Sodium tungstate-catalyzed “On-water” synthesis of β-arylvinyl bromides

Figures & data

Scheme 1.  “On-water’’ synthesis of E-vinyl bromides from β-aryl-α, β-eneoic acids.

Table 1. Synthesis of (E)-vinyl bromides from aromatic α,β-eneoic acids.

Figure 1.  Conformational equilibrium of methyl Z-2-bromo-5-phenylpent-2, 4-dienoate.

Table 2. Sodium tungstate-catalyzed bromodecarboxylation of cinnamic acid in aqueous medium in the presence of water-miscible co-solvents.

Entry	Amount of 30% H2O2 (mL)	Amount of water (mL)	Co-solvent	Amount of co-solvent (mL)	Reaction time^a (min)	Isolated yield (%)
1	2	2	NIL	NIL	30	80
2	2	0.5	Methanol	1.5	60	45
3	2	0.5	Acetone	1.5	60	40
4	2	0.5	DMF	1.5	60	5
^aAll the reactions were carried out using cinnamic acid (1 mmol), KBr (2 mmol), and NaWO4·2H2O (0.3 mmol) at room temperature.

Figure 2.  Catalytic role of sodium tetraperoxotungstate.

Figure 3.  Mechanistic explanation for the trans-stereoselectivity of bromodecarboxylation.

Figure 4.  Preferred decarboxylation of 2-cinnamylidenemalonic acid.