Visible-Light-Driven [2 + 2] Photocycloadditions between Benzophenone and C═C Bonds in Unsaturated Lipids

Abstract

The [2 + 2] photocycloaddition of alkenes and carbonyls is of fundamental interest and practical importance, as this process is extensively involved in oxetane-ring constructions. Although individual carbonyl group or alkene moiety has been utilized as photoactive species for oxetane formations upon ultraviolet photoexcitation, direct excitation of the entire noncovalent complex involving alkene and carbonyl substrates to achieve [2 + 2] photocycloadditions is rarely addressed. Herein, complexes with noncovalent interactions between benzophenone and CC bonds in unsaturated lipids have been successfully characterized, and for the first time a [2 + 2] cycloaddition leading to the formation of oxetanes has been identified under visible-light irradiation. The mechanism of this reaction is distinctly different from the well-studied Paternò–Büchi reaction. The entire complexes characterized as dimeric proton-bonded alkene and carbonyl substrates can be excited under visible light, leading to electron transfer from the alkene moiety in fatty acyls to the carbonyl group within the complex. These results provide new insight into utilizing noncovalent complexes for the synthesis of oxetanes in which the excitation wavelength becomes independent of each individual substrate.

A visible-light activated [2 + 2] cycloaddition reaction enables pinpointing carbon–carbon double bonds in lipids

“…17,[36][37][38] The mild visible-light activated reactions have great potential to overcome these limitations. 39,40 Very recently, Ouyang et al reported visible-lightdriven photocycloaddition between benzophenone and C]C bonds in unsaturated lipids, which provided new insight into utilizing noncovalent complexes for the synthesis of oxetanes. 40 But no such reaction has been demonstrated for the comprehensive location of C]C bonds in structural lipidomics.…”

Visible-Light-Enabled Paternò–Büchi Reaction via Triplet Energy Transfer for the Synthesis of Oxetanes

“…Importantly, two successful examples of these [2+2] cycloadditions relying on visible light irradiation have recently been reported by the groups of Dell'Amico and Ouyang. [8][9] Although an important advancement, these reactions are typically dependent on substrates such as benzophenones and dicarbonyls, which absorb light in the near-UV or visible light region. Consequently, this approach is inherently limited to starting materials that incorporate either of the required photophysical features (Fig.…”

Chemical derivatization: recent advances in mass spectrometry imaging

“…Tang 等 人 [92] [180] . 常用的 PB 反应试剂有丙酮 [117,181,182] 、2-乙酰吡啶 [183] 、苯乙酮 [114] 、二苯甲酮 [121] 等. 丙 酮为 MS 分析不饱和脂类的主要衍生化试剂, 其在紫 外光照射下与不饱和脂类 C=C 发生化学衍生化反应, [117] .…”