Synthetic Versatility of N-(Silylmethyl)imines: Water-Induced Generation of N-Protonated Azomethine Ylides of Nonstabilized Type and Fluoride-Induced Generation of 2-Azaallyl Anions

Abstract

N-(Silylmethyl)imines generate N-protonated azomethine ylides of nonstabilized type when treated with water in HMPA, which undergo stereospecific and regioselective cycloadditions with electron-poor olefins affording N-unsubstituted pyrrolidines. On the other hand, fluoride-induced desilylation of the imines leads to 2-azaallyl anions which are found to be synthetic equivalents of aminomethyl anion in the Michael additions with electron-poor olefins and nucleophilic additions with carbonyl compounds.

Three‐component 1,3‐dipolar cycloaddition reactions in synthesis of spiro[pyrrolidine‐2,3′‐oxindoline] derivatives

“…The designation of regio-and stereospecificity of the reaction is based on the multiplicity and coupling constant of 4-H in the NMR spectra of the cycloadducts 9a-i (Table 1). To determine the scope and synthetic potential of these multicomponent reactions, which tolerate wide variations in the dipolarophile component, we have utilized trapping of azoethine ylides of type 4 or 5 with arylidenemalononitrile derivatives (10). When a mixture of isatin, phenylalanine, and the benzylidenemalononitrile derivative (10a) was heated (reflux temperature) in aqueous ethanol for 5 h, a single cycloadduct (11a) was obtained in 70% yield.…”

“…The synthesis of such ring systems via multicomponent reactions, involving trapping of azomethine ylides by different dipolarophiles, have attracted the attention of several research groups, since three or more building blocks can be combined in one step to yield complex organic compounds [7]. In the last decade, several methods have been developed for the generation of azomethine ylides involving oxazolines [8], desilylation of N-(silylmethyl)imines [9] and related precursors [10], 1,2-prototropy in activated imines [11] and related metal-ion-catalyzed processes [12], and dehydrogenation of tertiary amines [13]. Also, the reactions of carbonyl compounds with primary and secondary, acyclic and cyclic, ␣-amino acids, with concomitant decarboxylation, have been reported to give azomethine ylides via an intermediate oxazolidin-5-one [14][15][16].…”

Perspectives on Intermolecular Azomethine Ylide [3+2] Cycloadditions with Non-Electrophilic Olefins

“…Tsuge introduced Nsilylmethylimines as viable sources of these intermediates. 30 However, the transmetallation process developed by Pearson using alkyltin-functionalized imines proved to be significantly more general (Scheme 3,c). 31 This way, the 2-aza-allyl anion chemistry could be extended to aliphatic and heterofunctionalized imines.…”

Cycloadditions of Nonstabilized2-Azaallyllithiums (2-Azaallyl Anions) and Azomethine Ylides withAlkenes: [3+2] Approaches to Pyrrolidinesand Application to Alkaloid Total Synthesis

“…3 It was not until the 1970s that Thomas Kauffmann and co-workers at the University of Münster pioneered the cycloaddition reactions of such anions in the form of their lithium salts (i.e., 2-azaallyllithiums). Tsuge and Kanemasa 5 have generated the 1-phenyl-2azaallyl anion 9 by desilylation of the (2-azaallyl)silane 8 and used it in cycloadditions with stilbenes and styrene (Scheme 3), thus extending Kauffmann's work to monoaryl semistabilized 2-azaallyl anions. Imines with enolizable hydrogens were found to be unsuitable for this method because they form 1-azaallyl anions upon treatment with base.…”