Synthesis and Reactivity of Uhle's Ketone and Its Derivatives

Uhle's ketone and its derivatives are highly versatile intermediates for the synthesis of a variety of 3,4-fused tricyclic indole frameworks, i.e. indole alkaloids of the ergot family, that are found in various bioactive natural products and pharmaceuticals. Therefore, the development of a convenient preparative method for this structural motif as well as its opportune/useful derivatization have been the subject of longstanding interest in the fields of synthetic organic chemistry and medicinal chemistry. Herein, we summarize recent and less recent methods for the preparation of Uhle's ketone and its derivatives as well as its main reactivity towards the synthesis of bioactive substances. Regarding the preparation, it can be roughly classified into two categories: (a) using 4-unfunctionalized and 4-functionalized indole derivatives as starting materials to construct a fused six-member ring, and (b) constructing the indole ring through intramolecular cycloaddition. Principally, the reactivity of the cyclic Uhle's ketone shown here is derived from the classical electrophilicity of the carbonyl carbon or the acidity of the alpha-hydrogen and, though less intensively investigated, chemical reactions that induce ring expansion to form novel ring skeletons. 1 Introduction 2 Synthesis 2.1 Disconnection A: Cyclization Reaction of the Opportune 3,4-Disubstituted Indole 2.2 Disconnection B: Intramolecular Friedel-Crafts Cyclization 2.3 Disconnection B: Intramolecular Cyclization via Metal-Halogen Exchange 2.4 Disconnection C: Intramolecular Diels-Alder Furan Cycloaddition 2.5 Disconnection D: Intramolecular Dearomatizing [3 + 2] Annulation 3 Reactivity 3.1 Use of Uhle's Ketone for Lysergic Acid 3.2 Use of Uhle's Ketone for Rearranged Clavines 3.3 Use of Uhle's Ketone for Medicinal Chemistry 4 Conclusion and Outlook

Automated summary

Uhle's ketone and its derivatives serve as versatile intermediates for synthesizing a variety of 3,4-fused tricyclic indole frameworks, which are important in the fields of synthetic organic chemistry and medicinal chemistry. The preparation methods can be roughly classified into two categories, and the reactivity mainly comes from the electrophilicity of the carbonyl carbon or the acidity of the alpha-hydrogen.