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This Account summarizes efforts in our group toward synthesis of heterocycles in the past decade. Selected examples of transannulative heterocyclizations, intermediate construction of reactive compounds en route to these important motifs, and newer developments of a radical approach are outlined.

1 Introduction

2 Transannulative Heterocyclization

2.1 Rhodium-Catalyzed Transannulative Heterocyclization

2.2 Copper-Catalyzed Transannulative Heterocyclization

3 Synthesis of Heterocycles from Reactive Precursors

3.1 Synthesis of Heterocycles from Diazo Compounds

3.2 Synthesis of Heterocycles from Alkynones

4 Radical Heterocyclization

4.1 Light-Induced Radical Heterocyclization

4.2 Light-Free Radical Heterocyclization

7 Conclusion

Dual light-excited ketone/transition-metal catalysis is a rapidly developing field of photochemistry. It allows for versatile functionalizations of C–H or C–X bonds enabled by triplet ketone acting as a hydrogen-atom-abstracting agent, a single-electron acceptor, or a photosensitizer. This review summarizes recent developments of synthetically useful transformations promoted by the synergy between triplet ketone and transition-metal catalysis.

1 Introduction

2 Triplet Ketone Catalysis via Hydrogen Atom Transfer

2.1 Triplet Ketones with Nickel Catalysis

2.2 Triplet Ketones with Copper Catalysis

2.3 Triplet Ketones with Other Transition-Metal Catalysis

3 Triplet Ketone Catalysis via Single-Electron Transfer

4 Triplet Ketone Catalysis via Energy Transfer

5 Conclusions

Palladium hydrides are traditionally employed in hydrofunctionalization (i.e. monofunctionalization) of conjugated dienes and enynes, owning to its facile protic hydropalladation of electron‐rich (or neutral) unsaturated bonds. Herein, we report a mild PdH‐catalyzed difunctionalization of conjugated dienes and enynes. This protocol is enabled by the chemoselectivity switch of the initial hydropalladation step achieved by visible light enhancement of hydricity of PdH species. This method allows for cascade annulation of dienes and enynes with various easily available and abundant substrates, such as acrylic acids, acrylic amides, and Baylis–Hillman adducts, toward a wide range of alkenyl or alkynyl lactones, lactams, and tetrahydrofurans. This protocol also provides an easy access to complex spiro‐fused tricyclic frameworks.

Palladium hydrides are traditionally employed in hydrofunctionalization (i.e. monofunctionalization) of conjugated dienes and enynes, owning to its facile protic hydropalladation of electron‐rich (or neutral) unsaturated bonds. Herein, we report a mild PdH‐catalyzed difunctionalization of conjugated dienes and enynes. This protocol is enabled by the chemoselectivity switch of the initial hydropalladation step achieved by visible light enhancement of hydricity of PdH species. This method allows for cascade annulation of dienes and enynes with various easily available and abundant substrates, such as acrylic acids, acrylic amides, and Baylis–Hillman adducts, toward a wide range of alkenyl or alkynyl lactones, lactams, and tetrahydrofurans. This protocol also provides an easy access to complex spiro‐fused tricyclic frameworks.