Total Synthesis Highlights
Total Synthesis Highlights
Total Synthesis Highlights
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This concise synthesis of the dolabellane 3 showcases the power of the catalytic enantioselective<br />
methods for the construction of both ternary and quaternary, including cyclic quaternary, centers<br />
that Professor Hoveyda has developed. Clearly, asymmetric transformation of inexpensive<br />
prochiral ring precursors such as 1 and 4 will make advanced, high ee intermediates such as 2 and<br />
5 much more readily available than they have been in the past.<br />
26. The Zakarian <strong>Synthesis</strong> of (+)-Pinnatoxin A<br />
(+)-Pinnatoxin A (3), isolated from the shellfish Pinna muricata, is thought to be a calcium<br />
channel activator. A key transformation in the synthesis of 3 reported (J. Am. Chem. Soc. 2008,<br />
130, 3774.) by Armen Zakarian, now at the University of California, Santa Barbara, was the<br />
diastereoselective Claisen rearrangement of 1 to 2.<br />
The alcohol portion of ester 1 was derived from the aldehyde 4, prepared from D-ribose. The<br />
absolute configuration of the secondary allylic alcohol was established by chiral amino alcohol<br />
catalyzed addition of diethyl zinc to the unsaturated aldehyde 5.<br />
The acid portion of the ester 1 was prepared from (S)-citronellic acid, by way of the Evans imide 7.<br />
Methylation proceeded with high diasterocontrol, to give 8. Functional group manipulation<br />
provided the imide 9. Alkylation then led to 10, again with high diastereocontrol. In each case,<br />
care had to be taken in the further processing of the α-chiral acyl oxazolidinones. Direct NaBH 4