Highly substituted quinolones are obtained through an efficient and atom economical procedure that involves two consecutive palladium(II)‐catalyzed CH alkenylation reactions. A selective 6‐endo intramolecular CH alkenylation leads to 4‐substituted quinolones that have been further functionalized at C‐3 through a second intermolecular CH alkenylation reaction.magnified image

Palladium-catalyzed dehydrogenative coupling is an efficient synthetic strategy for the construction of quinoline scaffolds, a privileged structure and prevalent motif in many natural and biologically active products, in particular in marine alkaloids. Thus, quinolines and 1,2-dihydroquinolines can be selectively obtained in moderate-to-good yields via intramolecular C–H alkenylation reactions, by choosing the reaction conditions. This methodology provides a direct method for the construction of this type of quinoline through an efficient and atom economical procedure, and constitutes significant advance over the existing procedures that require preactivated reaction partners.

The Mizoroki–Heck reaction of N‐alkenyl‐substituted 2‐haloanilines is an effective protocol for the synthesis of substituted 4‐alkylidene‐tetrahydroquinoline derivatives, avoiding isomerization and oxidation. When non‐substituted alkenes are used, the regioselectivity of the reaction can be directed towards the formation of an exocyclic or endocyclic double bond by choosing an adequate catalytic system. When the double bond is substituted by an amide moiety, the exocyclic double bond of E geometry is obtained selectively. Thus, this protocol efficiently synthesizes a series of 2‐substituted tetrahydroquinolines with an exo α,β‐unsaturated amide moiety at the C‐4 position.

A protocol for the Pd(II)-catalyzed C−H alkenylation reaction of substituted N-allylanilines via an unusual 6-endo process has been developed. A density functional theory (DFT) study of the mechanistic pathway has shown that the coordination of the remote protecting group to the palladium center is determinant for the control of the regioselectivity in favor of the 6-endo process. The reaction would proceed via prior activation of the alkene. This procedure constitutes a mild and efficient method for the synthesis of 1,4-dihydroquinoline derivatives from simple and readily accessible substrates.

Highly substituted coumarins, privileged and versatile scaffolds for bioactive natural products and fluorescence imaging, are obtained via a Pd­(II)-catalyzed direct C–H alkenylation reaction (Fujiwara–Moritani reaction), which has emerged as a powerful tool for the construction and functionalization of heterocyclic compounds because of its chemical versatility and its environmental advantages. Thus, a selective 6-endo cyclization led to 4-substituted coumarins in moderate yields. Selected examples have been further functionalized in C3 through a second intermolecular C–H alkenylation reaction to give coumarin-acrylate hybrids, whose fluorescence spectra have been measured.