Amido Substituents

Ireland-Claisen Rearrangement of a-Amido Substituted Allylic Esters 

The reaction conditions were optimized carefully with respect to the yield and diastereoselectivity. The standard conditions proved to be the best by both criteria. Deprotonation of the ester 106a with LDA (2.1 equiv) in THF at -75 °C, silyla-tion with MejSiCl after 10 min, and warming to reflux for Ih provided the rear- 

General Procedure for Ester-Enolate Claisen Rearrangements  

3-Methyl-2-[[(1,1-Dimethylethoxy)carbonyl]amino]-4-Pentenoic Acid (107a) 

Regarding the yield, the Ireland-Qaisen rearrangement of the silylated allylic ester 117a under standard conditions was superior to the chelate Claisen rearrangement discussed in the next chapter. 

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This method, sometimes referred to as transmetallation, is by far the most versatile synthetic route to transition metal amide complexes. The amide, typically lithium or sodium, is reacted with the corresponding transition metal halide either in a hydrocarbon or, more typically, an ether solvent. The method has been applied to virtually all of the transition elements and normally results in complete substitution except for the most bulky amido substituents (equations 12,37 13,38 14,39 1540... 

KDN, a rare sialic acid that is characterized by the presence of a hydroxy group at the 5-position rather than the more customary amido substituent, is undergoing a resurgence of interest as a possible cancer marker in humans, having been found on... 

Alkyl, aryl, silyl and amido substituents are all amenable to the in situ reduction protocol and similar RM compounds may also be made from univalent hahdes. The structures of the compounds produced in such reactions are dependent on the nature of the substituent for most substituents, oligomeric polyhedral clusters are obtained. The use of sterically... 

Introduction of a phenyl amido substituent affords mixtures of both the prone and supine isomers with the prone being slightly favored (Scheme 6).23 A combination of two-dimensional NMR experiments has established that in the prone isomers the diene is best described as a tt2, rf diene ligand, consistent with Ti(ll). In the supine cases, the spectroscopic data suggest more a2, tt character, indicative of a Ti(rv) metallocycle. When treated with B(C6Fs)3, [PhMe2NH][B(C6Fs)4], or MAO, 29 and 31 are active for the random co-polymerization of ethylene and 1-octene. 

Alternatively, a w r-structure with the amido atoms in apical positions is also possible. The found twisted fac structure equilibrates rapidly in solution on the NMR timescale even at low temperature, presumably via the mer-structure. For Bu substituent on the amido nitrogen, the twisted fat structure is preferred because of the steric interactions between the Buc and the two equatorial R groups. With the less steric demanding groups Pr1 or cyclohexyl as amido substituents, w r-structures have been found in the solid state. 

The synthesis of the Ind-amido titanium complexes [(C9H5R)SiMe2NBut]TiX2 (Scheme 304) with alkoxo and amido substituents at 2- and 3-indenyl position has been reported and the molecular structures of the derivatives for R = NMe2 and N(CH2)4 have been determined by X-ray diffraction. The methyl derivatives are activated with B(C6F5)3 and studied as catalytic systems for the ethylene/l-octene co-polymerization. A dramatic effect of the indenyl substituent nature on catalyst efficiency and polymer properties is observed.740... 

Cp-amido titanium complexes containing different amido substituents including amino functionalities (Scheme 310) have been prepared by the appropriate synthetic route and spectroscopically and structurally characterized. In some cases, intramolecular coordination of the amino-nitrogen atom is observed according to the X-ray diffraction data. These complexes when activated with MAO are catalytically active for ethylene polymerization.753... 

Section C. Halogen, Nitroso, Amino, Imino, Azo, and Amido Substituents. 443... 

Additional examples, shown in Scheme 5.2.25, illustrate a-chelation control in the formation of 111 and 114,36 37 as well as the inclusion of chirality in the y-alkoxy substituent in 115 leading to 116,3 a role for coordination in the case of the a-amido substituent of 118, which yields selective formation of diol derivative 119 via 121.39... 

Lithium Halide-catalyzed Reversal via Betaine Lithium Halide Adducts. This is the most common mechanism for loss of stereospecificity under Wittig conditions and often contributes to the stereochemical outcome of bezaldehyde reactions in the presence of lithium ion. The process is most facile for ylides containing anionic (alkoxide, carboxylate, or amido) substituents. 

The effectiveness of the secondary orbital interactions on the selectivity of cyclopropanation reactions was demonstrated by the exclusive formation of 28 in the reaction of 17 with ( )-Me2NC0CH=CHC02Me. Simple Hiickel calculations show that the highest coefficient of the HOMO of the aUcene is located at the amido group, and thus despite the smaller steric demand of the ester group, the amido substituent lies syn with respect to the phosphino group. 

Pyrano[3,4-i]indol-3-ones also react with alkenes having electron-donor substituents such as ethyl vinyl ether, vinyl acetate, dihydropyran and iV-vinylpyrrolidone. The oxygen substituents are eliminated to provide fully aromatized carbazoles. The amido substituent, on the other hand, is retained (Scheme 153) <92JCS(pi)415>. 

Similarly, photolysis of the complex TpW( = CH Bu)Cl(NPh) induces rotational isomerism of the alkylidene ligand and proton transfer to generate TpW( = C Bu)Cl(NHPh). The syn orientation of the amido substituent and the alkylidyne ligand positions the amide proton distal to the alkylidyne ligand, disfavouring the reverse tautomerisation reaction without prior amide rotation or catalysis. 

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