INTRAMOLECULAR CYCLIZATIONS OF CYCLODECENES

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Many natural products of biological interest contain as part of their structure a hydroazulene nucleus that is substituted at one of the bridgehead carbons with a hydroxyl group. Examples include the tumor- promoting phorbol esters (10) and the neurotoxic grayanotoxins. A two-step methodology for generating bicyclo[5.3.0]-decan-1-ols is described herein that should be a general solution to the synthesis of such structures. Oxy-Cope rearrangement of a divinylcyclohexanol followed by intramolecular allylsilane condensation of the resultant cyclodec-5-enone leads to the desired hydroazulenol. The overall result of this sequence is cyclopentane annulation with concommitant one-carbon ring expansion of a cyclohexane ring to give the hydroazulene nucleus. Two different variations of this sequence that should allow for the preparation of either the cis or trans ring fusion of the hydroazulene will be examined. Several other strategies, including one that involves transannular radical cyclization of an oxygen-stabilized radical center and another that makes use of a variant of an anion accelerated Cope rearrangement, will also be investigated.