Rhodium skewphos

A Comparison Between the Homogeneous and the Anchored Rhodium Skewphos... 

KP(C6H4-4-NMc2)2 reacts with the appropriate diol ditosylates yielding the chiral phosphines 77-79. These analogs of the well known Chiraphos, BDPP (Skewphos) and DIOP can be made water soluble by protonation or quatemization. Quatemization can be achieved with (CH3)30Bp4 with the phosphoms atoms protected by complexation to Rh(I) [76]. This method of quatemization was originally introduced [77] to prepare 81 in its rhodium complex. It is remarkable, that DIOP which is known to be acid sensitive survives all these manipulations. 

Mikami developed a highly enantioselective spiro cyclization of 1,6-enynes 37 with cyclic olefin catalyzed by cationic skewphos rhodium(I) complex. This is the first example of Rh(I)-mediated spiro-construction via an ene-type cyclization (Scheme 9.10) [19]. The ene cyclization provided two spiro isomers 38 and 39, and the selectivity was found to be dependent on the substitution and on the temperature of the reaction. Interestingly, the use of the less rigid chiral diphos-phane (5,S-skewphos) gave better results in term of enantioselectivity compared to atropisomeric diphosphanes, thereby demonstrating the interest of conformational flexibility of the active rhodium species. 

Mikami, K., Yusa, Y, Hatano, M., Wakabayashi, K., Aikawa, K. (2004). Highly enantioselective spiro cyclization of 1,6-enynes catalyzed by cationic skewphos rhodium(l) complex. Chemical Communications, 98-99. 

Mikami K, Yusa Y, Hatano M, Wakabayashi K, Aikawa K (2004) Enantioselective spiio ene-carbocyclization of 1,6-enynes catalyzed by tropos rhodium(I) complex with skewphos ligand. Tetrahedron 60 4475 1480... 

---