Asymmetric hydrogenation - influence of the structure of carbohydrate derived catalysts on the relative enantioselectivity QH/Me regarding acid and ester substrates and its inversion - selectivity increase in water by amphiphiles
作者:Rüdiger Selke、Manuela Ohff、Andreas Riepe
DOI:10.1016/s0040-4020(96)00953-2
日期:1996.11
resulting in an unusual low relative enantioselectivityQ=qH/qMe of 0.3 for the precatalysts 4e and 4f. Deprotected, 4,6-OH-group bearing catalysts 1-4g,h generally show smaller differences of %ee in methanol or benzene, however, not in water. Under addition of amphiphiles a in comparison with blanks b the relative enantioselectivity Q=qa/qb clearly increases for both groups of catalysts - in most cases
4,6 - O-苄叉基保护的2,3-双(O-二苯基膦基)-δ-吡喃葡萄糖苷铑(I)螯合物预催化剂1-4e ,f显示了对(Z)-2- N-酰氨基丙烯酸甲酯的加氢作用6 -8随轴向取向的六吡喃糖苷取代基数量的增加,对映选择性逐步降低。对于类似的底物酸6h-8h的降低甚至更强,导致预催化剂4e和4f的相对低的相对对映选择性Q = q H / q Me为0.3。脱保护的含4,6-OH基的催化剂1-4g,h通常在甲醇或苯中显示出较小的%ee差异,而在水中则显示出较小的%ee差异。与空白b相比,在添加两亲性a的情况下,两组催化剂的相对对映选择性Q = q a / q b明显增加-在大多数情况下,Q值在3到8之间-与催化剂的中性或离子性质无关两亲的。