1.3.5- Triazine formamidines

Der hier gegebene Reaktionsmechanismus macht gleichzeitig das bei der Anwendung freier Amidine beobachtete Auftreten 2.4-disubstituier-ter s-Triazine (LXVIII) erklarlich, indem zwei Mole des Zwischenpro-duktes LXIVa unter Austritt der Nebenprodukte Ammoniak und Formamidin miteinander reagieren. 

Amino-4-cyano-4-methyl-4/f-l,2,3-triazole (291) reacts with formamidine at room temperature to give the substituted l,2,3-triazolo[l,5-a]-l,3,5-triazine (293) via a translocative rearrangement of the presumed intermediate (292) (Scheme 56) <85JOC4986>. 

Azirine derivatives 318 were shown in the same article to be precursors of triazines 324 (30-35% yield) and pyrimidines 326 (30% yield) upon treatment in DMSO with guanidine and formamidine, respectively (Scheme 71). A similar pathway to that outlined above is also invoked to explain these results thus, intermediate 323 would yield 324 by electro-cyclic ring closure, whereas 326 would be formed by heterocyclization of 325 and loss of ammonia (91JOC7). 

Nucleophilic attack at the fully conjugated 1,3,5-triazine usually results in ring cleavage. Thus, active methylene compounds react with 1,3,5-triazine in aminomethylenation reactions. A three-component reaction of cyclopentadiene with 1,3,5-triazine and a secondary amine leads to /V,7V-di substituted pentafulven-6-amines (304) and N2-(6-pentafulvenyl)formamidines (305)... 

Substituted amidines are of limited use in the synthesis of symmetric 1,3,5-triazines. Only formamidine or amidines bearing strongly electron withdrawing groups react readily. The proposed mechanism (59JA1466) resembles that of the trimerization of imidates (Scheme 87). 

Pyridyl)-l,3,5-triazine may be prepared from 4-cyanopyridine and formamidine via the imidate (163 Scheme 101) (80JHC333). 

When the dihydro-1,2,4-triazinone (194) is heated at 180 °C under reducing conditions there is rupture of the 1,2-bond followed by ring closure, producing 4,5-diphenyl-imidazolinone (195). Such reductive ring closures of benzotriazine 1-oxides (196) can give benzimidazoles, in particular 2-(4-thiazolyl)benzimidazoles (197) ( thiabendazole ). Similar reactions take place with 1,3,5-triazines. In fact, primary amines cleave the compounds completely with evolution of ammonia and formation of iV.iV -disubstituted formamidines. With suitable primary amines, though, this reaction can be designed to produce imidazolines or benzimidazoles (Scheme 113). 

Anilines and heterocyclic amines react with 1,3,5-triazine to furnish formamidines, e.g. (363) and (364) (Scheme 64). CH2-acidic compounds, e.g. nitriles, can be formylated by heating with 1,3,5-triazine. In the course of such reactions the enamines thus obtained can be converted to formamid-... 

Anstelle der einfachen Formamidine laBt sich auch 1,3,5-Triazin mit Erfolg zur Einfiih-rung von Aminomethylen-Gruppen in CH2-acide Verbindungen verwenden. Durch Er-... 

Triazine is inert towards electrophiles. However, nucleophilic attack occurs easily and opens the ring, but in the case of alkyl- and aryl-l,3,5-triazines, only under forced conditions. Typical examples are the reaction of 1,3,5-triazine with primary amines leading to ring fission of the heterocycle into formamidine units 1,... 

Triazine, mp 80°C, forms colourless needles. It is prepared by thermal cyclocondensation of formamidine acetate and triethyl orthoformate [174] ... 

Two groups of investigators have found independently that acetals of dimethylformamide are excellent reagents for the preparation of esters and phenolethers under mild conditions 2,4-Disubst. s-triazines and trisubst. formamidines have been prepared with dimethylformamide diethyl acetal in particular There are other synthetically interesting derivatives of N,N-disubst. amides, e.g. their chlorides. They give a variety of valuable products, including heterocyclics, in a simple manner The most frequently used of these amide chlorides is dimethylchloroformiminium chloride, which has already been mentioned in last year s Trends... 

Phenyl isocyanate added at room temp, to N,N-dimethyl-N -( 2 thiazolin-2-yl)-formamidine in benzene, and the product isolated after 10 min. -> 2-dimethyl-amino-3-phenyl-3,4,6,7-tetrahydro-2H-thiazolo[3,2-a]-s-triazin-4-one. Y 91%. F. e. and products s. R. Richter and H. Ulrich, B. 103, 3525 (1970). 

N,N -Disubst. formamidines and 1,3-heterocyclics from amines and 1,3,5-triazine... 

Disubst. 1,3,5-triazines. Guanidine in abs. ethanol added dropwise at room temp, during 15 min. to dimethylformamide diethyl acetal, then heated to reflux at a bath temp, of 85° 2,4-diamino-s-triazine. Y 86%. F. e., also trisubst. formamidines, s. H. Bredereck, F. Effenberger, and A. Hofmann, B. 97, 61 (1964). 

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