Palladium(II)-Catalyzed Oxidative Transformation of Allylic Alcohols and Vinyl Ethers into 2-Alkoxytetrahydrofurans: Catechol as an Activator of Catalyst
[chemical reaction: see text]. A highly effective synthesis of 2-alkoxytetrahydrofurans from allylic alcohols and vinyl ethers was achieved by using catalytic amounts of Pd(OAc)2, Cu(OAc)2, and catechol (1:1:2) under O2. The use of catechol as an activator of Pd(II)-Cu(II) catalyst has been unprecedented. The 2-alkoxytetrahydrofurans are formed via oxypalladation of allylic alcohols toward vinyl ethers
Catalytic amounts of cobalt complexes 2 and 3 are capable of generating alkyl radicals from the corresponding bromides under mild readion conditions, allowing the selective preparation of either saturated or unsaturatedradicalcyclization products.
The reaction of (E)- or (Z)-cinnamyl alcohol and ethyl vinylether with a catalyst consisting of Pd(OAc) 2 , Cu(OAc) 2 , and catechol (1:1:2) under O 2 gives a good yield of(Z)- or (E)-4-benzylidene-2-ethoxytetrahydrofuran, respectively. Similarly, 2-butoxy-4-exomethylenetetrahydrofuran was obtained from allyl alcohol and butyl vinylether. In the case of allyl alcohol, however, the catalysis does