There has been a recent eruption in the number of known marine sesterterpenoids which have been isolated from Pacific Rim marine organisms. These compounds have novel and unusual structures that exhibit incredibly potent and varied bioactivities. This review details the isolation, biological testing and prospects for this exciting new family with discussion of their potential biogenetic origins.
2-Bromo-1,3-butadienes
are demonstrated to be effective substrates
for tandem Diels–Alder/transition metal cross-coupling reaction
sequences. Intermolecular cycloaddition of a 2-bromo-1,3-diene with
activated dienophiles proceeded under Lewis acid catalysis in generally
high yields with good to excellent endo diastereoselectivity.
The resulting vinyl bromide cycloadducts underwent subsequent Stille
and Suzuki cross-couplings under standard conditions in good yields.
Both the Diels–Alder and cross-coupling steps were highly tolerant
of a range of functionalities and protecting groups. The use of the
bromine substituent as both a cycloaddition directing group and cross-coupling
nucleofuge avoids extra steps required to install and remove the more
commonly used silyl enol ethers and enol sulfonates for each transformation
and gives full control of the alkene regiochemistry throughout the
reaction sequence. The 2-bromo-1,3-dienes were conveniently prepared
in three steps from readily available aldehydes and established as
hydrolytically stable and practical synthetic intermediates.
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