Applications synth�tiques de la cyclisation d'alcools tertiaires ?-�thyl�niques en ?-bromot�trahydrofurannes sous l'action du N-bromosuccinimide. II. Cyclisation du (�)-n�rolidol en dim�thyl-2,5-(m�thyl-4-pent�ne-3-yl)-2-cyclohept�ne-4-one, t�tram�thyl-3, 3, 7, 10-oxa-2-tricyclo[5.5.0.01,4]-dod�c�ne-9, ?-acoratri�ne, c�dradi�ne-2,8,�pi-2-?-c�dr�ne et ?-c�dr�ne

Autor: P. Enggist, E. Demole, Mlle C. Borer
Rok vydání: 1971
Předmět:
Zdroj: Helvetica Chimica Acta. 54:1845-1864
ISSN: 1522-2675
0018-019X
DOI: 10.1002/hlca.19710540712
Popis: The ionic reaction of (±)-nerolidol (cis/trans mixture) with N-bromosuccinimide in CCI4 at room temperature afforded 2-methyl-2-vinyl-5-(2-bromo-6-methyl-hept-5-en-2-yl)-tetrahydrofuran (4) in high yield. This compound was readily dehydrobrominated by refluxing collidine to the intermediate allyl vinyl ether 8, which immediately undergoes [3,3]-sigmatropic rearrangement to 2, 5-dimethyl-2-(4-methylpent-3-enyl)-cyclohept-4-enone (11). By treatment with SnCI4 in nitromethane at room temperature 11 was in turn cyclised to cis-3, 3, 7, 10-tetramethyl-2-oxa-tricyclo[5.5.0.01,4]dodec-9-ene (12), an oxetane closely related to the sesquiterpene carotol. This oxetane (12) underwent a stereospecific ring contraction when treated by Lewis acids such as H2AICI or HAlCI2, to form the β-acoratriene (13).Finally, the BF3-catalysed cycli- sation of the latter afforded 2,8-cedradiene (19) from which 2-epi-α-cedrene (20) was easily obtained by partial, regio-selective hydrogenation. α-Cedrene (22) itself, together with its epimer 20, resulted from the Wolff-Kishner reduction of the 2-epi-α-cedren-3-one (21), prepared by selective hydroboration/oxidation of 19. A transformation of nerolidol to α-cedrene was thus achieved by a unique stepwise cyclisation process.
Databáze: OpenAIRE
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