3-Alkylated anisole complexes of pentaammineosmium(II) are treated with methyl vinyl ketone and triflic acid to form 4H-anisolium Michael adducts. These compounds deprotonate regioselectively at the benzylic position adjacent to C3 and then undergo an aldol cyclization with the pendant carbonyl to form the decalin core. Reduction of the dienonium product can be directed in a 1,4 fashion to generate a trans decalin or in a 1,2 fashion to provide a methoxydiene complex that serves as a precursor to other functionalized decalins.