STEREODEFINED TANDEM ADDITION-REACTIONS OF ETA(2)-ARENES - A VERSATILE ROUTE TO FUNCTIONALIZED CYCLOHEXENES

A series of anisoles are complexed by pentaammineosmium(II), and the r esulting 5,6-eta(2)-anisole complexes are treated with activated olefi ns or acetals in the presence of triflic acid to form 4H-anisolium com plexes. These intermediates are capable of undergoing inter- or intram olecular nucleophilic addition reactions at C3, and 2-methoxy-1,3-cycl ohexadiene complexes are formed. These complexes are readily converted into functionalized cyclohexenones, cyclohexadienes, and cyclohexenes . When BF3. OEt2 is used, it is possible to form a 4H-anisolium comple x with a pendent boron enolate, which can ultimately undergo intramole cular addition to C1 to form the corresponding [4 + 2] cycloadduct. Fo r cases in which an activated alkyne is added to a C4-alkylated anisol e, a migration of the vinyl group occurs, leading to 4-methyl-3-vinyla nisoles.