Carbon-nitrogen bonds Subject

Similar reactions are known of compounds in which the carbon-nitrogen bond is part of a heterocyclic nucleus.17 18 The oxygen atom of the reactive system may be replaced by a sulfur atom, with, however, some reduction in the tendency toward rearrangement. Allyl p-tolyl sulfide rearranges (XI —> XII) to the extent of 27% (50% based on sulfide not recovered) when subjected to refluxing at 228-264° for four hours.19... 

In the laboratory of T.-L. Ho, the total synthesis of the novel marine sesquiterpene (+)-isocyanoallopupukeanane was completed." In the endgame of the synthesis, it was necessary to install the isocyano group onto the tricyclic trisubstituted alkene substrate so that it will occupy the more substituted carbon atom (according to Markovnikov s rule). The Ritter reaction was chosen to form the required carbon-nitrogen bond. The alkene substrate was dissolved in glacial acetic acid and first excess sodium cyanide followed by concentrated sulfuric acid was added at 0 °C. The reaction mixture was stirred at ambient temperature for one day and then was subjected to aqueous work-up. The product A/-alkyl formamide was subsequently dehydrated with tosyl chloride in pyridine to give rise to the desired tertiary isocyanide which indeed was identical with the natural product. 

Carbon-nitrogen bond formation is an important subject in the organic synthesis [301], and hydroamination is an atom-efficient process for the generation of amines and imines from olefins, allenes, and alkynes. Titanium-mediated hydroamination was among the most useful protocols thus far developed for this reaction. By using unsymmetrical olefins and alkynes, the addition of HNR2 can in principle lead to two isomeric products, where the isomeric ratio is usually dependent on the type of titanium catalyst used. 

Oxidative attack on a carbon-hydrogen bond of an alkyl group a to a nitrogen atom is not restricted to saturated aliphatic amines. In fact X in an X-N-CH- structural subunit can be virtually any common atomic grouping that can be found in stable organic molecules. For example, w-carbon hydrogens of Aralkyl-substituted aromatic cyclic amines (119), aryl amines (120), amides (121), amidines (122), A-nitrosodialkylamines (123), etc. are all subject to oxidative attack, carbinolamine formation, and in most cases release of an aldehyde or ketone depending on the substitution pattern (1° or 2°)... 

Cyanosilylations of carbon-oxygen and carbon-nitrogen double bonds with cyanosilanes are very important synthetic reactions since the products, cyanohydrin silyl ethers and a-amino nitriles, serve as synthetic intermediates for a variety of natural products. A number of studies on these subjects have been reported in the last decade however, this review does not deal with carbonyl and imine cyanosilylations due to the availability of recent reviews and limited... 

As an example, we describe one of many similar experiments devised for assigning resonances in proteins, a subject that we take up in more detail in Chapter 13. This particular experiment is designed to correlate the frequencies within the H—15N—13C=0 portion of a peptide group and is appropriately called simply HNCO. The basic pulse sequence for HNCO is shown in Fig. 12.16. To simplify the notation, instead of I, S, and T, we identify the active spins as H, N, and C, and use K to denote the spin of ar-13C. In a peptide chain, one a carbon is bonded and spin coupled to the nitrogen and another a carbon is bonded and coupled to the carbonyl carbon atom. With recombinant DNA methods, the protein is uniformly and highly enriched in both 13C and 15N, so all of these spins need be considered. 

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