Identifying a Hidden Conglomerate Chiral Pool in the CSD

Conglomerate crystallization is the spontaneous generation of individually enantioenriched crystals from a nonenantioenriched material. This behavior is responsible for spontaneous resolution and the discovery of molecular chirality by Pasteur. The phenomenon of conglomerate crystallization of chiral organic molecules has been left largely undocumented, with no actively curated list available in the literature. While other crystallographic behaviors can be interrogated by automated searching, conglomerate crystallizations are not identified within the Cambridge Structural Database (CSD) and are therefore not accessible by conventional automated searching. By conducting a manual search of the CSD and literature, a list of over 1800 chiral species capable of conglomerate crystallization was curated by inspection of the racemic synthetic routes described in each publication. The majority of chiral conglomerate crystals are produced and published by synthetic chemists who seldom note and rarely exploit the implications this phenomenon can have on the enantiopurity of their crystalline materials. With their structures revealed, we propose that this list of compounds represents a new chiral pool which is not tied to biological sources of chirality.

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 α-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

Concise catalytic asymmetric synthesis of (R)-4-amino Uhle's ketone

A practical and asymmetric synthesis of (R)-4-amino-5-oxo-1,3,4,5-tetrahydrobenz[cd]indole, an enantiopure framework shared by most ergot alkaloids, was accomplished. Our method involves a Rh(i)-catalyzed 6-exo-trig intramolecular cyclization of an appropriate 4-pinacolboronic ester d-tryptophan aldehyde followed by the oxidation of the resulting secondary benzylic alcohol with a Cu(i)-ABNO catalyst and final deprotection under acidic conditions. This new procedure offers significant advantages over previous synthetic approaches, including brevity, mild reaction conditions, preservation of chiral integrity, and high overall yield and avoids the use of stoichiometric amounts of strongly basic and pyrophoric organometallic reagents.

Access to Polycyclic Azepino[5,4,3-cd]indoles via a Gold-Catalyzed Post-Ugi Dearomatization Cascade

The development of a rapid and diverse access to complex natural product-like 3,4-fused indole scaffolds has always attracted considerable attention from synthetic and medicinal communities. We herein disclose a modular and straightforward protocol to prepare the densely substituted polycyclic azepino[5,4,3-cd]indole scaffolds. This synthetic process involves an Ugi four-component reaction from easily available starting materials and a gold-catalyzed post-Ugi domino dearomatization/Michael addition sequence, enabling facile access to the highly functionalized azepino[5,4,3-cd]indole core with excellent chemo-, regio-, and diastereoselectivity.

One pot synthesis of pyrrolo[3,2,1-de]phenanthridines from 7-phenylindoles via tandem C–H olefination/aza-Michael addition

An unprecedented one-pot C–H olefination/aza-Michael addition tandem process has been developed for the synthesis of pyrrolo[3,2,1-de]phenanthridines from 7-phenylindoles and alkenes using a [Cp*RhCl₂]₂/AgOAc/Me₄NOAc catalytic system.