecular) employed OctP(O)(OCy)H as a standard model H ‐phosphinate ester, Mn(OAc) 3 (2 equiv), and benzene in large excess. The phosphinate product was obtained in 37% yield . While mediocre, this yield is not very different from Effenberger's 48% with (EtO) 2 P(O)H (2 equiv), AgNO 3 (20 mol %), Na 2 S 2 O 8 (5 equiv) and benzene (1 equiv) …”

“…The intramolecular version was examined for the synthesis of P ‐heterocycles (Scheme , Intramolecular) . As expected for a cyclization, the yields were moderate to good.…”

“…During our initial foray into H ‐phosphinate arylation, we conceived a novel system: catalytic Mn(II) with excess MnO 2 (Scheme ). This gave an essentially undistinguishable isolated yield from the Mn(OAc) 3 reaction.…”

“…Of course, one possible solution to the cost of Mn(OAc) 3 is to prepare it from KMnO 4 and Mn(OAc) 2 •4 H 2 O, or better yet, recycle it! Nonetheless, our system is more convenient and much less expensive.…”