Recent Developments in Palladium-Catalyzed Formation of Five- and Six-Membered Fused Heterocycles

Abstract

Palladium-mediated cyclization reactions have been recognized as some of the simplest and useful tools for regio-as well as stereoselective syntheses of carbo-and heterocyclic compounds. In the multi-step syntheses of natural products it is frequently used as one of the most important steps. In this review article, we have summarized the various ways of constructing five-and six-membered heterocyclic rings by palladium-catalyzed intramolecular cyclizations published between 2008 and 2010.

Palladium‐Catalyzed Route to Three‐Component, One‐Pot Sequential Synthesis of Functionalized Cyclazines: 2,2a1,4‐Triazacyclopenta[cd]indenes

“…Recently, isocyanide‐based multicomponent reactions (IMCR) followed by other synthetic transformations have emerged as a powerful tool for creating fused multicyclic skeletons 1a–c. As a part of our program to discover novel heterocycles as antitumor agents and encouraged by the skeletal diversity of N‐rich polycyclic compounds,1e,3 we envisaged that 2,2a 1 ,4‐triazacyclopenta[ cd ]indene might be synthesized from halogen intermediate A (Figure 1, C), which itself could be prepared from 6‐bromopyridin‐2‐amine, an aldehyde and an isocyanide via a Groebke–Blackburn–Bienaymé (GBB) reaction,4 followed by in situ transition metal‐catalyzed intramolecular cyclization to afford this polycyclic heterocycle (Figure 1, C). The final cyclization step is essentially a palladium‐catalyzed α‐arylation of an activated C α H group of an α‐amino ester 5.…”

Rapid, two-pot procedure for the synthesis of dihydropyridinones; total synthesis of aza-goniothalamin

“…Six-membered nitrogen heterocycles are prevalent in many naturally occurring and biologically active compounds. As a result, their synthesis has received extensive research and wide spread publication in the literature [1][2][3][4][5][6]. Dihydropyridinones are an important subclass of heterocycles, which often feature both as useful intermediates, and as interesting species in their own right [7][8][9][10][11][12][13].…”

Switchable selectivity in Pd-catalyzed [3 + 2] annulations of γ-oxy-2-cycloalkenones with 3-oxoglutarates: C–C/C–C vs C–C/O–C bond formation

“…In the past decades, palladium chemistry has gained an important place in the toolbox of chemists, and its use became a privileged strategy for the selective formation of carbon–carbon and carbon–heteroatom bonds [2–5]. Among the different types of palladium-catalyzed transformations, domino – alias cascade – transformations [6–11] as well as annulation reactions [12–15] occupy a special place as they facilitate the synthesis of a variety of complex cycles in a single synthetic operation, through sequential and mechanistically independent bond-forming steps.…”