Enolates analogues

All prepared magnesium enolates 17 are stable in refluxing diethyl ether. Deuteriation, and reactions with various electrophiles confirm their structure (see section HI). It is noteworthy that the lithiated carbanion-enolate analogue, directly obtained by deprotonation of an a-ketoester 18 with lithiated bases (LDA, for example), is not stable and immediately degrades in the medium, whatever the temperature. Comparatively, the magnesium chelate 17 shows a higher stability, which allows its preparation and synthetic applications. 

For example, the chelated magnesium enolate of a /3-diketone or a /3-ketoester 34 (formed via 33) can be easily prepared using (MeO)2Mg/MeOH as a base. It is stable in a refluxing solution of the reagent, in contrast with the sodium enolate analogue, which is unstable in these conditions. 

Thus, the methanolysis of the lactone 35 by MeONa or (MeO)2Mg produces initially the triketoester 36, which is subsequently deacylated in situ to give after hydrolysis the diketone ester 38. The yield of 38 is considerably better with (MeO)2Mg, as the result of the formation in the reaction medium of a chelated bis-enolate 37 which protects 38 from degradation. Extensive degradation is observed with the sodium enolate analogue of 37 which is unstable in these conditions (equation 56). ... 

It should be noted that the reaction of boron and lithium enolates analogues of 50 with ClP(0)(0Et)2 are unsuccessful. 

H. E. Zimmerman, Kinetic Protonation of Ends, Enolates, Analogues. The Stereochemistry of Ketoni-sation, dcc. Chem. Res. 1987, 20, 263. 

H. E. Zimmerman, Kinetic protonation of ends, enolates, analogues The stereochemistry of ketonisation, Acc. Chem. Res 1987, 20,263. 

Figure 6.40. Conversion of enolized analogue of the mtural aromatase substrate to the corresponding aromatized compound is catalyzed by a model peroxo ferric porphyrin complex.

The 11,12-carbonate of erythromycin (32) is an older cycHc ester which had greater stabdity and antibiotic activity by diminishing formation of intramolecular enol ether (27) (136,137). A later analogue, the ll-A/-12-0-cychc carbamate of... 

Examples of the remaining potential 3,4-dihydroxy heterocycles are presently restricted to furan and thiophene. Although the parent 3,4-dihydroxyfuran apparently exists as the dioxo tautomer (86), derivatives bearing 2-alkyl or 2,5-dialkyl substituents prefer the keto-enol structure (87) (71T3839, 73HCA1882). The thiophene analogues also prefer the tautomeric structure (87), except in the case of the 2,5-diethoxycarbonyl derivative which has the fully aromatic structure (88) (71T3839). 

There are few examples of formation of simple azetidines from [2 + 2] fragments, although this type of approach is important for certain azetidine derivatives, e.g. azetidin-2-ones (see Section 5.09.3). Nitrogen analogues of the Paterno-Buchi route to oxetanes are rare an example involves the photoaddition of 3-ethoxyisoindolone (37) to the enol ether (38) (75JA7288, 72CC1144). 

The term enamitie was first introduced by Wittig and Blumenthal (7) as the nitrogen analogue of the term enol. ... 

Ojima, 1., Habus, 1., Zhao, M. (1991) Efficient and Practical Asymmetric Synthesis ofthe Taxol C-13 Side Chain, N-Benzoyl-(2R,3S)-3-phenylisoserine, and its Analogues via Chiral 3-Hydroxy-4-aryl-b-lactams Through Chiral Ester Enolate-Imine Cyclocondensation. Journal of Organic Chemistry, 56, 1681-1683. 

Bromination rates of aliphatic enol ethers have been included in the interactive treatment of alkenes GRIC=CR R, with G being a conjugated group most of them fit the multiparameter equation (41) satisfactorily. A more detailed analysis of reactivity-selectivity effects in the reaction of 1-ethoxyethylene [22] and its a- and / -methyl analogues [23] and [24] has been carried out,... 

No data are available for compounds with C=Se and C=Te bonds and their equilibria with the seleno- and telluro-enol tautomer. For simple selenoacetone, its tautomer, and telluro-analogues, quantum mechanical calculations have been carried out using different methods.5 These calculations have shown that on passing from O to Te, the energy difference between the tautomeric forms is reduced, a trend that parallels the calculated C=E bond energies, which decrease from O to Te. 

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