Dearomatizing Cyclization of 2-Iodoindoles by Oxidative NHC Catalysis to Access Spirocyclic Indolenines and Oxindoles Bearing an All Carbon Quaternary Stereocenter

Organocatalytic Asymmetric Construction of Spirooxazines via Chemoselective Cascade Addition of N-Substituted Hydroxylamine with Keto-bis-enone

Spirooxazines represent a privileged heterocyclic scaffold having pronounced biological importance. Herein, we introduce a chiral bifunctional squaramide catalyzed highly chemoselective cascade reaction involving aza-Michael/1,2-addition/oxa-Michael addition of N-substituted hydroxylamine with keto-bis-enones. This strategy enables the synthesis of highly enantioenriched oxa-spirooxazines with a broad substrate tolerance. Scalability and synthetic transformation have demonstrated the feasibility of the protocol. Furthermore, control experiments provided insights into the reaction mechanism.

A divergent intermediate strategy yields biologically diverse pseudo-natural products

The efficient exploration of biologically relevant chemical space is essential for the discovery of bioactive compounds. A molecular design principle that possesses both biological relevance and structural diversity may more efficiently lead to compound collections that are enriched in diverse bioactivities. Here the diverse pseudo-natural product (PNP) strategy, which combines the biological relevance of the PNP concept with synthetic diversification strategies from diversity-oriented synthesis, is reported. A diverse PNP collection was synthesized from a common divergent intermediate through developed indole dearomatization methodologies to afford three-dimensional molecular frameworks that could be further diversified via intramolecular coupling and/or carbon monoxide insertion. In total, 154 PNPs were synthesized representing eight different classes. Cheminformatic analyses showed that the PNPs are structurally diverse between classes. Biological investigations revealed the extent of diverse bioactivity enrichment of the collection in which four inhibitors of Hedgehog signalling, DNA synthesis, de novo pyrimidine biosynthesis and tubulin polymerization were identified from four different PNP classes.

Substrate-Controlled Diastereo- and Enantiodivergent Synthesis of Bis-Spirocyclopropyloxindoles from Available Isatin as a Single Starting Material

The first diastereo- and enantiodivergent asymmetric synthesis of new bis-spirocyclopropyloxindole scaffolds has been accomplished from the readily available isatin as a single starting material. Four rel-(1R,2R,3R), rel-(1S,2S,3R), rel-(1R,2R,3S), and rel-(1S,2S,3S) configurations of desired products were constructed in excellent enantiopurity via a simple switch in substrates using the chiral auxiliary-controlled method. The absolute configuration of cycloadducts with three contiguous quaternary/tertiary stereogenic centers was confirmed through X-ray diffraction analysis. A facile synthesis of versatile precursor 3-chlorooxindoles was also introduced.