| Abstrakt: |
We have studied the cyclization of (4Z)-2,2,5,8,8-pentamethyl-4-nonene-3,7-dione (3E)-oxime (2). We have previously claimed the formation of a stable 3,5,5-trisubstituted 3-isoxazolidinol and of a bridged bicycle 4,5-dihydro-2,5-methano-1,4,3-dioxazepine in the reaction of 2 with hydrochloric acid in anhydrous diethyl ether. We report in this article that the above compounds are actually 3,3-dimethyl-1-(5'-tert-butyl-5'-hydroxy-3'-methylisoxazolidin-3'-yl)butan-2-one (5) and 1,3-di-tert-butyl-5-methyl-2,7-dioxa-6-azabicyclo[3.2.1]oct-3-ene (6). The formation of these products involves the splitting of hydroxylamine in 2 and its re-addition as an O-nucleophile under acidic reaction conditions. Surprisingly, 5 provided the 2-isoxazoline derivative 3 on heating or on standing in CDCl3/TFA solution at room temperature. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) |
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