Imine nitrogen

TPP attack on pyruvate leads to decarboxylation. The TPP cationic imine nitrogen can act as an effective electron sink to stabilize the negative charge that must develop on the carbon... 

Under acidic conditions, the first step involves protonation of the imine nitrogen followed by tautomerization to form an ene-hydrazine intermediate (7). After the tautomerization, a [3,3]-sigmatropic rearrangement occurs, which provides intermediate 8. Rearomatization then occurs via a proton shift to form the imine 9 which cyclizes to form the 5-membered ring 10. Finally, loss of ammonia from 11 generates the indole nucleus in 12. 

Unlike the products of condensation of 1,2-diaminoethane and 1-amino-2-hydroxyethane with aminobutynones, which exist almost exclusively in the enole form, benzoxazoles 359,361 and benzothiazoles 360,362 are present in the solution as a tautomeric mixture of the ketone (359, 360) and enole (361,362) forms. This seems to be related to weakening of the imine nitrogen basicity due to adjacent oxygen and sulfur atoms. 

The suggested reaction mechanism involves a nucleophilic attack of the imine nitrogen at the activated triple bond, followed by a proton exchange, to give a benzimidazolinium system which, by intramolecular attack at the carbonyl group, leads to an epoxide that ring opens to the observed product. For the ethyl derivative (R = Et) a tub conformation could be established by X-ray crystallographic analysis.33... 

The stereochemical course of this reaction can be rationalized by Cram s cyclic model of asymmetric induction in which lithium is coordinated between the imine nitrogen and the 2-alkoxy group. 

The mechanism of the classic ketene-imine reaction to form /J-lactams [17,18] is thought to involve perpendicular attack of the imine nitrogen on the ketene carbonyl carbon from the side of the sterically smaller of the two groups, followed by conrotatory closure of the zwitterionic intermediate (Eq. 6). This... 

Formation of nitrones can be achieved in the first stage of a Krohnke type reaction in which p-n trosodi methy 1 an dine reacts with 2-oo-bromoacetylphenoxathiin in alkaline medium (336). The synthesis of a series of cyclic nitrones of structure (182) has been achieved by regioselective, and by an unusual [3 + 2] cycloaddition of a-nitrosostyrenes (181) to 1,3-diazabuta-l,3-dienes (180) (Scheme 2.64) (337a). Theoretical studies of the substitution effect at the imine nitrogen on the competitive [3 + 2] and [4 + 2] mechanisms of cycloaddition of simple acyclic imines with nitrosoalkenes have been reported (337b). 

Several pyridine containing ligands of this type have been reported by Toftlund [2]. A combination of two aliphatic and four imine nitrogen functions seems to provide a ligand field at the crossover point. A versatile class of ligands of this type is based on aliphatic diamines substituted with four alkylpyridine groups. The simplest compound of this type is tetrakis(2-pyri-dylmethyl)-l,2-ethanediamine (tpen) (18). 

Recently, Ohe and IJemura reported a novel approach to the catalytic cyclopropanation of alkenes via 2-furyl178 179 or 2-pyrrolyl carbenoids180 that originate from the intramolecular nucleophilic attack of a carbonyl oxygen or an imine nitrogen (ene-yne-ketone and ene-yne-imine precursor, respectively) on a 7t-alkyne complex or a cationic cr-vinyl complex. Initially, the group 6 complexes like Cr(CO)s were used. Soon it was found that a series of late transition... 

Nitrosation of 5-amenate derivatives has been reported to lead to unstable nitroso derivatives 123 that eliminate nitrogen spontaneously, forming the corresponding 5-olate analogues 124 [150]. Only in special cases the free bases of mesoionic 1,2,3,4-oxatriazolium-5-amenates, unsubstituted at the imine nitrogen, are stable enough to allow isolation and chemical characterization at room temperature [148]. 

Tris(phenylquinoxaline) compounds containing two imine nitrogens on a phenyl ring, possess high EA (2.6-2.8 eV), high mobility (10-4 cm2/(V s) at 106 V/cm), and good thermal stability. Star-shaped TPQ (91) was investigated for application as an ETM in a PPV-based... 

In the case of the Pd-bis-imine catalyst the isomerization process has a barrier of 5.8 kcai/mol [13c] for the generic system and 6.1 kcal/mol [16] for the real catalyst. The lower barrier is a result of the longer Pd-N distance (compared to the Ni-N bond length) which provides space for rotation of the olefin unit, even when the bis-imine nitrogens are attached to bulky substituents. 

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