10. Patented Literature 2616 10.1. Esterification 2616 10.2. Ether Formation 2619 10.2.1. Etherification without Cyclization 2619 10.2.2. Etherification with Cyclization 2624 10.3. N-Alkylation 2625 10.4. Other Reactions 2627 11. Summary and Outlook 2628 12. Note Added in Proof 2628 13. Abbreviations Used in This Review 2629 14. Acknowledgments 2629 15. Supporting Information Available 2630 16. References 2630

Mitsunobu and Related Reactions: Advances and Applications

Research and industrial interest in radical C–H activation/radical cross-coupling chemistry has continuously grown over the past few decades. These reactions offer fascinating and unconventional approaches toward connecting molecular fragments with high atom- and step-economy that are often complementary to traditional methods. Success in this area of research was made possible through the development of photocatalysis and first-row transition metal catalysis along with the use of peroxides as radical initiators. This Review provides a brief and concise overview of the current status and latest methodologies using radicals or radical cations as key intermediates produced via radical C–H activation. This Review includes radical addition, radical cascade cyclization, radical/radical cross-coupling, coupling of radicals with M–R groups, and coupling of radical cations with nucleophiles (Nu).

Recent Advances in Radical C-H Activation/Radical Cross-Coupling.

The association of an electron-rich substrate with an electron-accepting molecule can generate a new molecular aggregate in the ground state, called an electron donor–acceptor (EDA) complex. Even w...

https://pubs.acs.org/doi/pdf/10.1021/jacs.0c01416

Synthetic Methods Driven by the Photoactivity of Electron Donor-Acceptor Complexes

Recent Advances in the Stereoselective Synthesis of Tetrahydrofurans.

We demonstrate the application of ligand-to-metal charge transfer (LMCT) excitation to the direct catalytic generation of energetically challenging alkoxy radicals from alcohols through a coordination–LMCT–homolysis process with an abundant and inexpensive cerium salt as the catalyst. This catalytic manifold provides a simple and efficient way to utilize the characteristic reactivity and selectivity of transient alkoxy radicals for δ-selective C–H bond functionalization. Under mild redox-neutral conditions without the need for prefunctionalization, this method provides a versatile platform to access molecular complexity from simple and abundant alcohols.

δ-Selective Functionalization of Alkanols Enabled by Visible-Light-Induced Ligand-to-Metal Charge Transfer.

In recent years, powerful new methods for the generation of alkoxyl radicals under mild and neutral conditions have been developed. This progress has led to a thorough investigation of most O-radical elementary reactions.Today, sufficiently reliable thermodynamic and kinetic data are available either from experimental or from theoretical studies in order to predict alkoxyl radical reactivities and selectivities in synthesis. For instance, alkoxyl radicals readily add to carbon-carbon and carbon-nitrogen double bonds. Due to generally low activation barriers and strongly negative reaction enthalpies, inter- and intramolecular addition reactions proceed under kinetic control and are associated with high rate constants. Nevertheless, intramolecular 5-exo-trig additions, i.e. cyclizations, proceed with an astonishing degree of diastereoselectivity and often provide complementary selectivities if compared to commonly used methods such as the bromine cyclization of alkenols. Therefore, several useful applications of O-radical cyclizations in the synthesis of functionalized tetrahydrofurans have been discovered in the last few years. A second major reaction channel of alkoxyl radicals is associated with the homolysis of a β-C-C bond. This fragmentation proceeds under thermodynamic control and affords a carbonyl compound besides an alkyl radical from the starting alkoxyl radical. Regioselectivities for C-C bond homolysis may be predicted by considering strain release (cyclic carbon framework) and the stability of the newly formed carbon radical (cyclic and open chain carbon skeletons). The third major group of alkoxyl radical-based transformations are connected with homolytic substitutions such as intramolecular 1,5-hydrogen shifts which have been applied with considerable success to remote functionalization reactions. In view of the diversity of alkoxyl radical reactions it is the aim of this review to organize basic principles of this type of chemistry and to present its latest useful application in organic synthesis.

Selectivity in the chemistry of oxygen-centered radicals: The formation of carbon-oxygen bonds

Tertiary alkoxyl radicals from 3-alkoxythiazole-2(3H)-thiones

Efficiency of alkoxyl radical product formation from 5-substituted 3-alkoxy-4-methylthiazole-2(3H)-thiones

Visible light-initiated or thermally induced N-O homolysis of hitherto unknown 4-methyl-5-(p-anisyl)-substituted N-alkoxythiazolethiones furnishes alkoxyl radicals, which have been applied in the diastereoselective synthesis of bicyclic tetrahydrofuran rac-5 (5-exo-trig cyclization), formation of erythrose derivative 8 (β-C,C cleavage), and the preparation of bromoalcohol 10 (via selective 1,5-H-translocation), optionally under tin-free conditions.

N-Alkoxy-4-methyl-5-(p-anisyl)thiazole-2(3H)thiones - New Precursors for Visible Light- or Thermally-Induced Alkoxyl Radical Reactions in Synthesis

Cyclopentyl and Carbohydrate Derivatives of N-Hydroxy-4-methylthiazole-2(3H)-thione: Synthesis by Mitsunobu Reaction and Highly Selective Photochemical Conversion into Aldehydes

Thomas Gottwald

Papers

Selectivity in the chemistry of oxygen-centered radicals: The formation of carbon-oxygen bonds

Tertiary alkoxyl radicals from 3-alkoxythiazole-2(3H)-thiones

Efficiency of alkoxyl radical product formation from 5-substituted 3-alkoxy-4-methylthiazole-2(3H)-thiones

N-Alkoxy-4-methyl-5-(p-anisyl)thiazole-2(3H)thiones - New Precursors for Visible Light- or Thermally-Induced Alkoxyl Radical Reactions in Synthesis

Cyclopentyl and Carbohydrate Derivatives of N-Hydroxy-4-methylthiazole-2(3H)-thione: Synthesis by Mitsunobu Reaction and Highly Selective Photochemical Conversion into Aldehydes