Influence of Configuration at the 4- and 6-Positions on the Conformation and Anomeric Reactivity and Selectivity of 7-Deoxyheptopyranosyl Donors: Discovery of a Highly Equatorially Selective <scp>l</scp>-<i>glycero</i>-<scp>d</scp>-<i>gluco</i>-Heptopyranosyl Donor
作者:Kapil Upadhyaya、Rahul S. Bagul、David Crich
DOI:10.1021/acs.joc.1c01535
日期:2021.9.3
of its side chain was the more equatorially selective isomer. In the d- and l-glycero-d-gluco glycosyl donors, the l-glycero-d-gluco isomer with the least disarming gauche,gauche side-chain conformation was the most equatorially selective donor. Variable temperature NMR studies, while supporting the formation of intermediate glycosyl triflates at −80 °C in all cases, were inconclusive owing to a change
四种过-O-苄基-d-或l-甘油-d-半乳糖和d-或l-甘油-d-葡萄糖庚基亚砜的制备及其侧链构象对糖基化反应反应性和立体选择性的影响是描述。这些供体的侧链构象由其与吡喃糖苷环的连接点和两个侧翼中心的相对构型决定,这与最近的模型一致。在d-和l-甘油中-d-半乳糖基供体,d-甘油-d-半乳糖异构体具有更多的吸电子反式,其侧链的左旋构象是更具赤道选择性的异构体。在d - 和l -甘油- d -葡萄糖糖基供体中,l -甘油- d -葡萄糖异构体具有最少的解除gauche,gauche侧链构象是最具赤道选择性的供体。变温 NMR 研究虽然支持在所有情况下在 -80 °C 下形成中间体糖基三氟甲磺酸酯,但由于分解机制随构型的变化而变化,因此尚无定论。有人提出,l-甘油-d-葡萄糖异构体的赤道选择性来自于糖基受体和供体的O6之间的H键,准备将受体反周面传递给三氟甲磺酸糖基,导致高度置换反应中的 S N