Guanidines supported

The formation of a bis(guanidinate)-supported titanium imido complex has been achieved in different ways, two of which are illustrated in Scheme 90. The product is an effective catalyst for the hydroamination of alkynes (cf. Section V.B). It also undergoes clean exchange reactions with other aromatic amines to afford new imide complexes such as [Me2NC(NPr )2]2Ti = NC6F5. ... 

The guanidinate-supported titanium imido complex [Me2NC(NPr02l2Ti = NAr (Ar = 2,6-Me2C6H3) (cf. Section IILB.2) was reported to be an effective catalyst for the hydroamination of alkynes. The catalytic activity of bulky amidinato bis(alkyl) complexes of scandium and yttrium (cf. Section III.B.l) in the intramolecular hydroamination/cyclization of 2,2-dimethyl-4-pentenylamine has been investigated and compared to the activity of the corresponding cationic mono(alkyl) derivatives. 

The metathesis of symmetrical aliphatic carbodiimides is also catalyzed by tungsten imido complexes above 140 Other carbodiimide metathesis catalysts include Cr(ll)/Si02/ iminophosphoranes, imido circonocenes, guanidine supported titanium complexes and group 14 amide complexes. ... 

Schuchardi ct at. [22] have reported an interesting paper on the activity of guanidines supported on polystyrene in the iransesierificaiion of soybean oil with methanol. Three types of chloromethylatcd poly(styrene/divinylbenzene). namely macroporous PS (with 4.4 meq Cl/g). macroporous PS (with 4.15 meq Cl/g) and gel type PS (with 1.0 meq CFg). and a linear polystyrene with a spacer ann introduced by reaction with 1,6-dibromohexane (with 1.5 meq Br/g). were utilized to immobilize TBD. TMG and dicyclohexyl guanidines (Figure 2). 

An unusual porphyrin-supported hafnium guanidinate was obtained from the reaction of (TTP)Hf=NAr (TTP = meso-tetra-p-tolylporphyrinato dianion, Ar = 2.6-diisopropylphenyl) with 1,3-diisopropylcarbodiimide. The molecular structure of the product, (TTP)Hf[Pr NC(NPr )(NAr)] is shown in Figure 24. ° ... 

The feasibility of identifying these edges of water base pairs has been supported by our studies of mitomycin C interacting with the model system for AT base pairs 29). Interactions of either component with mitomycin C are not observed but a complex is formed when all three components are present. Chemical shift changes observed in the NMR spectra support the structure 47 for the termolecular complex. The broader implication is that mitomycin C will likewise recognize the minor groove side of a G-C pair (it is known to alkylate the guanidine on this side)31 ... 

Aminosilicas have been widely studied for use in catalysis, either as a base catalyst or as a support for metal complexes (12). For example, amine functionalized silica can be used to catalyze the Knoevenagel condensation, an important C-C bond forming reaction. Also, the amine sites on the silica can be further functionalized to form supported imines, guanidine, and other species... 

The final conditions were scaled up with no problems chalcone 8a and guanidine (liberated from its hydrochloride with sodium ethoxide) were heated in dimethyl acetamide while bubbling air through the mixture to form pyrimidine 9a. After complete conversion (16 h), the product was cleaved from the support (20% trifluoroacetic acid in DCM). Pure 4-(2-amino-6-phenyl-pyrimidin-4-yl)bcnzamidc 1 was obtained as its trifluoroacetate salt upon evaporation of the filtrate and recrystallisation of the residue from ethanol/water in 56% overall yield based on the solid phase attached 4-carboxybenzaldehyde 6a. 

Scheme 7.6 Synthesis of di- and trisubstituted guanidines on a modified four-arm PEG-support.

Ishikawa and co-workers also reported a class of structurally modified guanidines for promotion of the asymmetric Michael reaction of ierf-butyl-diphenylimino-acetate to ethyl acrylate [124,125]. In addition to a polymer support design (Scheme 69), an optical resolution was developed to achieve chiral 1,2-substituted ethylene-l,2-di-amines, a new chiral framework for guanidine catalysis. The authors discovered that incorporating steric bulk and aryl substituents in the catalyst did improve stereoselec-tivitity, although the reactivity did suffer (Scheme 70, Table 4). 

In 2005, Jerome and co-workers investigated the selective monoesterification of sucrose with various fatty methyl esters, in the presence of a strongly basic guanidine (triazabicyclo[4.4.0.]dec-5-ene (TBD)) grafted either over silica (HMS-TBD) or a polystyrene support (PS-TBD) (Scheme 12) [129]. 

Scheme 12 Selective esterification of sucrose over silica-supported strongly basic guanidine sites...

Reliable antidotes for botulism are not available. In some cases, anticholinesterase drugs may improve muscle strength, albeit temporarily. Guanidine and 4-aminopyri-dine also have limited usefulness. Management depends primarily on supportive measures, such as administering antitoxin and maintaining respiration. 

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