Total Synthesis of (+)-Azaspiracid-1. An Exhibition of the Intricacies of Complex Molecule Synthesis
摘要:
The synthesis of the marine neurotoxin azaspiracid-1 has been accomplished. The individual fragments were synthesized by catalytic enantioselective processes: A hetero-Diels-Alder reaction to afford the E- and HI-ring fragments, a carbonyl-ene reaction to furnish the CD-ring fragment, and a Mukaiyama aldol reaction to deliver the FG-ring fragment. The subsequent fragment couplings were accomplished by aldol and sulfone anion methodologies. All ketalization events to form the nonacyclic target were accomplished under equilibrating conditions utilizing the imbedded configurations of the molecule to adopt one favored conformation. A final fragment coupling of the anomeric EFGHI-sulfone anion to the ABCD-aldehyde completed the convergent synthesis of (+)-azaspiracid-1.
Cyclopentannulation of enones with organocuprate reagents containing an acetal or an orthoester function
摘要:
1,1-Dimethyl-3-(phenyldio)-propane 4 was deprotonated with t-BuLi, then converted to the corresponding organocuprate reagent which, in the presence of HMPA and TMSCl was added to a variety of enones to give the corresponding silylenol ethers 7. These were cyclised without purification upon acidic conditions to give the cyclopentannulation products 9. A similar result was obtained with the corresponding orthoester reagent 6. This cyclopentannulation sequence is applicable to a wide variety of enones except for those bearing substituents near the reacting centre. (C) 2002 Published by Elsevier Science Ltd.