Aldimines nitrogen

Asyminetric Induction with Chiral Substituents at the Aldimine Nitrogen... 

Several blocked diamines or amino-alcohols are commercially available. The aldimine is an aldehyde-blocked diamine. The ketimine is a ketone-blocked diamine. The oxazolidine is a five-membered ring containing oxygen and nitrogen. The oxazolidine ring shown below is an aldehyde-blocked amino alcohol. The basic synthetic concepts of an aldimine, a ketimine, and an oxazolidine are shown below ... 

It is not known whether the amine assists the elimination of the nitrogen, but that the iminium salt retains its stereochemistry has been demonstrated (709). When a mixture of 68 and 69of 1 5 ratio is treated with diazomethane, the ratio of 70 71 obtained in 75% yield and determined spectroscopically was still 1 5. The traw-N-isopropyl-N-methylisobutylidinium perchlorate (69) was prepared by alkylation of an aldimine salt with diazomethanc and... 

The [4-1-3] cycloaddition has also been realized in acceptors containing a nitrogen atom. While a,/ -unsaturated aldimines, and structurally flexible ketimine such as (87), generally only undergo [3-1-2] cycloadditions (see Scheme 24), the ketimine (112), which is rigidly held in a cisoid conformation, does give exclusively the [4-1-3] adduct azepine (113). On the other hand, the steroidal imine (114) produces a quantitative yield of a 1 1 mixture of the [4-1-3] and [3-1-2] cycloadducts (115) and (116), respectively (Scheme 2.31) [36]. 

Pyridoxal 5 phosphate enzymes are generally used when amino acids are supplied as sources of carbon or nitrogen. An aldimine is produced initially and is isomerized to... 

Depending on the steric bulk of the nitrogen bonded substituent, the reaction of 4 with pyridine-2-aldimines can also proceed by an intermolecular insertion of the silylene into the C-H bond of the acyclic CN group [19]. 

A ferrocenyl-based aldimine chelated dimethylzinc with its imino and oxygen atom to produce the tetrahedral dimethylzinc complex 44. Both zinc-carbon bonds are equidistant (1.974(2) A) and the zinc-oxygen donor bond (2.381(2) A) is substantially longer than the zinc-nitrogen counterpart (2.213(2) A) (Scheme 37).91... 

Rhodium complexes catalyze 1,2-addition of main group metal compounds to aldimines as well. Table 5 summarizes the reported methods. Electron-withdrawing substituents such as sulfonyl and acyl groups on the imino nitrogen atom are important to obtain sufficiently high reactivity. Asymmetric synthesis (diastereoselective and enantioselective) has also been accomplished. 

Fig. 6.4 Reversible interconversion of amino acid and keto acid. Conjugation of the imine bond in the aldimine with the electron sink of the pyridine ring plus protonation of the pyridine nitrogen as well as the metal ion - all this results in weakening of the C-H bond of the amino acid residue. Thus, also catalyzed is a-proton exchange, racemization of a chiral center at the a-carbon atom and decarboxylation of the appropriate amino acid. ...

After formation of the aldimine, numerous factors in the enzyme facilitate deprotonation of the a-carbon (Fig. 3, Step II). The lysine liberated by transimi-nation is utilized as a general base and is properly oriented for effective deprotonation [11]. Furthermore, the inductive effects of the ring system are tuned to increase the stabilization of the quinoid intermediate. For example, the aspartate group that interacts with the pyridyl nitrogen of the co enzyme promotes proto-nation to allow the ring to act as a more effective electron sink. In contrast, in alanine racemase, a less basic arginine residue in place of the aspartic acid is believed to favor racemization over transamination [12]. 

Breaking of bond b accounts for PLP-dependent decarboxylations. Decarboxylation of the intermediate aldimine is facilitated in the same way as loss of a proton in the transamination sequence. The pro-tonated nitrogen acts as an electron sink, and the conjugated system allows loss of the carboxyl proton. 

Early work on H chemical shifts of oximes, hydrazones, aldimines and ketimines has been collected286. It was shown that an oc-proton is always deshielded (increased 6 value) when it is cis relative to the group X at the nitrogen 1, compared to the trans orientation 2, with chemical shift differences varying between 0.2 and 1.35 ppm. The same is valid for R1 = H, where Ad is 0.3 to 1.0 ppm. 

Nitrogen lone pair effects on /HC values indicate aldimine and oxime configuration (see Section 4.1.1.2.). 

Keywords Catalyst, Alkylation, Allylation, Arylation, Mannich reaction, Carbon-nitrogen double bond, Imine, Nitrone, Aldimine, Organozinc reagents, Silyl ketene acetal, Silyl enol ether, Amine, (3-Amino acid... 

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