C14 bond. Diene 2 could be formed from lactone 3 by an aldol
reaction with aldehyde 4 and subsequent oxidation. The spiroquaternary
center could be constructed by Claisen rearrangement
of allyl alcohol 5 obtained by aldol condensation between
bicyclic enone 6 and the corresponding glycolaldehyde
derivative. Further, bicyclic enone 6 could be accessed via the
Diels.Alder reaction of methylacrolein and diene 7.
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) (Scheme 2).5 1H NOE
spectroscopy determined the configuration of aldehyde 8,
which was reduced under the Huang.Minlon conditions6 and
subsequently treated with 2 N HCl to deliver enone 6 in 85%
overall yield.7 Aldol condensation between enone 6 and TBSprotected
glycolaldehyde resulted in a 34% yield. Hence, enone
6 was first converted to phosphonate 9 and 9Œ8 and then