Abstract
A mild, efficient, and environmentally benign protocol for the synthesis of tetrahydrobenzo[b]pyran derivatives in the presence of readily accessible, biodegradable, and choline hydroxide based ionic liquid as catalyst has been established. The key features of the reported methodology include good to excellent yields of desired products, simple work-up procedure and good recyclability of catalysts, which may be a practical alternative to the existing conventional processes for the preparation of 4-H pyrans to cater to the requirements of academia as well as industry.
Highlights
As an important class of oxygen-containing heterocycles, tetrahydrobenzo[b]pyrans are widely employed as potential biodegradable agrochemicals [1], photoactive materials [2], cosmetics and pigments [3]
New DBU derived ILs were found to be less suitable as catalysts for the preparation of the pyran product while they exhibited excellent catalytic activities for aza-Michael addition [48,49,50] and Knoevenagel condensation [48,49,50,51,52,53,54,55,56] (Table 1, entries 3 and 4)
[bmim]OH, a basic ionic liquid widely used in organic catalysis, gave slightly lower yield (86%)
Summary
As an important class of oxygen-containing heterocycles, tetrahydrobenzo[b]pyrans are widely employed as potential biodegradable agrochemicals [1], photoactive materials [2], cosmetics and pigments [3]. Because of the inherent reactivity of the pyran ring, 4-H pyrans are versatile synthons, which can be converted into pyridine compounds as pharmacologically important calcium. Tetrahedronhydro[b]pyran compounds themselves have a broad spectrum of biological properties [6,7], such as spasmolytic, anticancer, diuretic, anticoagulant, and antiancaphylactia activities [8,9]. They can be used as cognitive enhancers for the treatment of neurodegenerative disease, for example, Parkinson’s disease, Huntington’s disease, Alzheimer’s disease, amyotrophic lateral sclerosis, AIDS associated dementia and Down syndrome and for the treatment of schizophrenia and myoclonus [10]. Due to the versatile utilization of the pyran derivatives in the field of organic synthesis as well as in medicinal chemistry, many researchers have been encouraged to develop highly efficient procedures for the preparation of these kinds of compounds
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