Amides From other starting materials

Infrared spectroscopy is used as a monitoring method when the resin is functionalized with linkers that have chemical groups that absorb in the IR spectral region, such as carbonyls, esters, amides, or oximes. IR spectroscopy has also been used to monitor quantitative loading of a resin by comparing the difference in absorbance between two peaks, one from the starting material and the other one from the final product [45]. 

The (2 + 2) photocyclodimerization of substituted olefins has provided some of the most striking examples of crystal-lattice control of the stereochemistry of a reaction. This may be exemplified by a selection of derivatives of 5-phenylbutadienoic acid (61), for which it is observed that the solid-state photobehaviors of the amide 62, the methyl ester 63, and the dichlorophenyl ester 64 differ entirely from one another each affords a single stereo- and regioisomer in high yield, but with different starting materials giving different types of products (130). In solution, irradiation of 63 or other photoactive dienes yields... 

ControUed-potential oxidations of a number of primary, secondary, and tertiary alkyl bromides at platinum electrodes in acetonitrile have been investigated [10]. For compounds such as 2-bromopropane, 2-bromobutane, tert-butyl bromide, and neopentyl bromide, a single Ai-alkylacetamide is produced. On the other hand, for 1-bromobutane, 1-bromopentane, 1-bromohexane, 1-bromo-3-methylbutane, and 3-bromohexane, a mixture of amides arises. It was proposed that one electron is removed from each molecule of starting material and that the resulting cation radical (RBr+ ) decomposes to yield a carbocation (R" "). Once formed, the carbocation can react (either directly or after rearrangement) with acetonitrile eventually to form an Al-alkylacetamide, as described above for alkyl iodides. In later work, Becker [11] studied the oxidation of 1-bromoalkanes ranging from methyl to heptyl bromide. He observed that, as the carbon-chain length is increased, the coulombic yield of amides decreases as the number of different amides increases. 

The earliest report on such lactim ether formation was from Sammes [72JCS(P1)2494], who converted piperazine-2,5-dione to 2,5-diethoxy-3,6-dihydropyrazine (173) with an excess of triethyloxonium fluoroborate. Subsequently, Rajappa and Advani (73T1299) converted proline-based piperazine-2,5-diones into the corresponding monolactim ethers. The starting material was a piperazinedione in which one of the amino acid units was the secondary amino acid proline, and the other a primary amino acid. This naturally led to the regiospecific formation of a monolactim ether (169) (on O-alkylation) from the secondary amide, whereas the tertiary amide remained intact. This was later extended to piperazine-2,5-diones in which the secondary amino acid was sarcosine [74JCS(P 1)2122], leading to the monolactim ethers (170). 

On the other hand, a similar activation has been found to be practically possible when carbamates or amides instead of amines themselves are used as the starting materials. The a cation formed from carbamates and amides is sufficiently stable to be trapped by nucleophiles in solution 17). 

The starting material for the acylase process is a racemic mixture of N-acetyl-amino acids 20 which are chemically synthesized by acetylation of D, L-amino acids with acetyl chloride or acetic anhydride in alkaU via the Schotten-Baumann reaction. The kinetic resolution of N-acetyl-D, L-amino acids is achieved by a specific L-acylase from Aspergillus oryzae, which only hydrolyzes the L-enantiomer and produces a mixture of the corresponding L-amino acid, acetate, and N-acetyl-D-amino acid. After separation of the L-amino acid by a crystallization step, the remaining N-acetyl-D-amino acid is recycled by thermal racemization under drastic conditions (Scheme 13.18) [47]. In a similar process racemic amino acid amides are resolved with an L-spedfic amidase and the remaining enantiomer is racemized separately. Although the final yields of the L-form are beyond 50% of the starting material in these multistep processes, the effidency of the whole transformation is much lower than a DKR process with in situ racemization. On the other hand, the structural requirements for the free carboxylate do not allow the identification of derivatives racemizable in situ therefore, the racemization requires... 

The two major techniques for the preparation of triazolecarboxylic acids are the ami-drazone method and transformations or replacements of existing functions. In the former case one can introduce the carboxylic acid through starting materials such as (323). Alternatively, cyclization of other amidrazones can be accomplished with derivatives of oxalic acid, e.g. by converting the acylamidrazone (324) into the amide (325) from which the acid may be liberated by hydrolysis. A particularly convenient method for the preparation of carboxylic acids, esters and amides is the rearrangement arylazooxazolinones (Scheme 117). 

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