Photomechanochemical control over stereoselectivity in the [2 + 2] photodimerization of acenaphthylene

• Published in: Faraday discussions Vol. 241; p. 266
• Main Authors: Biswas, Sankarsan, Banerjee, Sayan, Shlain, Milan A, Bardin, Andrey A, Ulijn, Rein V, Nannenga, Brent L, Rappe, Andrew M, Braunschweig, Adam B
• Format: Journal Article
• Language: English
• Published: England 05-01-2023
• Subjects: Acenaphthenes; Cyclobutanes; Density Functional Theory; Dimerization
• ISSN: 1364-5498
• DOI: 10.1039/d2fd00122e

Tuning solubility and mechanical activation alters the stereoselectivity of the [2 + 2] photochemical cycloaddition of acenaphthylene. Photomechanochemical conditions produce the
cyclobutane, whereas the solid-state reaction in the absence of mechanical activation provides the
. When the photochemical dimerization occurs in a solubilizing organic solvent, there is no selectivity. Dimerization in H
O, in which acenaphthylene is insoluble, provides the
product. DFT calculations reveal that insoluble and solid-state reactions proceed
a covalently bonded excimer, which drives
selectivity. Alternatively, the noncovalently bound
conformer is more mechanosusceptible than the
, meaning it experiences greater destabilization, thereby producing the
product under photomechanochemical conditions. Cyclobutanes are important components of biologically active natural products and organic materials, and we demonstrate stereoselective methods for obtaining
or
cyclobutanes under mild conditions and without organic solvents. With this work, we validate photomechanochemistry as a viable new direction for the preparation of complex organic scaffolds.