Pyrimidine reactions

Benzopyridodiazines, 3, 199-262 Benzo-2-pyridone tautomerism, 2, 346 Benzo-4-pyridone tautomerism, 2, 346 Benzopyridones acylation, 2, 352 alkylation, 2, 349 Benzopyrido[3,2-ii]pyrimidine reactions... 

Imidazo[l,2-c]pyrimidine, 2,5,7-trichloro-nucleophilic displacement reactions, 5, 627 Imi dazo[ 1,2-a]pyrimidines pK, 3, 338 reactivity, 5, 627 synthesis, 5, 647 Imidazo[ 1,2-c]pyrimidines reactions, 5, 627 structure, 5, 610 synthesis, 5, 648-649 lmidazo[ 1,5-a]pyrimidines reactions, 5, 628 synthesis, 5, 649 lmidazo[l,5-6]pyrimidines synthesis, 5, 649-650 Imidazopyrrolopyridines bromination, 4, 506 lmidazo[4,5-6]quinoxaline nomenclature, 1, 22... 

Pyrazino[2,3-d]pyridazin-8-one, 5-chloro-synthesis, 3, 347 Pyrazino[l, 2-a]pyrimidine reactions, 3, 350 structure, 3, 339-340 synthesis, 3, 256, 365 Pyrazino[ 1,2-a]pyrimidine, 2-hydroxy-alkylation, 3, 351... 

Synthesis from pyrido[7,2-a/pyrimidines. Reaction of the disubstituted pyridopyrimidinone 416 with hydrazine gives the aminopyrazole-fused product 417 (Equation 153) <1996FA781, 2003JIC311, 2004IJB1561>. Similarly, substituent interaction in the pyridopyrimidine 418 with amines in toluene at reflux gives, in various proportions, diastereomeric mixtures of the pyrrolopyridopyrimidines 419 and 420 (Equation 154) <2003T4581>. 

A study of the a-arylation of diazine mono iV-oxides, under Heck-like conditions, also gave emphasis to pyrazines but a number of examples using pyrimidines and pyridazines were also described (Scheme 1). A wide range of aryl chlorides, bromides and iodides was used and the products were easily deoxygenated by catalytic reduction. An interesting feature was the use of a copper additive, which was only required for the pyrimidine reactions, to give a very substantial improvement in yield <06AG(I)7781>. 

Direct lithiation of pyridazine 132 followed by trapping with chiral sulfinate esters produced chiral sulfoxides 133, analogous to the pyrimidine reaction covered in Section 6.2.2.2 <99JOC4512>. Queguiner and co-workers demonstrated that a second lithiation/trapping sequence can provide fully substimted pyridazines 134 with high diastereoselectivities. 

Chloro, 3-bromo, 3-iodo, and 3-nitro derivatives of 5,7-dimethyl-pyrazolo[l,5-a]pyrimidine derivatives were prepared by chlorination, bromination, iodination, and nitration of 3-unsubstituted 5,7-dimethyl-pyrazolo[l,5-a]pyrimidines. Reaction with bromine and potassium thiocyanate gave a 3-thiocyanato derivative, which was converted into the mercapto derivative upon saponification. Nitrosation gives the 3-nitroso derivative and acylation with trifluoroacetic anhydride affords the trifluoroacetyl derivative (74JMC645 77JMC386). 

One final interesting preparation of pyrimido[5,4-ring transformation of pyrazolo[4,3-d]pyrimidines. Reaction of the A-oxides (272) with sodium ethoxide in.refluxing ethanol leads to the isolation of l,3-dimethyl-6-substituted pyrimido[5,4-[Pg.365]

Pyrimidines. Reaction of Thy with photoexited menadione or its electrochemical oxidation yields mainly to the N(l)-C(5)-linked dimer (Hatta et al. 2001). This can be accounted for if the precursor radical cation deprotonates at N( 1) (see above). For this N(l)-centered radical a second mesomeric form with the spin at C(5) can be written. Head-to-tail recombination leads to the isopyrimi-dine-type dimer [reaction (12)]. Isopyrimdines are unstable (see below) and add rapidly water [reaction (13)]. This dimer is also formed in the reaction with S04 , albeit with a lower yield. 

Pyrimidines, reactions with nucleophilic reagents 90UK888. 

The 3-methyl derivative of (142 R = H) was prepared by Krishnan ° from 2-aminopyridine and methyl methacrylate or methyl 3-bromoiso-butyrate. These reagents, however, were not able to transform the methyl derivatives of 2-aminopyridine to pyrido[l,2-a]pyrimidines. ° Reaction of 2-aminopyridine with ethyl 3-bromobutyrate and ethyl crotonate also was not successful. 

---