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Synthesis based on cyclohexadienes. Part 25. Total synthesis of (+/-)-allo-cedrol (khusiol)

Sathya Shanker, P and Subba Rao, GSR (1998) Synthesis based on cyclohexadienes. Part 25. Total synthesis of (+/-)-allo-cedrol (khusiol). In: journal of The Chemical Society Perkin Transactions 1 (01). pp. 539-547.

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The first stereoselective total synthesis of (+/-)-allo-cedrol 20, an enantiomer of khusiol and a complex sesquiterpene having a novel tricyclo[,5)]undecane framework, is reported from 8-methoxytricyclo[,6)]dodec-6-en-9-one 6c. The methodology involves preparation of 9-methoxytricyclo[,6)]dodec-6-en-8-one 12 from 6c and its conversion through the compounds 8-benzyloxy-7,7-dimethyl-9-methoxytricyclo[,6)]dodec-5-ene 38, 7-benzyloxy-8-methoxy-2,6,6-trimethyltricyclo[,5)]undecane 48 into 8-methoxy-2,6,6-trimethyltricyclo[,5)]undecan-7-one 49. Wittig reaction of 49 affords the olefin 50 which has been smoothly rearranged into khusione 51. Metal-ammonia reduction of khusione under specific conditions affords (+/-)-allo-cedrol. Thus, bridgehead substitution of a methoxy group by a methyl group is the key reaction in this synthesis. In an alternative strategy, attempted conversion of 8-methoxy-2-methyltricyclo[,5)]undec-5-en-7-one 16 into khusione 37 results in an inseparable mixture of the isomers. A notable observation in this synthesis is the unusual formation of a gamma-alkylated product 27 during Woodward methylation of 16.

Item Type: Journal Article
Publication: journal of The Chemical Society Perkin Transactions 1
Publisher: Royal Society of Chemistry
Additional Information: Copyright of this article belongs to Royal Society of Chemistry.
Department/Centre: Division of Chemical Sciences > Organic Chemistry
Date Deposited: 17 Dec 2009 11:39
Last Modified: 19 Sep 2010 05:28
URI: http://eprints.iisc.ac.in/id/eprint/19387

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