Shu Chao, Madhavachary Rudrakshula, Noble Adam, Aggarwal Varinder K
School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, U.K.
Org Lett. 2020 Sep 18;22(18):7213-7218. doi: 10.1021/acs.orglett.0c02513. Epub 2020 Sep 9.
A visible-light photoinduced fragmentation borylation of -phthalimido cycloalkanols with bis(catecholato)diboron is described. Structurally diverse keto and formyloxy alkyl boronic esters are shown to be conveniently prepared by radical-mediated ring opening of cyclic alcohols and hemiacetals, respectively. The reactions proceed under mild conditions in the absence of additives or photocatalysts, display excellent functional group tolerance, and are shown to allow cleavage of 4-, 5-, 6-, and 7-membered ring substrates. The mechanism proceeds via sequential homolytic N-O and C-C bond cleavages, the latter of which involves β-scission of an alkoxy radical, generating a carbonyl and an alkyl radical that is trapped by the diboron reagent. Spectroscopic studies suggest direct photoexcitation of either the phthalimide or diboron substrates with blue light can initiate a radical chain mechanism.
本文描述了一种用双（邻苯二酚）二硼对邻苯二甲酰亚胺基环烷醇进行可见光光诱导碎片化硼化反应。结果表明，通过自由基介导的环醇和半缩醛分别开环，可以方便地制备结构多样的酮基和甲酰氧基烷基硼酸酯。该反应在无添加剂或光催化剂的温和条件下进行，具有出色的官能团耐受性，并且可以实现4元、5元、6元及7元环底物的裂解。其反应机理是通过依次进行的均裂N-O和C-C键裂解，其中后者涉及烷氧基自由基的β-断裂，生成一个羰基和一个被二硼试剂捕获的烷基自由基。光谱研究表明，用蓝光直接光激发邻苯二甲酰亚胺或二硼底物均可引发自由基链式反应机理。
