4-Quinolinyl triflate

The Stille coupling of an aryl triflate normally calls for the addition of at least one equivalent of LiCl. Presumably, the transmetallation is facilitated by replacing triflate with CP at the palladium intermediate generated from oxidative addition. As Stille demonstrated in 1988, 4-quinolinyl triflate 100 was coupled with phenylstannane 101 in the presence of Pd(Ph3P)4 and LiCl in refluxing 1,4-dioxane to furnish biaryl 102, which was used as an intermediate for the first total synthesis of antibiotic amphimedine (88JA4051). 

Interestingly, 4-quinolinyl triflate 103 underwent the Stille coupling smoothly with 3-tributylstannylindole 104 to deliver indolylquinoline 105 in 92% yield in the presence of Pd2(dba)3-AsPh3 in the absence of LiCl (94TL2405). It is possible that this transmetallation is facilitated by the softer ligand AsPh3. 

Both vinyl- and aryl triflates have been cross-coupled with 2-furylzinc chloride [26-28]. Since vinyl triflates are easily obtained from the corresponding ketones, they are useful substrates in Pd-catalyzed reactions. In the following example, a Negishi coupling of 2-furylzinc chloride and indol-5-yl triflate (22) provided an expeditious entry to 2-(5 -indolyl)furan (23). Protection of the NH in the indole ring was not required. A similar reaction was successful with pyridyl- and quinolinyl triflates. 

Quinolinyl moiety has been applied in the Negishi reaction either as an electrophile or as nucleophile. 2- or 4-substituted quinolinyl triflates or bromides have been used extensively for introduction of aromatic rings at the C2 or C4 positions of the heterocycle. In a representative example, Murata et al. employed a Negishi reaction in his effort toward the formal synthesis of antitumor compound camptothecin. In accordance to that, 2-chloropyridine was allowed to react with lithium naphthalenide, followed by zinc chloride, to afford the corresponding zinc pyridine salt. Reaction of the resulting organozinc intermediate with 2-chloro-3-quinoline carboxylate provided the hetero biaryl core of camptothecin. ... 

In 2002, Nikolaides et al. reported the coupling of quinolinyl-8-triflate with Et4Sn to synthesize 8-ethylquinoline in 74% yield (2002SC2027). 

Heck Reactions. The Heck reaction is a Pd-catalyzed olefi-nation usually performed between an aryl halide or triflate and an acrylate ester. While phosphines are traditionally used as ancillary ligands, new Pd(dba)2-mediated reactions have been performed with a variety of other ligand types. These include chelating Wheterocyclic carbene/phosphine ligands, benzimidazoles, and quinolinyl oxazolines. Air stable catalysts have been prepared from Pd(dba)2 and sterically hindered thiourea ligands (eq 24). An effective immobilized catalyst has been prepared from Pd(dba)2 and a dendritic phosphine-containing polymer. ... 

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