Photoinduced Fragmentation Borylation of Cyclic Alcohols and Hemiacetals.
Photoinduced Fragmentation Borylation of Cyclic Alcohols and Hemiacetals.
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DOI：
10.1021/acs.orglett.0c02513
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发表时间：
2020-09
期刊：
影响因子：
5.2
通讯作者：
Chao Shu;R. Madhavachary;Adam Noble;V. Aggarwal
中科院分区：
文献类型：
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作者：
Chao Shu;R. Madhavachary;Adam Noble;V. Aggarwal
本文报道了邻苯二甲酰亚胺环烷醇与二（邻苯二酚）二硼的可见光光诱导断裂硼化反应。结构多样的酮基和甲酰氧基烷基硼酸酯被证明是方便地制备自由基介导的环醇和半缩醛，分别开环。该反应在温和的条件下进行，在没有添加剂或光催化剂，显示出优异的官能团耐受性，并显示出允许裂解的4-，5-，6-，和7-元环底物。该机制通过连续的均裂N-O和C-C键裂解进行，后者涉及烷氧基的β-断裂，产生羰基和被二硼试剂捕获的烷基。光谱研究表明，直接光激发的邻苯二甲酰亚胺或二硼基板与蓝光可以启动自由基链机制。
A visible-light photoinduced fragmentation borylation of O-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.