Optimized Synthesis of 7-Azaindazole by a Diels–Alder Cascade and Associated Process Safety

Synthesis of Highly Functionalized 4-Iodo-7-azaindazoles via Condensation/Diels-Alder/Retro-Diels-Alder Cyclization of Iodoalkynones and 2-Hydrazineylpyrimidines

A method for the preparation of highly functionalized 4-iodo-7-azaindazoles is reported. These valuable heterocycles are synthesized via condensation of 2-hydrazineylpyrimidines with various iodoalkynones followed by Diels-Alder/retro-Diels-Alder cyclization. The method is general to the formation of products with a variety of C3, C5, and C6 substituents while preserving the C4 iodide functional handle for further late-stage functionalization. The utility of this transformation is demonstrated through the rapid synthesis of several bioactive azaindazole targets.

Divergent Synthesis of 6- or 7-Aza-Indazoles via Intramolecular Diels-Alder Cascade of Pyrazines

Pyrazines are reactive 4π partners in intermolecular Diels-Alder cycloaddition with exceptionally activated dienophiles or in an intermolecular version at elevated temperatures. Herein, it is shown that an intramolecular cascade could occur even at room temperature, delivering a collection of 6- or 7-aza-indazoles. An interesting substituent effect of the cycloaddition precursor on the product distribution was uncovered, and in situ NMR studies were conducted to gain insights into this unexpected selectivity.

Synthesis and Physicochemical Properties of 2-SF5-(Aza)Indoles, a New Family of SF5 Heterocycles

Structural diversity in heterocyclic chemistry is key to unlocking new properties and modes of action. In this regard, heterocycles embedding emerging fluorinated substituents hold great promise. Herein is described a strategy to access 2-SF₅-(aza)indoles for the first time. The sequence relies on the radical addition of SF₅Cl to the alkynyl π-system of 2-ethynyl anilines followed by a cyclization reaction. A telescoped sequence is proposed, making this strategy very appealing and reproducible on a gram scale. Downstream functionalizations are also demonstrated, allowing an easy diversification of N- and C3-positions. Ames test, pK _a, log P, and differential scanning calorimetry measurements of several fluorinated 2-Rf-indoles are also disclosed. These studies highlight the strategic advantages that a C2-pentafluorosulfanylated motif impart to a privileged scaffold such as an indole.