Triazines insertion reactions

Insertion reactions of isocyanates into the C-NR2 bond of R2NCH2NHCOOR and R2NCH20R and into the C-OR bond in R2NCH(OR)2 are also known. In the reaction of (RS)2CHNR2 with isocyanates, an insertion into the C-SR bond occurs The cyclic trimer obtained from formaldehyde and aniline 254 reacts with phenyl isocyanate at 130 °C to give the 1,3,5-triphenylhexahydro-5-triazine-2-one 255. The reaction most likely proceeds by dissociation of the trimer to a 1,4-dipolar intermediate which adds phenyl isocyanate. 

Thermolysis of the thiadiazole (164) leads to elimination of isocyanate and sulfur giving the triazine derivative (167). If the thermolysis is carried out in the presence of phenols 2-aryl-benzimidazoles (168) are produced <85JCS(P1)1007>. The S—N bond of (157) is readily cleaved with both N- and C-nucleophiles. Thus, treatment of (157) with an excess of amine gives the sulfenamide (169) (Scheme 39) and reaction of (157) with active methylene compounds leads to derivatives of type (170) (Scheme 39) which on heating furnish (171). Cyanide ion inserts into the S—N bond of (164), probably via the intermediate (172) which immediately recyclizes to give the thiadiazinone (173) (Scheme 40) <85JCS(P1)1007>. 

The initial success of the inverse electron demand [4 + 2]cycloaddition reaction of electron deficient, 1,2,4-triazine (61) with a-aryl enamine (60) to formulate the 4-arylpyridine forms the basis of a complementary approach to the CDE ring system of lavendamycin. In this strategy the oxidative insertion of aryl halide bond to provide the p-carboline derivative in the presence of palladium (0) was the notable feature. In a recently published article by Boger, a total synthesis of lavendamycin starting from the precursor 63 has been presented. The utility of... 

The reaction mechanism was proposed as shown in Scheme 13. Reaction of an aniline with the lanthanide amide gave the new amido species through an acid-base reaction. A nitrile was then coordinated to the metal center, and then an intramolecular insertion of amide to cyano group of nitrile gave the corresponding intermediate. The intermediate underwent protonolysis by amine to release the product and regenerate the lanthanide amide as the active species. If the reaction of the intermediate with additional nitrile is more favorable than that with amine, triazine was produced as the main product. 

Cyclosilazane (R2SiNR) reacts with phenyl isocyanate at 60-90 °C to give the six-membered ring insertion products in high yield Silylated imines 289 react with one equivalent of isocyanate to give the insertion products 290, which on further reaction with a different isocyanate afford 5,6-dihydro-l,3,5-triazine-2,4(l//,3i/)-diones 291 with two different substituents . 

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