DBU-Mediated [3+3] Annulation of Indolin-3/2-ones and Ethenesulfonyl Fluorides: An Approach to Indole-Fused δ-Sultones

A general and efficient approach to the synthesis of various indole-fused δ-sultones has been developed via DBU-mediated [3+3] cyclizations of indolin-3/2-ones and β-(hetero)arylethenesulfonyl fluorides. Notably, the reaction shows a broad substrate scope, and over 70 examples were exhibited in up to 99% isolated yield. In addition, some of the synthesized compounds showed significant antitumor activity against HepG2 and Caco-2 cells in vitro, which might provide promising insights for the future discovery and rational design of novel antitumor agents.

[3+2] Cycloaddition of Alkynyl Boronates and in situ Generated Azomethine Ylide

Scalable [3+2] cycloaddition of alkynyl boronates and in situ generated unstabilized azomethine ylide is reported for the first time. The selective formation of either 1 : 1 or 1 : 2 cycloaddition products was achieved by carefully optimizing the reaction conditions, mainly by controlling the reactant stoichiometry, catalyst loading, and internal temperature. The developed protocol tolerated many valuable functional groups, including TMS, protected alcohol (as ether or THP derivatives), or aldehyde (as acetal). Further common C-C and C-heteroatom bond-forming reactions, as well as scaled-up procedures demonstrate the utility of the prepared compounds as building blocks for organic synthesis and drug discovery.

Chemoselective Reactions of Functionalized Sulfonyl Halides

Chemoselective transformations of functionalized sulfonyl fluorides and chlorides are surveyed comprehensively. It is shown that sulfonyl fluorides provide an excellent selectivity control in their reactions. Thus, numerous conditions are tolerated by the SO2 F group - from amide and ester formation to directed ortho-lithiation and transition-metal-catalyzed cross-couplings. Meanwhile, sulfur (VI) fluoride exchange (SuFEx) is also compatible with numerous functional groups, thus confirming its title of "another click reaction". On the contrary, with a few exceptions, most transformations of functionalized sulfonyl chlorides typically occur at the SO2 Cl moiety.

Radical 1-Fluorosulfonyl-2-alkynylation of Unactivated Alkenes

Sulfonyl fluorides have found widespread use in chemical biology and drug discovery. The development of synthetic methods for the introduction of the sulfonyl fluoride moiety is therefore of importance. Herein, a transition-metal-free radical 1,2-difunctionalization of unactivated alkenes via FSO2 -radical addition with subsequent vicinal alkynylation to access β-alkynyl-fluorosulfonylalkanes is presented. Alkynyl sulfonyl fluorides are introduced as highly valuable bifunctional radical trapping reagents that also serve as FSO2 -radical precursors. The β-alkynyl-fluorosulfonylalkanes obtained in these transformations can be readily diversified by using SuFEx click chemistry to obtain sulfonates and sulfonamides.

A Close-up Look at the Chemical Space of Commercially Available Building Blocks for Medicinal Chemistry

The ability to efficiently synthesize desired compounds can be a limiting factor for chemical space exploration in drug discovery. This ability is conditioned not only by the existence of well-studied synthetic protocols but also by the availability of corresponding reagents, so-called building blocks (BBs). In this work, we present a detailed analysis of the chemical space of 400 000 purchasable BBs. The chemical space was defined by corresponding synthons─fragments contributed to the final molecules upon reaction. They allow an analysis of BB physicochemical properties and diversity, unbiased by the leaving and protective groups in actual reagents. The main classes of BBs were analyzed in terms of their availability, rule-of-two-defined quality, and diversity. Available BBs were eventually compared to a reference set of biologically relevant synthons derived from ChEMBL fragmentation, in order to illustrate how well they cover the actual medicinal chemistry needs. This was performed on a newly constructed universal generative topographic map of synthon chemical space that enables visualization of both libraries and analysis of their overlapped and library-specific regions.

Diversity Oriented Clicking (DOC): Divergent Synthesis of SuFExable Pharmacophores from 2-Substituted-Alkynyl-1-Sulfonyl Fluoride (SASF) Hubs

Diversity Oriented Clicking (DOC) is a unified click-approach for the modular synthesis of lead-like structures through application of the wide family of click transformations. DOC evolved from the concept of achieving "diversity with ease", by combining classic C-C π-bond click chemistry with recent developments in connective SuFEx-technologies. We showcase 2-Substituted-Alkynyl-1-Sulfonyl Fluorides (SASFs) as a new class of connective hub in concert with a diverse selection of click-cycloaddition processes. Through the selective DOC of SASFs with a range of dipoles and cyclic dienes, we report a diverse click-library of 173 unique functional molecules in minimal synthetic steps. The SuFExable library comprises 10 discrete heterocyclic core structures derived from 1,3- and 1,5-dipoles; while reaction with cyclic dienes yields several three-dimensional bicyclic Diels-Alder adducts. Growing the library to 278 discrete compounds through late-stage modification was made possible through SuFEx click derivatization of the pendant sulfonyl fluoride group in 96 well-plates-demonstrating the versatility of the DOC approach for the rapid synthesis of diverse functional structures. Screening for function against MRSA (USA300) revealed several lead hits with improved activity over methicillin.

Light-induced [2 + 2] cycloadditions for the construction of cyclobutane-fused pyridinyl sulfonyl fluorides

Cyclobutanes are an important class of motifs present in a wide range of natural products and other biologically significant molecules. A photocatalytic [2 + 2] cycloaddition between pyridones or isoquinolones and ethenesulfonyl fluoride was achieved, providing a portal to a class of unique cyclobutane-fused pyridinyl sulfonyl fluorides with quaternary rigid rings (30 examples). Further applications of these novel sulfonyl fluoride molecules in SuFEx click chemistry were also accomplished, providing the corresponding sulfonates and sulphonamides with reasonable yields.

Applications of 2-Chloro-3,3,3-trifluoroprop-1-ene (HCFO-1233xf): A Rapid Entry to Various β-Substituted-trifluoromethyl-ethenes

An efficient base-promoted reaction of O-, N-, and S-nucleophiles with 2-chloro-3,3,3-trifluoprop-1-ene (HCFO-1233xf) is described providing access to various β-substituted-trifluoromethyl-ethenes under mild reaction conditions. Mechanistic investigations shed some light on the regio-, chemo-, and stereoselectivities observed. The olefins prepared represent attractive intermediates in chemical discovery: some applications include their conversion to pyrrolidines via a [3 + 2] dipolar cycloaddition reaction. These weakly basic amines represent novel synthons that could be readily elaborated through a range of reactions.

The growing applications of SuFEx click chemistry

SuFEx (Sulfur Fluoride Exchange) is a modular, next generation family of click reactions, geared towards the rapid and reliable assembly of functional molecules.

Chemoselective cyclization of N-sulfonyl ketimines with ethenesulfonyl fluorides: access to trans-cyclopropanes and fused-dihydropyrroles

A stereo- and chemoselective ring closing reaction of N-sulfonyl ketimines with ethene sulfonyl fluorides promoted by DBU is reported. This selective C–C vs. C–N bond cyclization process delivers to trans-cyclopropanes (dr up to ≤99 : 1) and fused-dihydropyrroles.