Palladium(II)-Catalyzed Intramolecular Oxidative C-H/C-H Cross-Coupling Reaction of C3,N-Linked Biheterocycles: Rapid Access to Polycyclic Nitrogen Heterocycles.

A Pd(II)-catalyzed intramolecular oxidative C-H/C-H cross-coupling has been developed for the direct construction of valuable polycyclic heteroarene scaffolds. From a retrosynthetic point of view, the strategic formation of a C-C bond via C(sp2)-H/C(sp2)-H dehydrogenative coupling across C3,N-linked biheterocyclic precursors may be useful in de novo syntheses of indole-derived natural products and pharmaceuticals. The reaction exhibited good functional group/heterocycle tolerance, and a proposed mechanism involving an azoylpalladium complex is also supported.

Divergent construction of pyrazoles via Michael addition of N-arylhydrazones to 1,2-diaza-1,3-dienes.

The base (NaH)-promoted Michael addition of N-arylhydrazones (AHs) with 1,2-diaza-1,3-dienes (DDs) produces unprecedented ß-azohydrazone adducts. Strategically, the use of AHs as acyl anion equivalents (d(1) synthon) and DDs as α-electrophiles (a(2) synthon) of carbonyl compounds open the way to two important classes of pyrazole compounds.

Interceptive [4 + 1] annulation of in situ generated 1,2-diaza-1,3-dienes with diazo esters: direct access to substituted mono-, bi-, and tricyclic 4,5-dihydropyrazoles.

In situ derived acyclic and cyclic 1,2-diaza-1,3-dienes (DDs) were engaged in interceptive [4 + 1] annulation strategy with diazo esters (DEs). The catalytic activity of inexpensive copper(II) chloride allows the direct synthesis of mono-, bi-, and tricyclic 4,5-dihydropyrazole-5-carboxylic acid derivatives in a process that circumvents the use of an anhydrous and inert atmosphere.