wt/vol

 

wt/vol

MW

moles

density

equivs.

yield

I

3.862 g

272.19

0.0142

 

1.0

 

II

3.401 g

218.10

0.0156

 

1.1

 

III

0.328 g

1,155.58

0.0003

 

0.02

 

IV

2.245 g

138.21

0.0162

 

1.1

 

V

20 mL

-

-

 

 

 

VI

80 mL

-

-

 

 

 

VII

3.847 g

283.38

0.0136

 

 

(96%)

 

Procedure:  250 mL 1-neck flask, stirbar, septum, condenser, N2 inlet

                  Dissolved 3.862 g of I and 3.401 g of II in 80 mL of dioxane and 20 mL of water.  Stirred at rt.  Added 2.245 g of K2CO3 followed by 0.328 g of (Ph3P)4Pd.  Heated to reflux.  After 7 h, TLC (10:90 EtOAc-hexanes, UV) showed product spot at Rf 0.59.  The reaction mixture was cooled to rt and the dioxane was removed by rotary evaporation.  The residue was poured into water and extracted with CH2Cl2.  The organic layer was dried over MgSO4, filtered and the solvent was removed by rotary evaporation.  The product was isolated by flash chromatography on silica gel using 10:90 EtOAc-hexanes as eluant.  The product was a clear, colorless oil.

 

1H NMR (CDCl3, 300 MHz) d 8.13 (d, J = 7.7 Hz, ArH), 7.33 (m, ArH), 7.18 (d, J = 6.6 Hz ArH), 7.08 (m, ArH), 6.12 (s, NH), 2.10 (s, ArCH3), 1.45 (s, C(CH3)3). 

 

notes

 

Catalytic Cycle for the Suzuki Coupling...

The oxidative addition step is generally the rate limiting step in the reaction

The oxidative addition step is generally the rate limiting step in the reaction.  The reactivity of the addition to the Pd(0) complex decreases on the order of I > OTf > Br >> Cl and the incorporation of electron withdrawing groups tends to increase the reactivity. 

 

The role of the base in the reaction serves to either quaternize the arylboronate or displace halide from the Pd(II) intermediate, both of which might facilitate transmetalation.