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[摘要]：Cis-4-(1-Chloro-1-methylethyl)-1-(w-hydroxyalkyl)azetidin-2-ones (I, R = Ph, Bn, Me; n = 1, 2) were diastereoselectively transformed into novel trans-1-aza-4-oxabicyclo[3.3.0]octan-8-ones II (n = 1) and trans-1-aza-5-oxabicyclo[4.3.0]nonan-9-ones II (n = 2) upon treatment with 1 equiv of AgBF4 and pyridine in toluene via intramol. nucleophilic trapping of N-acyliminium intermediates by the hydroxyl moiety. Addnl., the corresponding aza-analogs of the aforementioned bicyclic g-lactams (i.e., trans-1,4-diazabicyclo[3.3.0]octan-8-ones and trans-1,5-diazabicyclo[4.3.0]nonan-9-ones) were prepd. in a convenient way starting from cis-4-(1-chloro-1-methylethyl)-1-{w-[(tert-butoxycarbonyl)amino]alkyl}aze tidin-2-ones (III) applying the same reaction conditions. The intermediate N-acyliminium ions were formed by ring expansion of the starting b-lactams through generation of a transient silver(I)-induced carbenium ion. |
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