Recent Synthetic Applications of Catalyst-Free Photochemistry

Catalyst-free photochemistry provides numerous opportunities toward sustainable synthesis because catalyst separation can usually be avoided, which is consistent with green chemistry principles. Complementary to the well-reviewed photoredox chemistry, this review specifically summarizes the synthetic applications of photochemistry without external catalysts reported since 2000. The selected examples include both natural product synthesis and new methodology development. This review is arranged based on the type of chromophore. It is our hope that this review will inspire more synthetic chemists to embrace photochemistry into their research plans. 1 Introduction 2 Photochemistry of Olefins 2.1 [2+2] Cycloaddition of Enones and Olefins 2.2 Cycloaddition of Olefins without Carbonyl Groups 2.3 Z/E Isomerization 2.4 Cyclization 2.5 Others 3 Photochemistry of C=O 3.1 The Paternò–Büchi Reaction 3.2 The Yang Photoenolization 3.3 The Norrish Type I Reaction 3.4 The Norrish Type II Reaction 3.5 Others 4 Photochemistry of Nitrogen-Containing Functional Groups 5 Photochemistry of Halogen-Containing Compounds 6 Conclusion and Outlook