1-Azaspiro Annelation: A Synthetic Approach to Naturally Occurring Heterocyclic Spiranes

Abstract
The synthesis of 1-azaspiro[4, 4]nonans, -[4, 5]decanes and -[5, 5]undecanes has attracted considerable attention in recent years with special interest in natural products such as histrionacotoxin,1 serratinine2 and harringtonine.3 We have been investigating several synthetic approaches to these systems in hopes of developing one general approach to all such compounds. We were particularly interested in simplicity and chose to utilize a preformed, readily accessible, carbocyclic ring to which the spiro-heterocyclic or nitrogen containing ring would be attached. Illustrative of these general considerations was the approach shown in Scheme I.

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