Regioselective arylation of unsaturated silanes under phase transfer catalysis conditions

Selective synthesis of (E)-triethyl(2-arylethenyl)silane derivatives by reaction of aryl bromides with triethyl vinylsilane catalysed by a palladium–tetraphosphine complex

“…Then, we studied the influence of the base for the coupling of 4-t butylbromobenzene with vinyltriethylsilane. Disappointing low selectivities were also obtained using sodium carbonate, sodium hydrogen carbonate, cesium carbonate or potassium fluoride ( Table 1, entries [11][12][13][14]. On the other hand, a much higher selectivity in favour of the formation of (E)-4-(2-triethylsilanyl-vinyl)-tert-butylphenyl 6a was observed using sodium acetate as base ( Table 1, entry 15).…”

“…Oxidative addition to palladium should be slower with bromothiophenes, than with bromopyridines. 2-Bromo and 3-bromothiophenes with vinyltriethylsilane led to the vinylation E adducts 37a and 38a with high selectivities (92-95%) but with very low TONs of 100 and 140 (Table 4, entries [9][10][11][12]. With these substrates the oxidative addition is probably the rate-limiting step of the reaction, but a poisoning effects of the sulphur atom is also possible.…”

“…Similar reaction rates were obtained with electron-rich and electron-poor aryl bromide. For example, turnover numbers of 7500-10,000 can be achieved with this catalyst for activated substrates such as 4-bromoacetophenone, 4-bromobenzaldehyde, 4-bromobenzophenone, 4-bromobenzonitrile and 4-fluorobromobenzene ( Table 2, entries [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. With the deactivated aryl bromides: 4-t butylbromobenzene, 4-bromoanisole and 4-dimethylaminobromobenzene TONs of 5600, 7400 and 1000 were obtained, respectively ( Table 2, entries 24-27 and 30).…”

“…Tri-2-furylphosphine ligand in the presence of 2.5-5% Pd 2 (dba) 3 also catalyses the reaction of aryl iodides with 2-pyridyldimethyl(vinyl)silane [10,11]. The reaction of aryl iodides and vinylsilanes also proceeds with Pd(OAc) 2 without added ligand in the presence of tetraalkylammonium halide salts [12][13][14]. If monophosphine ligands have been successfully used for the Heck reaction of vinylsilanes, to the best of our knowledge, the efficiency of tetraphosphine ligands has not been demonstrated.…”