| Abstract
| - A novel, highly stereoselective synthesis of an azaspirocyclic core, which contains four stereogeniccarbons consistent with structures of natural halichlorine and pinnaic acid, is presented. LipasePS-catalyzed selective acylation, asymmetric methylation on the α-methylene of the bicyclic lactone,and an asymmetric Michael addition of the tertiary nitro cyclopentane were concisely used to conquerthe challenging problem of successfully constructing the C9 quarternary carbon center with completestereocontrol. The spiropiperidine ring was formed by reduction of the δ-nitroketone, intramolecularcondensation, and then highly stereoselective reduction of the cyclic nitrone with NaBH4. Thisspirocyclic core is a key intermediate in Danishefsky's synthesis of pinnaic acid and halichlorine.
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