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A concise approach to the core structures of pinnaic acid and halichlorine
Sung-Hyun Yang1, G R Clark, Vittorio Caprio
1Department of Chemistry, The University of Auckland, 23 Symonds Street, Auckland, New Zealand.
Abstract:
An efficient and flexible synthetic approach to the core structures of pinnaic acid and halichlorine is described using spirocyclic nitrone 4 as a key intermediate. 1,3-Dipolar cycloaddition of 4 with dipolarophile 8 provides access to the azaspirocyclic core of pinnaic acid 5 while the spiroquinolizidine core of halichlorine 6 has been synthesised via cycloaddition of 4 with dipolarophile 29. Nitrone 4 is accessed by oxidative ring opening of isoxazolidine 9. The utility of this synthetic strategy in the synthesis of C5 substituted analogues of pinnaic acid is also demonstrated.
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