Aryl triflates with vinylstannane

The cross-coupling of aryl triflates with vinylstannanes gave a good yield of styrene derivatives with retention of the double-bond geometry in most cases. The reaction was applied to a synthesis of the quinoline alkaloid dubamine125 (equation 106). Other... 

For coupling, the cheaper aryl fluorosulfonate 713 is used as an alternative to the expensive aryl triflates to give the same results[473]. The arenesulfonates 714 are active for the reaction with vinylstannanes when dppp and LiCI are used in DMSO[583], The bromide 715 attacks the arylstannane moiety selectively without reacting with the organoboron moiety in 716 in the absence of a base[584]. 

Analogously, 5-tributylstannylimidazole 29 was easily obtained from the regioselective deprotonation of 1,2-disubstituted imidazole 28 at C(5) followed by treatment with tributyltin chloride [24]. In the presence of 2.6 equivalents of LiCl, the Stille reaction of 29 with aryl triflate 30 afforded the desired 1,2,5-trisubstituted imidazole 31 with 2,6-di-tert-butyl-4-methylphenol (BHT) as a radical scavenger. Reversal of the nucleophile and electrophile of the Stille reaction also provided satisfactory results. For example, the coupling reaction of 5-bromoimidazole 33, derived from imidazole 32 via a regioselective bromination at C(5), and vinylstannane 34 produced adduct 35 [24],... 

Palladium can also catalyze cross-coupling between aryl halides and aryl or vinylstannanes and there are examples of application of this reaction in the synthesis of pyrroles and indoles. 1-Tosyl-3-(tri-n-butylstannyl)indole gives good yields of coupling products with vinyl and aryl iodides and triflates. The recommended catalyst is tris-(dibenzylideneacetone)-dipalladium (5 mol%) used with triphenylarsine (10 mol%) (Equation (121)) <94TL2405>. 

Aryl halides (Br, I) have been converted in good yields into the corresponding arylstannanes or -silanes by treatment with RgSn2 (R = Bu, Me) or Hexamethyldisilane, respectively, in the presence of catalytic Pd(Ph3P)4 (eq 29). Aryl and vinyl triflates produce aryl- and vinylstannanes under similar conditions, provided Hexamethyldistannane and LiCl are used as co-reactants. In some cases, the presence of additional PhsP has been observed to improve yields. By using the (Ph3Sn)2Zn-TMEDA complex, vinyl halides can also be converted into vinylstannanes. ... 

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