Ketimine process

One of the most interesting waterborne systems is polyurethane (93). Polyurethane dispersions can be made by the following processes (94) acetone, prepolymer mixing, melt-dispersion (95), self-dispersion of solids, ketimine process (96), and ketazine process (97). The acetone... 

The ketimine of isophorone diamine is formed by reacting it with methyl isobutylketone, splitting off water in the process. When said ketimine is added to an isocyanate-terminated prepolymer based on IPDI, a semi-stable system is established with a pot life of several hours. The ketimine is a Schiff base and thus can react even in the absence of water. The complexities and advantages of this system are reviewed by Bock and Halpaap [75] ... 

Hedrick et al. reported imide aryl ether ketone segmented block copolymers.228 The block copolymers were prepared via a two-step process. Both a bisphenol-A-based amorphous block and a semicrystalline block were prepared from a soluble and amorphous ketimine precursor. The blocks of poly(arylene ether ether ketone) oligomers with Mn range of 6000-12,000 g/mol were coreacted with 4,4,-oxydianiline (ODA) and pyromellitic dianhydride (PMDA) diethyl ester diacyl chloride in NMP in the presence of A - me thy 1 morphi 1 i nc. Clear films with high moduli by solution casting and followed by curing were obtained. Multiphase morphologies were observed in both cases. 

The first example of an asymmetric reduction of C=N bonds proceeding via DKR was reported in 2005 by Lassaletta et al. In this process, the transfer hydrogenation of 2-substituted bicyclic and monocyclic ketimines could be accomplished via DKR by using a HCO2H/TEA mixture as the hydrogen source and a chiral ruthenium complex including TsDPEN ligand,... 

A ketimine can also be alkylated by the same process.140 In situ generation of a ketimine from the aromatic ketone 114 and benzylamine provides an efficient catalytic process with Wilkinson catalyst (Scheme 35). The alkylated aromatic ketone 115 is obtained in good yield. Better reactivity and selectivity are obtained with ketimine... 

Intramolecular process with rhodium catalyst has been described for the syntheses of indane, dihydroindoles, dihydrofurans, tetralins, and other polycyclic compounds. Wilkinson catalyst is efficient for the cyclization of aromatic ketimines and aldimines containing alkenyl groups tethered to the K z-position of the imine-directing group. 

The reductive alkylation reaction consists of a sequence of steps in which the hydrogenation is preceded by chemical processes. For primary amines, one forms the alcoholamine, which could proceed on to the ketimine. Hydrogenation of either the alcoholamine or the ketimine produces the secondary amine product,... 

A similar type of transformation is observed in a three-component reaction when ketimines, alkenes and carbon monoxide are reacted in the presence of Fe2(CO)9, as reported by Anders group. In these cases the cyclization process leads to unusual polycyclic spiro-heterocycles such as 32 shown in Scheme 9.25 [56, 57]. 

The participation of imines in this process has been demonstrated experimentally. In the presence of an oxidant, 227 reacts with specially prepared aldehyde imines or ketone imines 237 giving condensed pyrroles 236d j (Scheme 68) (01TL5981). Notably, in the case of ketimines yields of 236 are 72-80%. With aldimines they are substantially lower due to considerable tarring. 

The reductive-trimethylsilylation of imines by means of granulated lithium in THF at 0-5 °C is a good method to synthesize ASMA and RSMA. This process was applied to aldimines and ketimines, lower yields being obtained in the latter case.190... 

The possibility of employing a wide range of nucleophilic radical sources, including alcohols, the choice of ideal protecting groups for amines, and the possibility of extending this process to ketimines by the development of a catalytic system in which TiCLt is associated with Zn, enables us to anticipate new frontiers for the synthesis of new structural types of a-amino acids and other amino-derivatives of crucial importance for chemistry, medicine, and life. 

Here, too, the process involves several steps, and the enzyme must accelerate them all. The rate of the decarboxylation step itself certainly is faster in the ketimine salt than in the ketoacid. Taguchi (31) succeeded in preparing the Schiff base, I. Prior to his work, no j3-carboxy Schiff base was known, presumably because they decarbox-ylated too rapidly. 

Compound I could be isolated because the decarboxylation of the ketimine must produce an intermediate with a badly twisted double bond. The twist is imposed by the bicyclic structure the intermediate in the decarboxylation violates Bredt s rule. This slows the decarboxylation. Taguchi s Schiff base, nevertheless, undergoes decarboxylation about 106 times as fast as does the ketoacid from which it was made. The model accounts for the major part of the acceleration in the decarboxylation step for the overall process. 

Racemization of the Amino Acid Substrate Deprotonation of the a-carbon of the amino acid leads to tautomerization of the Schiff base to the quinonoid ketimine, as shown in Figure 9.2. The simplest reaction that the ketimine can undergo is reprotonation at the now symmetrical a-carbon. This is not a stereospecific process therefore, displacement of the substrate by the reactive lysine residue results in the racemic mixture of d- and L-amino acid. 

A novel oxazole to imidazole transformation occurs when the oxazole (168) reacts with the imidoyl chloride (169) in the presence of phosphoryl chloride. The process probably involves an initial quaternization of the oxazole with subsequent ring opening of the oxazolium salt to form a ketimine (170). Intramolecular nucleophilic attack then leads to the imidazole product (Scheme 96). 

The formation of pyrroles by the reaction of the cyclopropylketimine (63) with HBF4 has been studied from a mechanistic point of view using 3-chloropropionyl chloride enriched with at the carbonyl carbon atom The C-NMR spectrum of the pyrrole formed from the cyclopropyl ketimine (63) shows enhancement of the peak at the 5-carbon in accord with mechanism A outlined in Scheme 27. Operation of process B analogous to the vinylcyclopropane rearrangement 63a would have led to enrichment at the 3-carbon of the pyrrole product. 

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