Triazines Diels-Alder reactions

A total synthesis of fabianine, a simple terpenoid alkaloid, based on the implementation of an enamine 4-methyl-1,2,3-triazine Diels-Alder reaction has been detailed.850... 

Representative Intermolecular 1,2,4-Triazine Diels-Alder Reactions... 

Triazines biocides, 1, 398 Diels-Alder reactions, 2, 46 in non-silver photography, 1, 383 photolysis azetes from, 7, 283... 

The key step of an interesting synthesis of Sempervirine (327) is a triazine Diels-Alder annulation reaction with an enamine (88T3195). 1-... 

Phenylsulfonyl)indole 330 was converted to a ketone by a set of standard reactions followed by the selenium dioxide oxidation of the resulting acetyl goup to the ketoaldehyde 332 (Scheme 101). Methylthiosemicarbazide hydroiodide reacted with 332 to the triazine 333 in 83% yield. As Diels-Alder reactions with 1 -pyrrolidinocyclohexene failed, 333 was first oxidized... 

A special method, with only two examples, starts from 1,2,4-triazines.20 21 Diels-Alder reaction with the strained dienophile dimethyl tricyclo[4.2.2.02,5]deca-3,7,9-triene-7,8-dicarboxylate (14) is followed by an elimination of nitrogen via a retro-Diels-Alder process. The formed product, however, cannot be isolated, but reacts via another retro-Diels-Alder reaction and an electro-cyclic reaction to provide the azocine derivative 15. The sequence order of the reactions is not clear, but both pathways lead to the same product. 

Sauer and Heldmann [97] recently reported an interesting application of ethynyltributyltin as an electron-rich dienophile in an inverse electron-demand Diels-Alder reaction with the electron-deficient triazine derivative 94. This method is interesting because the reaction is highly regioselective and the trialkylstannyl group is easily replaced by several groups under mild conditions, leading to substituted pyridines 95 (Scheme 2.41). 

A Diels-Alder reaction of arynes with 1,2,4-triazines 102 allows the preparation of isoquinolines substituted with electron-withdrawing groups in the nitrogen-containing ring. The isoquinoline-1-carboxylic esters bearing additional substituents are of particular interest because they are not readily available by the usual routes [100,101] (Scheme 2.42). 

The inverse electron demand Diels-Alder reaction has also been used to provide expedient access to unnatural 6-carboline alkaloids from 1,2,4-triazines, prepared by microwave-assisted MCR [92]. One-pot reaction of an acyl hydrazide-tethered indole 73, 1,2-diketone and ammonium acetate in acetic acid provided triazines 74 (see Sect. 3.2, Scheme 22), bearing an electron-rich dienophilic indole moiety (Scheme 31). By carrying out the... 

The inverse electron demand Diels-Alder reaction of 3-substituted indoles with 1,2,4-triazines and 1,2,4,5-tetrazines proceeds in excellent yields both inter- and intramolecularly. The cycloaddition of tryptophan 124 with a tethered 1,2,4-triazine produced a diastereomerically pure cycloadduct 125 <96TL5061>. 

An even more complex pathway involving inverse-electron-demand Diels-Alder reactions between imidazoles and 1,2,4-triazines linked by a tri- or tetramethylene... 

Derivatives of the pyrimido[4,5-e][l,2,4]triazines at the 7-position were prepared (75JOC2329) by displacement of the respective chloro derivatives. Reaction of pyrimidotriazines 291 or 294 (R = S02Me) with acetylenic alcohols or amines gave azalumazines 292 or azapterins 295, respectively, with dienophilic side chains (88JOC800). Compounds 292 or 295 underwent intramolecular Diels-Alder reaction to give 6,7-annulated 5-deazapteridines 293 and 296, respectively (88JOC3568). 

Pyridine synthesis via hetero-Diels-Alder reaction of 1,2,4-triazines and dieno-philes (e.g. enamine) followed by extrusion of N2. 

However, when pyridyliminophosphorane (306a) is treated with phenyl isocyanate or isothiocyanate (Scheme 110), mixed carbodiimides are obtained, which are capable of an intermolecular Diels-Alder reaction resulting in triazine 308. The cycloaddition occurs specifically with one C = N double bond of the carbodiimide serving as the dienophile (77ZC371). 

C. Sulfur as an Auxilliary in the Diels-Alder Reaction of Triazines. 55... 

Indian workers described the synthesis of l,3,4-thiadiazolo[3,2-a]-5-triazine-5(//)-thiones (61) by a hetero Diels-Alder reaction between 2-(arylideneamino)-5-ethylthio-l,3,4-thiadiazoles (60) and aromatic isothiocyanates (Equation (2)) <94MI 410-0I>. Thiadiazoles can be reduced with sodium amalgam to the aldehyde thiosemicarbazone while lithium aluminum hydride will reduce mesoionic thiadiazoles all the way to the hydrazine <84CHEC-I(4)545>. 

PREPARATION AND INVERSE ELECTRON DEMAND DIELS-ALDER REACTION OF AN ELECTRON-DEFICIENT HETEROCYCLIC AZAOIENE TRIETHYL 1.2,4-TRIAZINE-3,5,6-TRICARBOXYLATE (l,2,4-Triazine-3,5,6-tricarbo orl 1c acid, triethyl ester)... 

DIELS-ALDER REACTION OF TRIETHYL 1,2,4-TRIAZINE-3,5,6-TRICARBOXYLATE... 

Diels-Alder reaction of triethyl l,2,4-triazine-3,5,6-tricarboxylate, 66, 150 Diels-/ lder reactions, 66, 40 Diethyl amine, 66, 145... 

---