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
作者:E. Demole、P. Enggist、Mlle C. Borer
DOI:10.1002/hlca.19710540712
日期:1971.11.1
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
室温下,(±)-神经甾醇(顺式/反式混合物)与N-溴琥珀酰亚胺在CCI 4中的离子反应,得到2-甲基-2-乙烯基-5-(2-溴-6-甲基庚-5-烯-2-基)-四氢呋喃(4),产率高。通过将可力丁回流到中间体烯丙基乙烯基醚8中,可以很容易地使该化合物脱氢溴化,该中间体立即经历[3,3]σ重排成2,5-二甲基-2-(4-甲基戊-3-烯基)-环庚-4-烯酮(11)。通过在室温下在硝基甲烷中用SnCl 4处理,依次将11环化为顺式-3,3,7,10-四甲基-2-氧杂-三环[5.5.0.0 1,4 ] dodec -9-ene(12),一种与倍半萜胡萝卜素密切相关的氧杂环丁烷。该氧杂环丁烷(12)在用路易斯酸(例如H 2 AICI或HAlCI 2)处理时发生立体定向环收缩,形成β-ac三烯(13)。最后,后者经BF 3催化的环化反应得到2,通过部分区域选择性加氢容易地获得2-表位-α-十六烯(20)