Radical cyclisation studies of chiral α-acylamino radicals : a model study towards Tacaman indole alkaloid synthesis
Master Thesis
1996
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University of Cape Town
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Abstract
he radical cyclisation of chiral 4,5-substituted N-acyl-2-aza-6-heptenyl radicals, derived from D-ribose, has been undertaken as a model stuay towards Tacaman indole alkaloid synthesis. The radical cyclisations were conducted using tributyltin hydride/AIBN in refluxing benzene. The α-acylamino radicals added to double bonds which were activated by an ethoxycarbonyl substituent. No reduction of the radicals by the tributyltin hydride was observed. Those radicals incorporating an isopropylidene ketal at the 4 and 5 positions as chiral auxiliary showed excellent regio- and stereoselectivity. Out of a possible 4 diastereomers, only two were obtained in a 2:8 ratio. It was established that the isopropylidene ketal directed the cyclisation stereoselectively and that no stereoselectivity was observed in the absence of the chiral auxiliary.
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Includes bibliographical references.
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Reference:
Clauss, R. 1996. Radical cyclisation studies of chiral α-acylamino radicals : a model study towards Tacaman indole alkaloid synthesis. University of Cape Town.