Coupling Stille: aryl triflate + organostannane

Echavarren, A. M., Stille, J. K. Palladium-catalyzed carbonylative coupling of aryl triflates with organostannanes. J. Am. Chem. Soc. 1988, 110, 1557-1565. 

In 2010 Nilsson and his group described the carbonylative Stille coupling of aryl triflates and aryl bromides with organostannanes by using Mo(CO)6 as a CO source [72]. Various ketones were synthesized in good yields in closed vessels at 100 °C (Scheme 4.35). In this case, DBU was needed to accelerate the release of CO from Mo(CO)e. 

In the model studies toward the total synthesis of dimethyl sulfomycinamate, Kelly et al. successfully carried out the Stille couplings of oxazolyl triflate 18 with an array of organostannanes [19, 20]. Thus, 2-aryl-4-oxalone 17 was transformed into the corresponding triflate 18, which was then coupled with 2-trimethylstannylpyridine under the agency of Pd(Ph3P)4 and LiCl to provide adduct 19. The couplings of triflate 18 with phenyl-, vinyl- and phenylethynyl trimethyltin all proceeded in excellent yields. Unfortunately, application to the more delicate system in the natural product failed and the oxazole moiety was installed from acyclic precursors. 

Like most aryl halides, furyl halides and furyl triflates have been coupled with a variety of organostannanes including alkenyl, aryl, and heteroaryl stannanes in the presence of catalytic palladium. Carbamoylstannane 66 was prepared by treating lithiated piperidine with carbon monoxide and tributyltin chloride sequentially. The Stille reaction of 66 and 3-bromofuran then gave rise to amide 67 [61]. In another example, lithiation of 4,4-dimethyl-2-oxazoline followed by quenching with MesSnCl resulted in 2-(tributylstannyl)-4,4-dimethyl-2-oxazoline (68) in 70-80% yield [62], Subsequent Stille reaction of 68 with 3-bromofuran afforded 2-(3 -furyl)-4,4-dimethyl-2-oxazoline (69). 

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