Biaryl bisphosphine oxide

The apphcation of the rhodinm(l)-catalyzed double [2+2+2] cycloaddition approach to the synthesis of symmetric biaryl diphosphoms compounds was first accomplished in the reactions of l,4-bis(diphenylphosphinoyl)bnta-l,3-diyne with terminal diynes to give achiral biaryl bisphosphine oxides [23a]. Cj-Symmetric axially chiral biaryl diphosphonates were obtained with perfect enantioselectivity by using a phosphonate-substituted 1,3-bntadiyne and internal 1,6-diynes (Scheme 21.19) [23b]. Axially chiral biaryl dicarboxylates were also obtained by this method [23b]. 

The intramolecular [2+2+2] cycloaddition of triynes affords tricyclic compounds, which are not readily accessible by other methods. The double [2+2+2] cycloaddition of a diphenylphosphinoyl-substituted hexayne proceeded in the presence of the cationic rhodium(I)/tol-BINAP catalyst to give the corresponding Cj-symmetric axially chiral biaryl bisphosphine oxide with high enantioselectivity (Scheme 21.24) [28]. 

Use of the rhodium(I)-catalyzed double [2- -2-1-2] cycloaddition approach to the synthesis of symmetric biaryl diphosphorus compounds was first reported by Doherty et al. The reactions of l,4-bis(diphenylphosphinoyl)buta-l,3-diyne 81 with terminal a,co-diynes 80 proceeded at room temperature in the presence of the cationic rhodium(I)/BINAP catalyst to give symmetric biaryl bisphosphine oxides 82 in excellent yields (Scheme 9.29) [27]. Subsequent reduction of bisphosphine oxide 82 furnished the corresponding bisphosphine 83 (Scheme 9.29) [27]. 

Chan has discovered a completely atropdiasteroselective synthesis of a biaryl diphosphine by asymmetric intramolecular Ullmann coupling or Fe(m)-promoted oxidative coupling. A chiral atropisomeric biaryl bisphosphine ligand 2 was synthesized through this central-to-axial chirality transfer.38 Recently, a xylyl-biaryl bisphosphine ligand, Xyl-TetraPHEMP, was introduced by Moran, and is found to be effective for the Ru-catalyzed hydrogenation of aryl ketone.39... 

The cationic rhodium(l)/axially chiral biaryl bisphosphine complex-catalyzed [2+2+2] cycloaddition of biaryl-linked tetraynes with dialkynylketones or dialkynylphosphine oxides afforded helically chiral l,l -bitriphenylenes, containing adensely substituted fluorenone or phosphafluorene core (Scheme 21.23) [27]. 

Cationic rhodium(I)/chiral biaryl bisphosphine complexes are suitable for the enantioselective [2-I-2-1-2] cycloaddition reactions between electron-rich alkynes and electron-deficient unsaturated compounds (alkynes, nitriles, and isocyanates). Alkynylcarbonyl compounds, alkynylphosphonates, and alkynylphosphine oxides are the best-suited electron-deficient unsaturated compounds for these catalysts. These complexes are also able to catalyze the highly enantioselective synthesis of axially chiral anilides and bezamides. 

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