Abstract
According to the relevant literature, the Diels-Alder reaction of furan without a catalyst can last several weeks and shows a low yield due to the diene's low reactivity. The use of Lewis acid catalysts or high pressures is described as an effective method for improving the reaction yields. This paper describes our recent study on the use of niobium pentachloride as the catalyst in Diels-Alder reactions between furan and several reactive dienophiles, among which methyl acrylate showed good yields, especially at lower temperatures. Other dienophiles have shown lower yields because of problems such as byproduct formation and the high reversibility of the reaction.
Highlights
The Diels-Alder reaction of furan ring (1) with a reactive dienophile (2) provides 7-oxabicyclo[2.2.1] hept-5ene (3), an important intermediate in the synthesis of several natural products such as terpenes (4), prostaglandins (5), shikimic acid (6), and its analogues (Scheme 1).[1,2]Several researchers have described methods for synthesizing these cyclic intermediates
The niobium pentachloride activity as a catalyst was investigated in Diels-Alder reactions between furan (1) and several reactive dienophiles – methyl acrylate (2a), acrylonitrile (2b), dimethyl maleate (2c), and 2-chloroacrylonitrile (2d) – (Scheme 2) changing reaction parameters such as temperature, catalyst ratio, and reaction length
The Diels-Alder reaction is reversible, and due to the easy way in which cycloadditions with 1 undergo a reverse reaction, we started a study on the ideal reaction length using 10 mol% of the catalyst
Summary
The Diels-Alder reaction of furan ring (1) with a reactive dienophile (2) provides 7-oxabicyclo[2.2.1] hept-5ene (3), an important intermediate in the synthesis of several natural products such as terpenes (4), prostaglandins (5), shikimic acid (6), and its analogues (Scheme 1).[1,2]Several researchers have described methods for synthesizing these cyclic intermediates. This study used niobium pentachloride as the Lewis acid in synthesizing 7-oxabicyclo[2.2.1]hept-5-ene (3) derivatives through the Diels-Alder reaction between furan (1) and reactive dienophiles (2a-d) (Scheme 2) to evaluate the catalyst activity in the reaction yields and the selectivity of the products. The Diels-Alder reaction between furan (1) and several reactive dienophiles (2a-d).
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