Imine ester

Synthetic work commenced with evaluation of an azomethine ylide dipole for the proposed intramolecular dipolar cycloaddition. A number of methods exist for the preparation of azomethine ylides, including, inter alia, transformations based on fluoride-mediated desilylation of a-silyliminium species, electrocyclic ring opening of aziridines, and tautomerization of a-amino acid ester imines [37]. In particular, the fluoride-mediated desilylation of a-silyliminium species, first reported by Vedejs in 1979 [38], is among the most widely used methods for the generation of non-stabilized azomethine ylides (Scheme 1.6). 

The preorganisation approach (b) involves formation of strong reversible covalent arrangements (boronate esters, imines, ketals) of the monomers... 

Keeping in view the biological and synthetic importance of the (3-lactams and the potential of solvent-free microwave chemistry, Kidwai et al. [148] prepared (3-lactams via an ester-imine based synthesis under solvent-free microwave irradiation. The //Y/n.v-4-aminocyclohexanol (128) was condensed with different aromatic aldehyde to give the respective Schiff base. The Schiff-base was then reacted with ethyl a-mercapto/a-cyano acetate, in the presence of basic alumina, to afford the required 3-mercapto/cyano (3-lactams respectively, outlined in Scheme 41. 

A possible mechanism is intermolecular proton transfer from one molecule of the starting ester-imine to another to give a 1,3-dipole, which then cycloadds to the acetylene. 

Alkylations of acyclic enolates containing a collection of chiral auxiliary groups have been used successfully for the asymmetric synthesis of carboxylic acids. The chiral, nonracemic substrates that have been used include amides, imides, esters, imine derivatives of glycinates and acyl derivatives of chiral transition metals. In these systems either extraannular or chelate-enforced intraannular chirality transfer may control the sense of the alkylation step. 

Hart and his co-workers have extended the utility of the ester-imine procedure in a different way, by showing that... 

The 1,3-dipolar cycloaddition reaction of azomethine ylides with thioketones has been used to prepare 1,3-thiazoIidines. The metallated azomethine ylides 67 were generated in situ by treating a-amino acid ester imines 66 with lithium bromide and DBU. The ylides were then treated with highly reactive thioketones such as thiobenzophenone or fluorene-9-thione, to afford 1,3-thiazolidine derivatives 68 (main isomer) and 69 (minor isomer) in good yield and in diastereoisomeric ratios of between 2 1 and 4 1 <01H(55)691>. 

TBAF-assisted Trifluoromethylation, Perfluoroalkylation, and Polyfluoroalkoxylation. TBAF combines with TMSCF3 to form nucleophilic trifluoromethyl anion equivalents. The precise structure of this nucleophile is unknown, although it is likely that a pentacoordinate silicon intermediate is involved. The TBAF/TMSCF3 combination leads to smooth trifluoromethylation of aldehydes,ketones, esters, imines, nitroso compounds, a-ketoesters, Q -ketoamides (eq and... 

Condensation of ester enolates with heterocumulenes [23b, c] represents a case of ester-imine coupling wherein the stabilized primary addition product... 

Diazoalkanes," azides, " partial oxiranes, oxazolidinone, " aziri-dines, trimethylsilyhnethyltriflate salts (TfO TMSM ), and a-aminoac-id ester imines form pentaatomic rings through reactive intermediate ylides. Species like thiocarbonyl S-ylides, " thiocarbonyl S-imides, thiocar-bonyl S-sulfides (thiosulfines), and thiocarbonyl S-oxides (sulfines) containing a three atomic system as central unit with the sulfur atom in the middle position are known as sulfur centred 1,3-dipoles. Oxiranes react opening the ring by L.A. Thiosulfines, " reactive intermediates in the formation of 1,2,4-trithiolanes, are not isolable species since they decompose to thione and sulfur. 

North and coworkers have investigated application of Cu(II)/salen complex (405) and derivatives to enantioselective alkylation of alanine methyl ester imine (403) (Scheme 17.91) [128]. Numerous variations on the aryl rings of the salen ligand... 

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