Stanislawski PC, Willis AC, Banwell MG. gem-Dihalocyclopropanes as Building Blocks in Natural-Product Synthesis: Enantioselective Total Syntheses ofent-Erythramine and 3-epi-Erythramine.
Chem Asian J 2007;
2:1127-36. [PMID:
17694511 DOI:
10.1002/asia.200700155]
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Abstract
ent-Erythramine ((-)-1), the enantiomer of the alkaloid erythramine, was prepared in 15 steps from known compounds. The first of three pivotal bond-forming steps in the synthesis was a Suzuki-Miyaura cross-coupling reaction of the starting materials to give a bis-silyl ether. The second involved silver(I)-induced electrocyclic ring opening of the gem-dichlorocyclopropane formed in the next step and trapping of the ensuing pi-allyl cation by the tethered nitrogen atom to give, following cleavage of the allyloxycarbonyl protecting group, an approximately 5:6 mixture of the chromatographically separable diastereoisomeric spirocyclic products. In the third critical bond-forming reaction, the iodide formed from one of the diastereoisomers underwent a radical-addition/elimination reaction sequence that led to (-)-1 in 89 % yield. The application of the same sequence of transformations to the other diastereoisomer afforded 3-epi-(+)-erythramine (3-epi-(+)-1).
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