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submitted on 16.07.2019 and posted on 16.07.2019by Jiajing Bao, Hailong Tian, Peicheng Yang, Jiachen Deng, Jinghan Gui
The development of new chemical transformations
to simplify the synthesis of valuable building blocks is a challenging task in
organic chemistry and has been the focus of considerable research effort. From
a synthetic perspective, it would be ideal if the natural reactivities of
feedstock chemicals could be diverted to the production of high value-added
compounds which are otherwise tedious to prepare. Here we report a chemical
transformation that enables facile and modular synthesis of synthetically
challenging yet biologically important functionalized butenolides from easily
accessible furans. Specifically, Diels–Alder reactions between furans and
singlet oxygen generate versatile hydroperoxide intermediates, which undergo
iron(II)-mediated radical fragmentation in the presence of Cu(OAc)2
or various radical trapping reagents to afford butenolides bearing a wide
variety of appended remote functional groups, including olefins, halides,
azides and aldehydes. The practical utility of this transformation is
demonstrated by easy diversification of the products by means of cross-coupling
reactions and, most importantly, by its ability to simplify the syntheses of
known building blocks of eight biologically active natural products.