Abstract
We provide a comprehensive account of the 1,3-dipolar cycloaddition reactions of azomethine ylides with carbonyl dipolarophiles. Many different azomethine ylides have been studied, including stabilized and non-stabilized ylides. Of the carbonyl dipolarophiles, aldehydes including formaldehyde are the most studied, although there are now examples of cycloadditions with ketones, ketenes and carboxyl systems, in particular isatoic anhydrides and phthalic anhydrides. Intramolecular cycloadditions with esters can also occur under certain circumstances. The oxazolidine cycloadducts undergo a range of reactions triggered by the ring-opening of the oxazolidine ring system.
Highlights
The versatile and convergent nature of the 1,3-dipolar cycloaddition reaction has led to its development as a powerful method for the synthesis of five-membered heterocycles [1,2,3,4,5,6,7]
Intramolecular cycloaddition of the non-stabilized azomethine ylide generated from the Schemcoend2e6n. sIantitoranmofoαle-acmulianrocayccidlosawdidthitaioldnehoyfdtehsebneoarnin-sgtaabtieltihzeerdedazalodmeheytdhein. e ylide generated from the condensation of α-amino acids with aldehydes bearing a tethered aldehyde. Further examples of this type of intramolecular 1,3-dipolar cycloaddition process include the reaction of intermediate azomethine ylides derived from dialdehyde 110 and (a) sarcosine (47), which resulted in the stereoselective formation of cis-fused oxazolidine-grafted macrocycles 111; (b) thiazolidine-4-carboxylic acid (62) to form tetrahydrooxazolothiazoles 112; and (c) L-proline (50) to give hMeoxleacuhleys d20r1o6,p2y1,r9r3o5looxazole grafted macrocycles 113 (Scheme 27) [101]
Harwood and co-workers have reported the diastereoselective synthesis of bicyclic oxazolidines via 1,3-dipolar cycloaddition reactions of azomethine ylides derived from the condensation of 5-(S)-phenylmorpholine-2-one (139) with aldehydes 2, and their subsequent trapping by the carbonyl bond of a second equivalent of the aldehyde 2
Summary
The versatile and convergent nature of the 1,3-dipolar cycloaddition reaction has led to its development as a powerful method for the synthesis of five-membered heterocycles [1,2,3,4,5,6,7]. The most frequent type of 1,3-dipolar cycloaddition reaction of azomethine ylides is that with alkenyl or alkynyl dipolarophiles substituted with electron-withdrawing groups, providing access to pyrrolidine-containing molecules of biological [18,22,23,24,25,26] or materials science interest [27,28,29,30,31]. There has been a resurgence of interest in reactions with carbonyl compounds, including aldehydes 2, ketones 3, ketenes 4 or carboxylates 5 as the heterodipolarophile, which yield oxazolidine derivatives 6 (Scheme 1). This recent interest has been due to the recognition that anhydrides.
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