reaction was repeated using DMF/NaOH instead of water/NaOH at 140 °C under open air, where complete consumption of the starting bromide was noticed after only one hour (entry 2, Table 5). Using triethylamine as base and water as solvent resulted in full conversion after 4 h (entry 3, Table 5).
The Heck reaction was repeated for a deactivated bromide (4-bromoanisole 9) with styrene in DMF/NaOH in the presence of TBAB using 0.5 mol% of the Pd complex 7 at 140 °C for 2 h (based on TLC) to give 4-methyl-4'-nitrobiphenyl 36 in 87% yield (entry 4, Table 5). 4- Nitrobromobenzene 10 and 2-bromonaphthalene 11 were similarly cross-coupled with styrene in DMF or water in the presence of sodium hydroxide or triethylamine and the best results were obtained when DMF/NaOH/TBAB catalytic system was used (entries 6 and 8, Table 5).
Ar (Het) PhPh0.5 mol% Cat. 7solvent, base, TBAB34a+ 35-40Ar (Het)-Br8-13
Table 5. Heck cross coupling of aryl (heteroaryl) bromides with styrene
Entry
Ar(Het)-Br
Product
Base/solvent
Time(h)
Yield%a,b
1
2
3
BrO 8
OPh 35
NaOH/H2O
NaOH/DMF
Et3N/H2O
3
1
4
100 (92)
100
100
4
MeOBr 9
MeOPh36
NaOH/DMF
2
100 (87)
5
6
O2NBr10
O2NPh37
NaOH/H2O
NaOH/DMF
5
2
80
100 (95)
7
8
9
Br11
Ph 38
NaOH/H2O NaOH/DMF
Et3N /H2O
3
2
6
80
100 (90)
70
10
11
NBr 12
NPh 39
NaOH/DMF
NaOH/H2O
5
6
70
100 (88)
12
NBr13
NPh 40
NaOH/DMF
5
100 (90)
aConditions: Bromide/ styrene/ base/ TBAB/ solvent: 1/1.5/2/0.6/3 mL at 100 °C for water and at 140 °C for DMF. bValues in parenthesis refer to the isolated yields
3-Bromopyridine 12 and 3-bromoquinoline 13, as heterocyclic bromides, were similarly cross coupled with styrene to give the corresponding styryl derivatives 39 and 40, respectively.
