Lemieux's extensive work on replacement reactions at the anomeric center helped to establish the fact that the O-2-protecting group of a donor exerts powerful control over stereoselectivity in glycoside coupling reactions. This manuscript shows that the O-2-protecting group of a donor also exerts powerful, indeed sometimes total, control over regioselectivity in glycosidation of diols. The latter acceptors also exhibit preferences over the donor, thereby providing evidence for the concept of reciprocal donor acceptor selectivity (RDAS). The latter concept is put to the test by simultaneously presenting an acceptor diol with equivalent amounts of two donors, in the hope of achieving double differential glycosidation leading to one-pot assembly of a trisaccharide. When the pair of donors did not conform to RDAS principles the reaction did not proceed beyond a dissacharide. However, when the pair was RDAS sanctioned, a single trisaccharide (out of four possibilities) was obtained.Key words: regiocontrolled glycosidation, armed and disarmed donors, di- and trioxolenium ions, oxocarbenium ion.
Lemieux在异构中心的替代反应方面的广泛研究有助于确立这样一个事实:供体的O-2保护基在糖苷偶联反应中对立体选择性具有强大的控制作用。本文表明,供体的O-2保护基对二醇的糖苷化反应的位置选择性也具有强大的、有时甚至是完全的控制作用。后一种受体对供体也表现出偏好,从而为相互供体受体选择性(RDAS)概念提供了证据。后一概念通过同时将一个受体二醇与等量的两个供体呈现,希望实现双重差异糖苷化,从而实现三糖的一锅法组装。当这对供体不符合RDAS原则时,反应无法超过二糖。然而,当这对供体符合RDAS原则时,获得了一个单一的三糖(四种可能性中的一种)。关键词:位置控制的糖苷化,武装和非武装供体,二和三氧杂环丙阳离子,羰基离子。