Mukaiyama aldimines

An exceptionally mild procedure for the cross-condensation of aldimines and enolsilanes has been described (eq. [67]) (80). This titanium tetrachloride-mediated reaction is predicated on the previous analogies provided by Mukaiyama for related aldol condensations (73a). Depending on aldimine structure and reaction time, either -lactams or their penultimate amino esters may be isolated from the reaction. The authors postulate that these reactions are proceeding via titanium enolates derived from ligand exchange by... 

Fig. 13). The cross-linked scandium-modified dendrimer was tested in a number of Lewis acid-catalyzed reactions, including Mukaiyama aldol additions to aldehydes and aldimines, Diels-Alder reactions, and Friedel-Crafts acylations. The dendritic catalyst was recovered by a simple filtration. The Mukaiyama aldol... 

Table 6.18 Thiourea-catalyzed Mukaiyama-Mannich reactions of aldimines.

Thiourea-Catalyzed Mukaiyama-Mannich Reactions of Aldimines [12] (p. 215)... 

New Au(III)-pyridine-2-carboxylate complexes were developed to catalyze the intramolecular reaction between furan and acetylene to form phenols <04AE(G)6545>. These pre-catalysts provide higher reaction conversion than AuClj. The Lewis acid catalyzed vinylogous Mukaiyama-Mannich addition of trimethylsilyloxyfuran to aldimines, that generates 6-amino-Y-butenolide intermediates, was applied to the synthesis of piperidines... 

Ishihara developed a highly efficient Mukaiyama aldol reaction between ketones and trimethylsilyl enolates catalysed by sodium phenoxide-phosphine oxides (46) as simple homogeneous Lewis-base catalysts (0.5-10 mol%) (Scheme 2.29). For a variety of aromatic ketones and aldimines, aldol and Mannich-type products with an a-quaternary carbon centre were obtained in good to excellent yields. Remarkably, a retro-aldol reaction was not observed. On a scale of up to 100 mmol, benzophenone and trimethylsilyl enolate gave the product in 97% yield (34.8 g) using 0.5 mol% of catalyst. 

The enantioselective vinylogous Mukaiyama—Michael addition of 2-silyloxyfurans to cyclic unsaturated oxo esters afforded a variety of compounds bearing a y-butenolide or y-lactone connected to a cycloalkane or cycloalkene moiety (13JOC2289). The reaction of siloxyfurans with aromatic aldimines could be catalyzed efficiently by silver(I) complexes of the Ar-BlNMOL-derived chiral monophosphine (13T8777). 

Less traditional Lewis acid catalysts have also been employed to mediate additions of silyl ketene thioacetals to imines and hy-drazones, including scandium(III) triflate and bismuth(III) triflate. In a significant recent advance, Mukaiyama and coworkers reported Lewis base catalyzed additions of the trimethylsilyl congener of the title reagent to iV-sulfonyl aldimines (eq 18). The reaction is tolerant of water and competent Lewis base activators include readily obtained salts such as lithium acetate and lithium benzamide. 

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