1-alkynylphosphines cycloaddition

The bulky phosphine ligands were synthesized via [2 + 2 + 2] cycloaddition of diynes with 1-alkynylphosphine sulfides using the cationic rhodium(I)/BINAP catalyst followed by desulfurization (Scheme 4.44) [47]. 

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... 

As shown in Sections 9.4.1 and 9.4.2, electron-deficient and coordinating alkynyl carbonyl compounds showed high reactivity in cationic rhodium(I)/biaryl bispho-sphine complex-catalyzed enantioselective [2- -2-1-2] cycloaddition. Therefore, Tanaka et al. investigated the use of alkynylphosphonates or alkynylphosphine oxides instead of alkynyl carbonyl compounds for the practical synthesis of axially chiral biaryl phosphorus compounds. The enantioselective [2- -2-1-2] cycloadditon... 

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. 

A useful approach to the preparation of bulky arylphosphines is rhodium-catalyzed [2- -2- -2] cycloaddition of 1-alkynylphosphine sulfides to 1,6-diynes followed by removing sulfur, which leads to phosphines with bulky aromatic substituents [102, 103]. Condensation of sulfides 2.153 with diynes 2.152 in the presence of cationic rhodium catalyst and the (R)-binap ligand gives arylphosphine sulfides 2.154 in moderate to good yields (44-97%) (Scheme 2.53) [100, 102, 103]. 

Scheme 2.53 Rhodium-catalyzed formal [2-1-2- -2] cycloaddition reactions of 1-alkynylphosphine sulfides with tethered diynes.

A practical method for the synthesis of axially chiral biaryl monophosphine oxides was developed by Tanaka and coworkers [104]. Enantioselective [24-24-2] cycloaddition of 1-alkynylphosphine 2-naphthol derivatives 2.157 with 1,6-diyne 2.156 in the presence of cationic rhodium catalyst including (R)-H8-binap (i.e., (R)-(4-)-2,2 -bis(diphenylphosphino)-5,5, 6,6, 7,7, 8,8 -octahydro-l,l -binaphthyl) leads to axially chiral phosphine oxides 2.158 in high yields and high enantioselectivity (Scheme 2.54)... 

The syntheses of axially chiral biarylphosphine oxides based on alkynylphosphine oxide 2.157 and acetylene was carried out using chiral cobalt catalyst 2.159 [100, 105, 106]. The [24-24-2] cycloaddition, however, resulted in axially chiral biarylphosphine oxides 2.160 with moderate yield and enantioselectivity (Scheme 2.55). It was accompanied by a recovery of some of the corresponding phosphines. The newly obtained phosphines were used in the reaction of palladium-catalyzed hydrosilylation of unsymmetrical alkenes [100]. 

Scheme 2.58 Enantioselective synthesis of P-stereogenic alkynylphosphine oxides by rhodium-catalyzed [24-24-2] cycloaddition reactions.

Kondoh, A., Yorimitsu, H. and Oshima, K. (2007) Synthesis of bulky phosphines by rhodium-catalyzed formal [2-1-2- -2] cycloaddition reactions of tethered diynes with 1-alkynylphosphine sulfides. Journal of the American Chemical Society, 129(22), 6996-6997. 

Nishida, G., Noguchi, K., Hirano, M. and Tanaka, K. (2008) Enantioselective synthesis of P-stereogenic alkynylphosphine oxides by Rh-catalyzed [24-24-2] cycloaddition. Angewandte Chemie International Edition, 47(18), 3410-3413. 

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