A simple and direct approach for the regioselective construction of the privileged 2H-indazole scaffold is described. The developed one-pot strategy involves phospholene-mediated N-N bond formation to access 2H-indazoles. The amount of organophosphorus reagent was minimized by recycling the phospholene oxide with organosilane reductants. Starting from functionalized 2-nitrobenzaldehydes and primary amines, a mild reductive cyclization, involving the use of commercially available phospholene oxide and silanes, delivered a wide variety of substituted 2H-indazoles in good to excellent yields.

A simple, regiocontrolled, and transition-metal-free approach to access exclusively 3-borylated thiophene derivatives is reported. The commercially available B-chlorocatecholborane reagent (ClBcat) acts as a carbophilic Lewis acid to activate the alkyne in readily synthesized (Z)-organylthioenyne substrates. This boron-induced activation initiates the formal thioboration and subsequent sulfur dealkylation, leading to the formation of 3-borylated thiophenes in good yields. The resulting borylated thiophenes are isolable as boronic esters (Bpin) and boronamides (Bdan). These borylated products are amenable to diverse downstream functionalization reactions, i.e., C−C bond formation through cross-coupling, azidation, bromination, and C−H activation.

A convenient and efficient strategy has been devised to access 3-amino-2H-indazole derivatives in two steps from readily available starting materials. The conversion of 2-nitrobenzonitriles to substituted benzamidines followed by an organophosphorus-mediated reductive cyclization and a subsequent N-N bond formation afforded 3-amino-2H-indazoles in good to excellent yields.

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The first synthesis of novel fused pyridazines has been realized starting from 1,3-diketones involving a Diaza-Wittig reaction as a key step. A convenient strategy was elaborated to access versatile pyridazine derivatives allowing the variation of substituents at position 6 of the heterocyclic ring. In a first part, pyridazines bearing an ester group were synthesized as a model to evaluate the methodology. In a second part, an improved procedure has been used for the synthesis of pyridazines bearing a ketone group and different methods of cyclization were carried out, leading to several hitherto unknown biheterocyclic compounds. This reaction scheme represents an attractive methodology for the synthesis of novel fused pyridazine derivatives.