Dialkynylphosphine oxides

Tanaka and co-workers reported the desymmetrisation of symmetrical dialkynylphosphine oxides mediated by chiral rhodium catalysts (Scheme 6.44). 

Scheme 6.44 Rh-catalysed enantioselective desymmetrisation of dialkynylphosphine oxides.

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]. 

Cycloaddition of dialkynylphosphine oxides with 1,6-diynes afforded arylalkynylphosphine oxides in the presence of a cationic Rh(I) complex involving a modified binap ligand (Scheme 34). ... 

The cationic rhodium(I)/axially chiral biaryl diphosphine complex catalyzed the enantioselective desymmetrization of symmetric dialkynylphosphine oxides via rhodium-catalyzed [2- -2-1-2] cycloaddition with 1,6-diynes to give / -stereogenic alkynylphosphine oxides (Scheme 4.50) [53]. This method was also applied to... 

Not only dialkynyl ketones but also dialkynylphosphine oxides could be employed for this process. Enantioenriched [7]- and [9]helicene-like molecules, containing a densely substituted phosphafluorene core, were synthesized successfully by the inter-molecular double [2 -I- 2 -I- 2] cycloaddition of phenol- or naphthol-linked tetraynes with dialkynylphosphine oxides in the presence of the cationic rhodium(I)/(/ )-Hg-BINAP or (i )-tol-BINAP catalyst (Scheme 10.22) [21]. 

Another approach to implement [2+2+2] cycloaddition is for the design of P-stereogenetic sites [100, 110]. Reacting the symmetrical dialkynylphosphine oxide 2.167 with 1,6-diyne 2.156 in the presence of cationic rhodium complexes produces the products of mono-addition 2.168 in high yield and high enantioselectivity (86-99%, 85-96% ee) with an asymmetric phosphorus atom rather than axial chirality (Scheme 2.58). 

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