An expedient synthesis of spiroketals: model studies for the calyculin C16–C25 fragment
نویسندگان
چکیده
A new short strategy to prepare the spiroketal fragment of calyculins is presented. A novel Seyferth–Gilbert type homologation of hindered lactols to the corresponding alkynes has been achieved for the first time. The spirocyclization was achieved efficiently via a DIHMA (double intramolecular hetero-Michael addition) process of this hindered ynone. The spirocyclization rate is not dependent on the stereochemistry of the alkoxy substituent in the oxolane ring. q 2004 Elsevier Ltd. All rights reserved.
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