C−C Bond Formation via C−H Bond Activation:  Synthesis of the Core of Teleocidin B4

Abstract

The core of teleocidin B4, a complex fragment of a natural product containing two quaternary stereocenters and a penta-substituted benzene ring, was synthesized in four C-C bond-forming steps starting from tert-butyl derivative 1. The first step involved alkenylation of the tert-butyl group with a vinyl boronic acid, followed by the successful annulation of the cyclohexane ring to the benzene nucleus via an intramolecular Friedel-Crafts reaction. The third step required a diastereoselective oxidative carbonylation of the geminal dimethyl group, followed at last by indole assembly via the alkenylation of the phenol nucleus, to afford the teleocidin B4 core. Noteworthy is the fact that steps 1 and 3 critically depended on the directing role of the aniline nitrogen (directed C-H bond functionalization).

Palladium(II)‐katalysierte C‐H‐Aktivierung/C‐C‐Kreuzkupplung: Vielseitigkeit und Anwendbarkeit

“…[52] Über ein einziges Beispiel für eine stöchiometrische Kupplung eines cyclopalladierten Komplexes mit Vinylboronsäure wurde zuvor auch von Sames et al berichtet. [63] Unsere ersten Ergebnisse zeigten, dass die Kupplung von Oxazolinsubstraten mit Organoboronsäuren etwa 10 % Ausbeute ergab. Bei der Untersuchung anderer dirigierender Gruppen gelang uns auch die Kupplung von Pyridinsubstraten mit Alkylboronsäuren (Schema 41).…”

Catalytic Methods for CH Bond Functionalization: Application in Organic Synthesis

“…(57). [115] In this reaction, Ph 2 Si(OH)Me shows a high reactivity. The Pd(OAc) 2 -catalyzed phenylation of a tert-butyl group in an aromatic Schiff base with the diphenylsilanol proceeded in good yield.…”

σ-Alkenyl endo-palladacycle formation via regiospecific functionalisation of an unreactive NHC-tethered C(sp2)–H bond

“…In light of such governing parameters, the majority of cyclometallated complexes are restricted to form via C(sp 2 )-H activation at an aromatic carbon (Figure 1 A), or C(sp 3 )-H activation at an aliphatic or benzylic carbon atom (Figure 1 B). 14,15 Whilst C(sp 3 )-H activation is a rapidly expanding field of research, the direct activation of non-acidic, non-aromatic sp 2 -hybridised C-H bonds is far less explored. Investigations in our laboratory focus on the reactivity and applications of Nheterocyclic carbenes (NHCs) as ancillary ligands for a broad scope of chemical transformations.…”