PolyBorylated Alkenes as Energy‐Transfer Reactive Groups: Access to Multi‐Borylated Cyclobutanes Combined with Hydrogen Atom Transfer Event

• Published in: Angewandte Chemie 2024-06, Vol.136 (25), p.n/a
• Main Authors: Hanania, Nicole, Eghbarieh, Nadim, Masarwa, Ahmad
• Format: Article
• Language: English
• Subjects: Alkenes; Cyclobutane; Deuterium; Hydrogen; Hydrogen atoms; Lactones; Oxidation; Reagents
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.202405898

While polyborylated alkenes are being recognized for their elevated status as highly valuable reagents in modern organic synthesis, allowing efficient access to a diverse array of transformations, including the formation of C−C and C‐heteroatom bonds, their potential as energy‐transfer reactive groups has remained unexplored. Yet, this potential holds the key to generating elusive polyborylated biradical species, which can be captured by olefins, thereby leading to the construction of new highly‐borylated scaffolds. Herein, we report a designed energy‐transfer strategy for photosensitized [2+2]‐cycloadditions of poly‐borylated alkenes with various olefins enabling the regioselective synthesis of diverse poly‐borylated cyclobutane motifs, including the 1,1‐di‐, 1,1,2‐tri‐, and 1,1,2,2‐tetra‐borylated cyclobutanes. In fact, these compounds belong to a family that presently lacks efficient synthetic pathways. Interestingly, when α‐methylstyrene was used, the reaction involves an interesting 1,5‐hydrogen atom transfer (HAT). Mechanistic deuterium‐labeling studies have provided insight into the outcome of 1,5‐hydrogen atom transfer process. In addition, the polyborylated cyclobutanes are then demonstrated to be useful in selective oxidation processes resulting in the formation of cyclobutanones and γ‐lactones. A site‐ and regioselective synthesis of polyborylated cyclobutanes by photochemical [2+2]‐cycloaddition is reported. The reaction is enabled by triplet energy transfer to the polyborylated alkenes and operates with a wide array of polyborylated alkenes, and olefins, allowing for the creation of polyborylated‐biradical intermediates. A side‐product resulting from a 1,5‐hydrogen‐atom‐transfer (HAT) via a photo‐ene‐type reaction was also obtained.