Precursor amide

Under conditions similar to those already outlined, stable aziridin imine derivatives, e.g. (422) and (423), can be prepared in excellent yields (70-80%) by treating the appropriate a-bromoamidines (easily accessible from the amide precursor) with potassium t-butoxide in ether <70AG(E)38l). At low temperatures the elimination proceeds with high regio- and stereo-selectivity at -40 °C (421) yields predominantly (422). 

Bis(phenolate) ligands are also present in two new lanthanide guanidinate complexes shown in Scheme 60, which were prepared by insertion of diisopropylcarbodiimide into the Ln-N bonds of appropriate neutral lanthanide amide precursors. ... 

A half-sandwich titanacarborane guanidinate complex is formed on treatment of the corresponding amide precursor with 1,3-dicyclohexylcarbodiimide (Scheme 106). The compounds have been employed as catalysts for the guanylation of amines (cf. Section V.C). ... 

In classical organic chemistry, nltrosamlnes were considered only as the reaction products of secondary amines with an acidified solution of a nitrite salt or ester. Today, it is recognized that nitrosamines can be produced from primary, secondary, and tertiary amines, and nltrosamides from secondary amides. Douglass et al. (34) have published a good review of nitrosamine formation. For the purposes of this presentation, it will suffice to say that amine and amide precursors for nitrosation reactions to form N-nitroso compounds are indeed ubiquitous in our food supply, environment, and par-... 

Because they are intermediates of the conventional OMVPE growth of the nitrides, Lewis-base adducts and dimeric or oligomeric amide precursors have thus been investigated as SMPs for nitride growth in some detail (Table 1). However, films of reasonable quahty have only been deposited for AIN using MesAl- NH3 and (Me2AlNH2)3. 

In addition the films were amorphous, but this result indicates that the activation energy of the deposition may be lowered significantly when amide precursors are used. The reason is facile transamination reactions. In this sense, the amide [Ga(NMe2)3]2 is not a true SMP for GaN but a good choice for depositing amorphous GaN at very low temperatures. 

Table 29 Synthesis of amide precursors 307b-m for the synthesis of 11 -aza-9-desmethyiartemisinin derivatives 308b-m <1995JME5038>...

At all levels of theory, the N-acetyl group of N-acetyl-N-arylnitrenium ions is rotated out of the plane of the aromatic ring, although to different extents." The N-acetyl group destabilizes the ion by ca. 20 kcal/mol relative to an N-methyl substituent in comparison with the neutral amide and amine precursors. This destabilization was attributed by Ford and Herman to loss of resonance in the amide precursor on going to the nitrenium ion, not to inductive destabilization of the ion by the acyl group. 

Amorphous UFPs of n-SiCcNvO and crystalline GaN UFPs can be synthesized by thermal decomposition in NH3 gas from the precursor hexamethyldisilazane (55), and from an amide precursor, [Ga2(NMe2)6,Me=CH3l (56), respectively. 

Common synthetic routes to beryllium amides, which were summarized in Ref. 1, involve the direct or indirect amination of beryllium hydride, beryllium chloride, a beryllium alkyl or amide precursor. Beryllium amides with bulky substituents are generally synthesized via the trans-metallation of beryllium dichloride with the lithium amides. The reaction of beryllium dichloride with secondary amines in the presence of an alkyllithium represents a less common synthetic route to beryllium amides. The formation ofbery Ilium amides via the reaction of an alkyl beryllium as well as beryllium hydride species with amines is also known. ... 

In this respect, Scheme 27, the ring opening of /V-sulfonyl p-lactam 80 with a dipeptide affords a-keto amide precursor 81. Subsequent elaboration of 81 and final hydrolysis of the ketal moiety affords poststatin 82, a naturally occurring pentapeptide which shows inhibitory activity against prolyl endopeptidase. 

Microcrystalline imides, e.g., Lao.eeeNH [44b] and imide-nitrides, e.g., Ce3(NH)3N [49b] were obtained by thermal decomposition of amide precursors. 

At this point the author would like to emphasize the importance and flexibility of the silylamide route. Ln(tritox)3 complexes are readily available from Ln[N(SiMe3)2]3 only for the larger lanthanide elements. However, the decreased steric bulk in Ln[N(SiHMe2)2]3(THF)2 amide precursors also allows the isolation of Ln(tritox)3 complexes of the smaller lanthanide elements [16, 40]. 

It has been demonstrated that intermediates 89 reacted with their lithium amide precursors to give the new intermediates 90, which are the real precursors of the resulting formamides 91 (Scheme 23)94. 

So far, chiral lithium amides for asymmetric deprotonation have found use only with a few types of substrates. The following sections deal with deprotonation of epoxides to yield chiral allylic alcohols in high enantiomeric excess, deprotonation of ketones, deprotonation of tricarbonylchromium arene complexes and miscellaneous stereoselective deprotonations. These sections are followed by sections in which various chiral lithium amides used in stereoselective deprotonations have been collected and various epoxides that have been stereoselectively deprotonated. The review ends with a summary of useful synthetic methods for chiral lithium amide precursors. 

The search for new chiral bases yielding even higher enantioselectivities has resulted in a number of more complex diamines as amide precursors. For example, Asami and coworkers designed the chiral base 14, which in the rearrangement of cyclohexene oxide 1 gave (,S )-cyclohexen-2-ol ((S)-2) in 89% ee (Scheme 10)2°. This result was a significant... 

Majewski and coworkers developed polymer-supported chiral lithium amides and applied them to the aldol reaction (Scheme 33)74. The amide precursor amines were prepared either from the insoluble Merrifield resins or from copolymerized styrene and 4-chloromethylstyrene yielding soluble polymer (SP). 

The oxyamination and diamination procedures described so far suffer from two important limitations. They require a stoichiometric quantity of osmium reagents and it is difficult to remove the tert-alkyl group from the product. Hence, procedures that employ catalytic amounts of osmium tetroxide for the preparation of vicinal hydroxy 4-methylbenzenesulfon-amides, precursors of /1-hydroxy amines, have been developed. 

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