Minimally Competent<i>Lewis</i>Acid Catalysts: Indium(III) and Bismuth(III) Salts Produce Rhamnosides (=6-Deoxymannosides) in High Yield and Purity
作者:Clifford Coss、Tucker Carrocci、Raina M. Maier、Jeanne E. Pemberton、Robin Polt
DOI:10.1002/hlca.201200528
日期:2012.12
impurities in addition to the desired glycosides. Enantiomerically pure rhamnosides (R)‐1 and (S)‐1 (Fig.) were obtained from L‐rhamnose peracetate 5 and (±)‐benzyl 3‐hydroxydecanoate (9) via the diastereoisomeric rhamnosides 10 (Table 2; Scheme 3). The much weaker Lewis acids InBr3 and Bi(OTfl)3 produced purer products in high yield under a wider range of conditions (higher temperatures), and were effective
癸烷-1-醇(糖基化2),(±) -癸-2-醇(3),和(±)-3-羟基癸酸酯(4)与大号-鼠李糖过乙酸酯5以产生鼠李糖苷(= 6-deoxymannosides )研究了在路易斯酸BF 3· Et 2 O,Sc(OTf)3,InBr 3和Bi(OTf)3存在下的6、7和8(表1)。虽然强路易斯酸BF 3 ⋅Et 2 O和钪(OTF)3作为糖基化促进剂有效,必须过量使用;然而,糖基化需要仔细控制反应时间和温度,并且这些路易斯酸除所需糖苷外还产生杂质。对映体纯鼠李糖苷([R )- 1和(小号) - 1(图)从得到的大号-鼠李糖过乙酸酯5和(±) -苄基-3-羟基癸酸酯(9)经由非对映异构鼠李糖苷10(表2 ;方案3) 。弱得多的刘易斯InBr 3和Bi(OTfl)3酸可在更宽的条件范围(更高的温度)下高收率地生产出较纯的产品,即使在催化下使用,其也是有效的糖基化促进剂(<10%催化剂;表2)