Deprotonation of Methylphosphine Boranes

From a-lithiated carbanions 72, formylated (73), carboxylated (74), silylated (75) and aminated (76) P-stereogenic phosphine boranes have been prepared without loss of optical purity. Some of them can be further functionalised to obtain other interesting compounds. Furthermore, oxidative coupling with Cu(II) salts affords C2 diphosphine boranes of the DiPAMP family (77) and 

The carbanion derived from ( S)-PAMP BH3 can be easily quenched at low temperature with DMF affording the formylated phosphine borane 73 in 85% yield. This compound, although rather unstable, when freshly prepared reacted smoothly with amines and subsequently sodium triacetoxyborohydride under microwave irradiation (pW) to afford the desired p-aminophosphine boranes 79 in 84-96% yields and in optically pure form. 

Lithiated 71 (Ar = o-An, u-Tol and 1-Naphth) reacted with carbon dioxide affording the phosphinocarboxylic acid boranes 74 in 55-60% yields. Their deprotection using TFA, with retention of conflguration, and coupling with (S)-(—)-2-(diphenylphosphino)methylpyrrolidine furnished amidodiphosphines 81 (48-51% yield). Finally, carbonyl reduction with borane (and concomitant N-and P-protection) followed by a deboronation step gave access to P,N ligands 82. 

Metallated phosphine boranes 71 were used for regioselective ring opening of propene and styrene oxides to yield phosphino alcohols 86, which were condensed with bisphenol phosphochloridite to yield compounds 87. 

---

Double deprotonation of methylphosphine borane and addition of 111 produced an equimolar mixture of phospholane boranes 112. They were separated by meticulous column chromatography, yielding 38% yield of (/ p)-112, which was oxidatively dimerised to afford 113 in 50% yield. Although (/ p,/ p)-113 can obviously be prepared from the other enantiomer of 111, it was prepared by different protocols (see Scheme 2.40 in this chapter and Chapter 5, Section 5.3.2). 

---