The synthesis began with diene 7, which was prepared in
three steps from 2-cyclohexenone on a multigram scale
according to a modified protocol.4 A Diels−Alder reaction
between diene 7 and methylacrolein proceeded smoothly at 40
°C and afforded aldehyde 8 in 89% yield with excellent regioand
diastereoselectivity (d.r. 12.5:1)