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Photochemical [2+2] Cycloaddition of Alkynyl Boronates
Oleksandr S Liashuk1,2,3, Oleksandr O Grygorenko1,3, Yulian M Volovenko1
1Chemical Faculty, Taras Shevchenko National University of Kyїv, Kyiv, Volodymyrska Street 60, 01601, Kyїv, Ukraine.
Abstract:
A photochemical [2+2] cycloaddition of alkynyl boronates and maleimides is reported. The developed protocol provided 35-70 % yield of maleimide-derived cyclobutenyl boronates and demonstrated wide compatibility with various functional groups. The synthetic utility of the prepared building blocks was demonstrated for a range of transformations, including Suzuki cross-coupling, catalytic or metal-hydride reduction, oxidation, and cycloaddition reactions. With aryl-substituted alkynyl boronates, the products of double [2+2] cycloaddition were obtained predominantly. Using the developed protocol, a cyclobutene-derived analogue of Thalidomide was prepared in one step. Mechanistic studies supported the participation of the triplet-excited state maleimides and ground state alkynyl boronates in the key step of the process.
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