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The silver-catalysed multicomponent reaction between ethyl glyoxylate, 2,2-dimethoxyacetaldehyde, or phenylglyoxal as aldehyde components with a α-amino ester hydrochloride and a dipolarophile in the presence of triethylamine is described. This domino process takes place at room temperature by in situ liberation of the α-amino ester followed by the formation of the imino ester, which is the precursor of a metalloazomethine ylide. The cycloaddition of this species and the corresponding dipolarophile affords polysubstituted proline derivatives. Ethyl glyoxylate reacts with glycinate, alaninate, phenylalaninate and phenylglycinate at room temperature in the presence of representative dipolarophiles affording endo -2,5- cis -cycloadducts in good yields and high diastereoselection. In addition, 2,2-dimethoxyacetaldehyde is evaluated with the same amino esters and dipolarophiles, under the same mild conditions, generating the corresponding endo -2,5- cis -cycloadducts with higher diastereoselections than the obtained in the same reactions using ethyl glyoxylate. In the case of phenylglyoxal the corresponding 5-benzoyl- endo -2,5- cis cycloadducts are obtained in short reaction times and similar diasteroselection. [ABSTRACT FROM AUTHOR]

Abstract: Binap-AgSbF6 catalyzed 1,3-dipolar cycloadditions between azomethine ylides and electrophilic alkenes are described and compared with analogous transformations mediated by other Binap-silver(I) salt complexes. Maleimides and 1,2-bis(phenylsulfonyl)ethylene are suitable dipolarophiles for obtaining very good enantioselectivities, even better values are generated by a multicomponent version. There are some very interesting applications of the disulfonylated cycloadducts in the total synthesis of cis-2,5-disubstituted pyrrolidines, precursors of natural products, or valuable intermediates in the synthesis of antiviral compounds. [Copyright &y& Elsevier]

The kinetics of 1,3-dipolar cycloaddition involving azomethine ylides, generated from thermal 1,2-prototropy of the corresponding imino ester, employing differential scanning calorimetry (DSC), is surveyed. Glycine and phenylalanine derived imino esters have different behavior. The first one prefers reacting with itself at 75 °C, rather than with the dipolarophile. However, the α-substituted imino ester gives the cycloadduct at higher temperatures. Thermal dynamic analysis, by using 1H NMR spectroscopy, of the neat reaction mixture of the glycine derivative reveals the presence of signals corresponding to the dipole in small abundance. The non-isothermal and isothermal DSC curves of the cycloaddition of phenylalaninate and diisobutyl fumarate are obtained from freshly prepared samples. The application of known kinetic models and mathematical multiple non-linear regressions (NLR) allow the determintion and comparison of Ea, ln A, reaction orders, and reaction enthalpy values. Finally a rate equation for each different temperature studied can be established for this particular thermal cycloaddition. [ABSTRACT FROM AUTHOR]

An abstract of the article "Binap-Silver-Catalyzed Enantioselective Multicomponent 1,3-Dipolar Cycloaddition of Azomethines Ylides Derived from Ethyl Glyoxylate" by J. Mancebo-Aracil and colleagues is presented.

The application of AgSbF6 in the Binap-catalyzed enantioselective cycloaddition between azomethine ylides and alkenes is compared with previously reported analogous transformations mediated by AgClO4. [ABSTRACT FROM AUTHOR]