Abstract
An asymmetric annulation reaction of γ-butenolides and cyclic 1-azadienes containing a 1,2-benzoisothiazole-1,1-dioxide motif has been studied, proceeding in a tandem Michael addition-aza-Michael addition sequence. Endo-type cycloadducts bearing fused tetracyclic skeletons were isolated in fair yields and with high enantioselectivity (up to >99% ee) under the catalysis of modified cinchona alkaloid (DHQD)2PHAL. Besides, exo-type diastereomers could be produced using β-isocupreidine (β-ICD) as the catalyst, though with moderate enantioselectivity.
Highlights
Introduction γButenolides represent an important class of heterocycles, which widely exist in a large number of natural products and pharmaceutically useful molecules [1,2]
With the optimized conditions in hand, we explored a variety of cyclic 1-azadienes 2 and γ-butenolides 3 under the catalysis of (DHQD)2PHAL 1g in PhCF3 at 20 °C
We have investigated the asymmetric and β,γ-regioselective [4+2] annulation reactions of γ-butenolides and cyclic 1-azadienes containing a 1,2-benzoisothiazole-1,1-dioxide motif
Summary
Introduction γButenolides represent an important class of heterocycles, which widely exist in a large number of natural products and pharmaceutically useful molecules [1,2]. Molecules 2015, 20 vinylogous addition reactions, to the best of our knowledge, no examples have been reported to utilize the γ-butenolides as the reactants towards tandem reactions in consideration of the potential reactivity of both γ- and β-positions [14]. Our group reported a direct asymmetric allylic alkylation of γ-butenolides with MBH carbonates to access γ,γ-disubstituted butenolides that could allow sequential aza-Michael addition to deliver interesting bicyclic piperidine derivatives [15]. These results inspired us to explore domino or tandem Michael addition-aza-Michael addition to construct a variety of polycyclic skeletons.
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