Gualandi Andrea, Mengozzi Luca, Giacoboni Jessica, Saulnier Steve, Ciardi Moira, Cozzi Pier Giorgio
Alma Mater Studiorum, Dipartimento di Chimica "G. Ciamician", University of Bologna, Bologna, Italy.
Chirality. 2014 Oct;26(10):607-13. doi: 10.1002/chir.22303. Epub 2014 Mar 17.
Recently, the direct substitution of allylic, benzylic, and tertiary alcohols has been achieved via SN 1-type reactions with catalytic amounts of Brønsted or Lewis acids. When a new stereogenic center is formed most of these transformations produce the desired product as a racemate, as these reactions proceed through carbenium ions. The arsenal of activation modes available in organocatalysis can be used to set up suitable reaction conditions in which chiral nucleophiles (enamine catalysis) or chiral electrophiles (iminium catalysis, chiral counterion catalysis) can easily be generated. Recently, we have used stabilized carbenium ions, directly available or obtained from the corresponding alcohols, in new organocatalytic stereoselective SN 1-type reactions. The commercially available carbenium ion benzodithiolylium tetrafluoroborate can be used for the straightforward organocatalytic stereoselective alkylation of aldehydes. In this account we will illustrate the application of this methodology in the total synthesis of natural products and the preparation of valuable starting materials.
最近，通过与催化量的布朗斯特酸或路易斯酸进行SN1型反应，实现了烯丙醇、苄醇和叔醇的直接取代。当形成一个新的立体中心时，这些转化大多会产生外消旋体形式的所需产物，因为这些反应是通过碳正离子进行的。有机催化中可用的活化模式可用于建立合适的反应条件，在此条件下可轻松生成手性亲核试剂（烯胺催化）或手性亲电试剂（亚胺离子催化、手性抗衡离子催化）。最近，我们在新的有机催化立体选择性SN1型反应中使用了直接可得或由相应醇类得到的稳定碳正离子。市售的碳正离子四氟硼酸苯并二硫鎓可用于醛的直接有机催化立体选择性烷基化。在本报告中，我们将说明该方法在天然产物全合成及有价值起始原料制备中的应用。
