An expedient formal total synthesis of (-)-diazonamide A via a powerful, stereoselective O-aryl to C-aryl migration to form the C10 quaternary center.
During the course of studies on the synthesis of diazonamide A 1, an unusual O-aryl into C-aryl rearrangement was discovered that allows partial control of the absolute stereochemistry of the C-10 quaternary stereogenic center. Treatment of 30 with TBAF/THF gave the O-tyrosine ethers 31 and 32 (1:1), which on heating each separately in chloroform at reflux rearranged to 33 and 34 in ratios of 84:16 and 56:44, respectively. This corresponds to a 70% yield of the correct C-10 stereoisomer 33 and a 30% yield of the wrong C-10 stereoisomer 34. Attempts to convert 34 into 33 by ipso-protonation and equilibration were unsuccessful. Confirmation of the stereochemical outcome of the rearrangement was obtained by converting 33 into 37, an advanced intermediate in the first synthesis of diazonamide A by Nicolaou et al. It was also found that the success of the above rearrangement is sensitive to the protecting group on both the tryptophan nitrogen atom and the tyrosine nitrogen atom.
Cheung
Chi-Ming
CM
Department of Chemistry and Biochemistry, University of Texas at Austin, 1 University Station A5300, Austin, Texas 78712-1167, USA.
Goldberg
Frederick W
FW
Magnus
Philip
P
Russell
Claire J
CJ
Turnbull
Rachel
R
Lynch
Vince
V
D000818:Animals; D006576:Heterocyclic Compounds, 4 or More Rings / Q000138:chemical synthesis* / Q000737:chemistry; D010080:Oxazoles / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism; D014443:Tyrosine / Q000031:analogs & derivatives / Q000145:classification; D014561:Urochordata / Q000737:chemistry
D006576:Heterocyclic Compounds, 4 or More Rings; D010080:Oxazoles; C408862:diazonamide A; D014443:Tyrosine