Abstract
Graphene oxide (GO) catalysed multi component reaction of azomethine ylide driven 1,3 dipolar cycloaddition reaction in aqueous ethanolic solution is reported for the first time. This strategy has been applied for the synthesis of poly heterocyclic spiro-indenoquinoxaline pyrrolizidines and spiro-oxindoles pyrrolizidines with good to excellent yield along with excellent regio and diastereoselectivity. An ultra-low catalyst loading of 0.50 wt% was found to be efficient to catalyse the reaction.
Highlights
Development of carbon based heterogeneous catalysts in recent times has opened new vistas in the areas of green and sustainable chemistry.[1]
multicomponent reactions (MCR) associated with 1,3 dipolar cycloaddition reactions (1,3 DCR) of azomethine ylides has been largely explored in recent time for the synthesis of pyrrolizidine and substituted pyrrole core which represent a large class of alkaloids (Fig. 1).[14]
The reaction was performed at room temperature (RT) using ethanol as solvent, desired product was formed in very low yields even a er 24 h (Table 1, entry 1) without any catalyst (Scheme 1)
Summary
Development of carbon based heterogeneous catalysts in recent times has opened new vistas in the areas of green and sustainable chemistry.[1]. The emergence of multicomponent reactions (MCR) has provided chemists an effective means of synthesizing complex, multifunctional moieties by overcoming complex synthetic procedures They have proved to be efficient and robust in operation, improving areas like drug discovery and material sciences over last few decades.[12] Especially aqueous MCRs are promising strategies in the purview green chemistry.[13] MCR associated with 1,3 dipolar cycloaddition reactions (1,3 DCR) of azomethine ylides has been largely explored in recent time for the synthesis of pyrrolizidine and substituted pyrrole core which represent a large class of alkaloids (Fig. 1).[14] This strategy has enabled the chemists to concise the synthesis of spirooxindoles which are one of the widely occurring spiro alkaloids[15] along with a large synthetic analogue pool of spirooxindoles, with biological activities[16] as well as few other natural products.[17] it can be observed from the literature reports, many reactions suffer from longer reaction time, involves use of metal salts like silver or copper and volatile organic solvents.12a There are very few reports in the literature on aqueous 1,3 dipolar cycloaddition reactions involving azomethine ylides is reported.[18] We believe a robust, rapid, highly selective, green method for the synthesis of spiro molecules is of high value. To best of our knowledge, this is the rst report of graphene oxide (GO) catalysed azomethine ylide 1,3 dipolar cycloaddition reaction in aqueous medium
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