Guanidine aminal

Bignanidin 5-Isopropyl-l-(3-trifluor-methyl-phenyl)- E4, 1076 (Cyan —guanidin + Amin)... 

The only way to realize an enantioselective Biginelli reaction is to conduct it intramolecularly where the enantiopure urea and aldehyde portions are tethered. This reaction was the key step in L.E. Overman s total synthesis of guanidine alkaloid 13,14,15-lsocrambescidin 800. An optically active guanidine aminal was reacted with an enantiopure (3-keto ester in trifluoroethanol to afford 1-iminohexahydropyrrolo[1,2-c]pyrimidine carboxylic ester with a 7 1 trans selectivity between CIO and Cl3 positions. 

Guanidines. Amines are converted to guanidines (8 examples, 55-86%) by this reagent at room temperature in DMF (with Htinig s base). 

Asymmetric cyanohydrin synthesis remains an important reaction for organocatalysis and many of the catalyst classes discussed in subsequent chapters give highly effective catalysts for this reaction. These include Cinchona alkaloid derivatives, thioureas, guanidines, amine-oxides, diols and diamines. 

Figure 17 The M -independent Dz9-86 where bold Us, bold Cs, and bold As indicate nucleosides modified with guanidines, amines, and imidazoles, respectively. The red rC indicates a single embedded ribo-phosphodiester linkage.

The basicities in water and in aqueous surfactant solution of another 15 aryl-Pl(pyrrolidino) [(NC4Hs)3P=N-Ar] and aryl-Pl(dimethylamino) [(NMe2)3P=N Ar] phosphazenes (Ar = mono or di substituted phenyl rings) have been measured and correlated with previous data using acetonitrile and THE. A comparison with other bases such as guanidines, amines and pyridines showed that, in all cases, the phosphazenes were the strongest bases. The results confirmed earlier conclusions about the partly ylidic character of the NP double bond. Density functional theory calculations have shown that the phosphazenes (41) and (42) are very powerful neutral organic superbases at the site marked by an asterisc (the calculated pA a values in acetonitrile were 44.8 and 37.8, respectively). ... 

The synthesis of thiazolo[4,5-d]pyrimidines has been successfully accomplished by various methods. 4-Amino-5-ethoxycarbonylthiazole derivative has been cyclized to thiazolo[4,5-d]pyrimidine by its reaction with phenyl isothiocyanate [87], Many 4-amino-5-carbamoylthiazole derivatives have been cyclized to the corresponding thiazolo[4,5-d]pyrimidines using triethyl orthoformate/acetic anhydride mixture [88-91], Moreover, 4-amino-5-cyano thiazoles have been used to prepare the same fused ring system via their reaction with triethyl orthoformate, followed by treatment of the intermediate with hydrogen sulfide, guanidine, amines, and isothiocyanates [92, 93], Other thiazolo[4,5-d]pyrimidines have been obtained from 4-amino-5-cyano, carbamoyl, or ethoxycarbonyl thiazoles via cyclization with acetic anhydride [94] or formic acid [95],... 

Guanidines. Guanidines (10) were one of the first aniline derivatives used as accelerators. They are formed by reaction of two moles of an aromatic amine with one mole of cyanogen chloride. Diphenylguanidine (DPG) has enjoyed a resurgence ia demand as an activator for sulfenamides and a co-accelerator ia tire tread compounds which employ siUca fillers for low rolling resistance. Guanidines alone show too Htde activity to be extensively used as primary accelerators. There were no U.S. producers as of mid-1996. 

It is common practice in the mbber industry for a compounder to use combinations of several accelerators in developing a cure system. Typically these cure systems are comprised of a primary accelerator and one or more secondary types. Primary accelerators are generally the thiazole and sulfenamide classes the secondary types (kickers) are the thiurams, dithiocarbamates, guanidines, and to a much lesser extent, certain amines and the dialkylphosphorodithioates (20). 

Sulfenamide accelerators generally requite less fatty acid because they release an amine during the vulcanization process which acts to solubilize the zinc. Guanidines and similar amine accelerators also serve to both activate and accelerate vulcanization. 

Accelerators are chemical compounds that iacrease the rate of cure and improve the physical properties of the compound. As a class, they are as important as the vulcanising agent itself. Without the accelerator, curing requires hours or even days to achieve acceptable levels. Aldehyde amines, thiocarbamates, thiuram sulfides, guanidines, and thiasoles are aU. classified as accelerators. By far, the most widely used are the thiasoles, represented by mercaptobensothiasole (MBT) and bensothiasyl disulfide (MBTS). 

Although in the dry state carbon tetrachloride may be stored indefinitely in contact with some metal surfaces, its decomposition upon contact with water or on heating in air makes it desirable, if not always necessary, to add a smaH quantity of stabHizer to the commercial product. A number of compounds have been claimed to be effective stabHizers for carbon tetrachloride, eg, alkyl cyanamides such as diethyl cyanamide (39), 0.34—1% diphenylamine (40), ethyl acetate to protect copper (41), up to 1% ethyl cyanide (42), fatty acid derivatives to protect aluminum (43), hexamethylenetetramine (44), resins and amines (45), thiocarbamide (46), and a ureide, ie, guanidine (47). 

The Goodyear vulcanization process takes hours or even days to be produced. Accelerators can be added to reduce the vulcanization time. Accelerators are derived from aniline and other amines, and the most efficient are the mercaptoben-zothiazoles, guanidines, dithiocarbamates, and thiurams (Fig. 32). Sulphenamides can also be used as accelerators for rubber vulcanization. A major change in the sulphur vulcanization was the substitution of lead oxide by zinc oxide. Zinc oxide is an activator of the accelerator system, and the amount generally added in rubber formulations is 3 to 5 phr. Fatty acids (mainly stearic acid) are also added to avoid low curing rates. Today, the cross-linking of any unsaturated rubber can be accomplished in minutes by heating rubber with sulphur, zinc oxide, a fatty acid and the appropriate accelerator. 

This sequence is equally applicable to keto esters. Thus, condensation of guanidine with ethyl acetoacetate gives the pyrimidone, 134. Elaboration as above gives the pyrimidine, IJ5 acylation with the sulfonyl chloride (88) followed by hydrolysis yields sulfamerazine (107). Reaction of guanidine with beta dicarbonyl compounds gives the pyrimidine directly. Condensation of the base with acetonyl acetone affords the starting amine for sulfadimidine (108). ... 

DPTS-di-pentamethylene thiuram tetrasulfide TDD-thiodiazoIe derivative NC-fatty acid amide amine B-18-special curative DOTG-dior-tho-tolyl guanidine peroxide 14/40-dicumyI peroxide TAC-triallyl cyanurate. 

Both these materials are available commercially as powders and in impregnated wrapping papers and bags. Various modified inhibitors are also available, containing mixtures of the two, or more alkaline materials such as guanidine carbonate. Other proprietary inhibitors contain volatile amines, e.g. morpholine, combined with solution inhibitors. Certain solution inhibitors have been reported to act to some extent as volatile inhibitors. 

A useful route to 2,1,3-benzothiadiazoles is the F -catalyzed cyclization of l-(4-X-C6F4)-3-trimethylsilyl-l, 3-diaza-2-thiallenes [90JFC(50)359]. Fluoride ion catalysis is also used in the formation of heterocycles from pentafluorobenzoyl and -phenoxy compounds (81BCJ3447). Pentafluoro-phenylcarbonimidoyl dichloride with primary amines gave guanidines,... 

Borane, 1-methylbenzylaminocyanohydropyrrolyl-, 3, 84 Borane, thiocyanato-halogenohydro-, 3,88 Borane, trialkoxy-amine complexes, 3, 88 Borane, triaryl-guanidine complexes, 2,283 Borane, trifluoro-complexes Lewis acids, 3,87 van der Waals complexes, 3, 84 Borane complexes aminecarboxy-, 3,84 aminehalogeno-, 3, 84 amines, 3, 82, 101 B-N bond polarity, 3, 82 preparation, 3, 83 reactions, 3, 83 bonds B-N, 3, 88 B-O, 3, 88 B-S, 3, 88 Jt bonds, 3, 82 carbon monoxide, 3, 84 chiral boron, 3, 84 dimethyl sulfide, 3, 84 enthalpy of dissociation, 3, 82... 

When cyanogen bromide was used instead of CS2, the corresponding guanidines 169 were obtained under analogous conditions [108]. Moreover, differently substituted guanidines 171 could be obtained in very good yields when the isothiourea 168 was alkylated with Mel under microwave irradiation and the product treated with a primary amine. An intramolecular version of this reaction was also described for the preparation of structure 172 present in several important natural products (Scheme 61). 

Bicychc pyrazinones foimd in several natural products were synthesized via Michael addition of heterocyclic amines to nitro olefin followed by reduction/cyclization of the nitro group of the adduct [20] (Scheme 5). Further elaboration of the C-6 methoxycarbonyl group in pyrazinone to the n-propyl guanidine group could result in the synthesis of indoloperamine. 

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