A novel enantiopure tricyclic β-lactam via stereoselective intramolecular nitrilimine cycloaddition |
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Authors: | Paola Del Buttero Giorgio Molteni Tullio Pilati |
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Institution: | 1. Università degli Studi di Milano, Dipartimento di Chimica Organica e Industriale, via Golgi 19, 20133 Milano, Italy;2. Consiglio Nazionale delle Ricerche, Istituto di Scienze e Tecnologie Molecolari, via Golgi 19, 20133 Milano, Italy |
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Abstract: | Starting from the Staudinger 2+2] cycloaddition between the 1-azadiene 1 and acetoxyacetylketene, generated in situ from acetoxyacetyl chloride, we developed a seven-step synthesis of the novel azeto3′,4′:2,3]pyrano4,5-c]pyrazole skeleton 9 in both racemic and enantiopure forms. Silver carbonate treatment of the functionalised hydrazonoyl chloride 7 promoted in situ generation of the corresponding nitrilimine 8, which underwent a clean, stereoselective cycloaddition to the target tricyclic β-lactam 9. The key step of the synthetic pathway leading to enantiopure 9 was the production of the enantiopure azetidinone (3R,4S)-3 by enzymatic resolution with Amano Lypase PS of the racemic precursor (3S1,4R1)-2. |
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