Cycloadditions with (E)- and (Z)-1-propenyl ethers

The tandem (4 + 2)/(3 + 2) cycloaddition of methyl (E,E)-7-nitro-2,6-dienoate with ethyl (E)- and (Z)-1-propenyl ethers involves the creation of three stereogenic centers at each of the cycloaddition stage. Hydrogenolysis of the cycloadducts yields alpha-hydroxy lactams with beta-configuration for the new methyl group. The study points to the influence of the exclusive endo preference of the alkoxy group during the (4 + 2) stage, which forces the alkyl beta-group to take up positions dictated by the dienophile geometry.