Scheme 3.

exo-Selective ruthenium(0) catalyzed [4+2] cycloaddition of cyclohexadiene.^a

^aYields are of material isolated by silica gel chromatography. dppe = bis-(diphenylphosphino)ethane. ^bThe cis-1,2-diol was employed. ^cA mixture of cis- and trans-1,2-diols was employed. ^drac-BINAP (6 mol%), BINAP = 2,2′-bis-(diphenylphosphino)-1,1′-binaphthalene. ^e3,5-Me₂BzOH was omitted, 150 °C. ^fdCype (6 mol%), dCype = bis-(dicyclohexylphosphino)ethane. A 13% yield of the ketol cycloadduct also was obtained.