Arylation of β-methallyl alcohol catalyzed by Pd(OAc)2 in combination with P(t-Bu)3: application to fragrance synthesis

Pd(OAc)2 in combination with P(t-Bu)3 catalyzes the coupling of b-methallyl alcohol with 1-bromo-3,4-(methylenedioxy)benzene (1a), 1-bromo-4-methoxybenzene (1b), or 1-bromo-4-tert-butylbenzene (1c). The reaction affords the corresponding 2-methyl-3-aryl-propanals, which are valuable floral fragrances. With 1a or 1b high reaction rates are obtained at 130 C using NMP/water mixtures and an inorganic base such as Na2CO3. The chemoselectivity of the reaction is almost complete, so that the process appears practically feasible. In contrast, the coupling of b-methallyl alcohol with 1c proceeds with low reaction rates.