1 -Phenylphosphorinane-borane complex

The principle has been successfully applied to the differentiation between enantiotopic methylene groups in 1-phenylphospholane- and 1-phenylphosphorinane-borane complexes (199, 200) by Kobayashi and coworkers (equation 46) . The conditions for optimized yields, diastereomeric and enantiomeric ratios of appropriate 2-carboxylic acids 201 or 202 were carefully worked out. For the deprotonation of 199, the application of... 

Kobayashi and coworkers have demonstrated that optically active phos-pholane-2-carboxylic acid [n=l,Eq. (33)] and phosphorinane-2-carboxylic acid (n=2) can be prepared by asymmetric carboxylation of the phosphine-borane complexes. High trans selectivity and excellent enantiomeric excesses of the trans isomers were achieved on treatment of 1-phenylphospholane-borane and 1-phenylphosphorinane-borane complexes with s-BuLi-(-)-sparteine and subsequently with CO2. Notably, enantioselectivity was improved up to 92% ee when 1-phenylphospholane-borane was treated with s-BuLi-(-)-sparteine at 25°C, compared with 83% ee at -78°C [87]. 

---