4-Imino pyrimidines

Numerous syntheses have also been reported for arabinofuranosyl nucleoside analogues, prepared either conventionally from arabinofuranosyl derivatives or via 2,2-anhydro-nucleosides obtained from appropriate ribonucleosides. 5-Aza-cytosine-D-arabinoside has been synthesized and found to show similar antiviral activity to Ara-C(arabinosyl-cytosine). 7-a-, 7-<3-, 9-0 -, and 9- 3-arabino-furanosyl derivatives of 3-deazaguanine have also been prepared, but none showed any anti-tumour activity. 9-(o -D-Arabinofuranosyl)-8-aza[2- C]-adenine, 7-(/3-D-arabinofuranosyl)-pyrrolo[2,3-d]pyrimidine-4(3//)-one (15)," l-(a-D-arabinofuranosyl)- and l-(/3-D-xylofuranosyl)-4-nitropyrazole, and Ot-arabino-nucleosides of 5-fluoro-cytosine and -uracil derivatives have also been prepared. An improved synthesis of 9-(/3-D-arabinofuranosyl)-2-fluoro-adenine has been reported. The ratio of o to 3 anomers obtained by phase-transfer reaction of 2,3,5-tri-O-benzyl-D-arabinofuranosyl bromide with 6-chloro-2-thiomethyl-7-deazapurine varied with the quaternary ammonium salt used as a catalyst, although the jU-anomer predominated in every case. 2,2-Anhydro-nucleosides have been used to prepare l-j3-D-arabinofiiranosyl derivatives of 5-alkylthio-uracils, 5-ethyl-cytosine, and 5-ethyl-uracil, 8-alkylamino-purines, and 2-aralkylamino-l,4-dihydro-4-imino-pyrimidine hydrochlorides (16). ... 

It has been established that in the Dimroth rearrangement of 2-imino-pyrimidines, water plays an essential role (65JCS7071). In water the imine is, in fact, in equilibrium with its hydrate, the carbinolamine 39. That participation of the hydrate is important is shown by the experimental fact that in dry tetrahydrofuran, acetone, dioxane, or ether, the imine is quite stable and is not inclined to undergo rearrangement. However, on addition of a little water, rearrangement occurs its rate is proportional to the concentration of the water (65JCS7071). 

Treatment of 2-imino-3-phenyl-4-amino-(5-amido)-4-thiazoline with isocyanates or isothiocyanates yields the expected product (139) resulting from attack of the exocyclic nitrogen on the electrophilic center (276). Since 139 may be acetylated to thiazolo[4,5-d]pyrimidine-7-ones or 7-thiones (140). this reaction provides a route to condensed he erocycles (Scheme 92). 

Refluxing, 5.6-dihydro-7H-thiazolo[3,2-a]pyrimidine-7-one (370j with isopropylamine led to 2-imino-3-[2-(isopropylaminocarbonyl)ethyl]-thiazoline (371) (108). Similarly. tetrahydrobenzothiazolo[3,2-fl][2.3-f>]-quinazoline is opened by potassium hydroxide, yielding 373 (Scheme 214)... 

This kind of nucleophilic reaction, when performed with 7H-thiazolo[3,2-a]pyrimidine-7-one (374), however, is reported to give 2-[(/3-aminoacryloyl)imino]-4-thiazoline (375) (Scheme 215) (273, 703),... 

The same amino compounds also underwent reactions with a series of 3-cyano-4-imino- and 3-cyano-4-oxo-piperidines to yield 4-amino-5,0,7,8-tetrahydropyrido[4,3-d]pyrimidines. . A tetra-hydropyTido[4,3-prepared from 4-amino-l-henzyl-3-cyano-d -piperidine (134) hy a simple one-step preparation. This method is of general application for the preparation of fused pyrimidines and previous papers in this field are listed by Taylor. ... 

Heating the 5-isocyano-l,3,4-thiadiazolo[3,2- ]pyrimidin-5-one 115 with 10% hydrochloric acid gave a mixture of the 5-imino-l,3,4-thiadiazolo[3,2- ]pyrimidin-7-one 116 (10%) and the l,2,4-triazolo[l,5-c]pyrimidine-5,7-dione 117 (35%) (91JHC489). Formation of 117 probably occurred through thiadiazole ring rupture of 116 and recyclizatioii with its imino function together with desulfurization (Scheme 43). 

The reaction of the fervenulin 1-oxides 100 with secondary amines results in contraction of the 1,2,4-triazine ring to form 2-amino-5,7-dimethylimidazo[4,5-e] pyrimidine-4,6(5/7,7//)-diones 101. The reaction of the same fervenulin 1-oxides 100 with ammonia leads to the 1,2,4-triazine ring cleavage product, 1,3-dimethyl-5-imino-6-isonitrosouracil 102 (94KGS1253). 

A 9 1 mixture of 2,4-difluoro-4-pentafluoroethyl-3-trifluoromethyl-2//-, and 2,4-difluoro-2-pentafluoroethyl-3-trifluoromethyl-4//-, as well as 2-pentafluoroethyl-3-trifluoromethyl-4-oxo-4//-pyrido[l,2-n]pyrimidine were characterized by H, and NMR (00JFC105). 2-Trifluoromethyl-3-cyano-4-imino- and -4-oxo-4//-pyrido[l, 2-n]pyrimidines were characterized by and F NMR (00MI27). 

Reaction of 4-imino-4/f-pyrido[l, 2-n]pyrimidine-3-carbonitriles 124 with NaN3 in the presence of NH4CI gave 3-(2-pyridylamino)-2-(I//-tetrazol-5-yl)acrylonitriles 125 (93MIP3). 

The 3-formyl group of 8-substituted 3-formyl-2-hydroxy-4//-pyrido[l,2-n]pyrimidin-4-one was reacted with (cyanomethyl)- and (terr-butoxycarbo-nylmethylene)triphenylphosphorane in THF, and with 5-aminotetrazole in boiling MeOH for 9h to yield ( )-3-propenenitrile, terr-butyl ( )-3-propenoate and 3-[(2//-tetrazol-5-yl)imino]methyl derivatives, respectively (OlMIPl). 

Acidic hydrolysis of 4-imino-3-cyano-2-trifluoromethyl-4//-pyrido[l,2-n]pyrimidines in boiling EtOH with aqueous hydrochloric acid afforded 4-0X0 derivatives (00MI27). 

Heating the crystalline salt 2-aminopyridinium propiolate (346) at 100 °C in the solid state led to a 10 9 mixture of 2/f-pyrido[l,2-n]pyrimidin-2-one and ( )-3-(2-imino-l,2-dihydro-l-pyridyl)acrylic acid (347). Analysis of differental scanning calorimetry data shows unambiguously that the reaction takes place in the solid state. An endothermic peak at 81.1 °C corresponds to a solid state reaction, and a peak at 122-123 °C is attributed to melting. The product ratio of 2//-pyrido[l, 2-n]pyrimidin-2-one and 347 is 1 2.5 at 60°C, and 1 1.4 at 80°C (94MI12). 

Cyclocondensation of 2-iminopiperidine and 3-aryl-2-propynylnitriles in THE or 5% MeCN/THF afforded 4-aryl-2-imino-6,7,8,9-tetrahydro-2H- and 2-aryl-4-imino-6,7,8,9-terahydro-4//-pyrido[l,2-n]pyrimidines in 70-98% and 2-30% yields, respectively (00OL3389). When the reactions were carried out in the presence of 2 equiv of NaHMDS the product ratio was reversed. 

Reaction of 2-aminopyridine with ethyl 2-cyano-3-ethoxy-3-methyl-, -3-ethyl-, -3-phenylacrylates and ethyl 2-ethoxycarbonyl-3-ethoxy-3-methyl-, -3-phenylacrylates in boiling xylene yielded 2-substituted 4/f-pyrido[l,2-u]pyrimidine-3-carbonitriles and -3-carboxylates (99MI7). Similar reactions of 2-aminopyridine with 2-cyano-3-ethoxyacrylonitrile and its 3-methyl, 3-ethyl, -3-phenyl derivatives in boiling MeCN afforded 4-imino-4//-pyrido[l,2-u]-pyrimidine-3-carbonitrile and its 2-substituted derivatives. 

Reaction of 3-amino-2-cyano-4-[(phenylamino)(methylthio)methylene]-2-pentenedioate (408) with a large excess of 1,3-propanediamine afforded ethyl 6-imino-l, 2,3,4-tetrahydro-6//-pyrido[l, 2-n]pyrimidine-9-carboxylate (409) as depicted in Scheme 16 (95JHC477). 

Reaction of 4-cyano-3-imino-2,3,5,6,7,8-hexahydro-l//-pyrido[l,2-c]pyr-imidin-l-one 169 with 2-chloroethyl isocyanate at ambient temperature and under reflux gave N-acylated 170 and tetracyclic derivative 171, respectively (95MI1). Similar reaction of 3-amino-4-cyano-2,4a5,6,7,8-hexahydro-l// pyrido[l,2-c]pyrimidin-1-ones 172 afforded tricyclic compounds 173. 

Chemical Name 2,3,3a,9a.Tetrahydro.3.hydroxy.6.imino.6H.furo[2, 3 4,5]oxazolo[3,2.a]. pyrimidine.2.methanol... 

The reaction is hindered by substitution in the 7-position, as revealed in the formation of 2e. Ynamine attack at the other imino moiety in the pyrimidine ring is even possible, which leads to 1,5-diazocines in an analogous reaction mechanism (cf. Section 1.5.). 

Figure 33-13. Synthetic derivatives of nucieoside triphosphates incapabie of undergoing hydroiytic re-iease of the terminai phosphoryi group. (Pu/Py, a purine or pyrimidine base R, ribose or deoxyribose.) Shown are the parent (hydroiyzabie) nucieoside triphosphate (top) and the unhydroiyzabie (3-methyi-ene (center) and y-imino derivatives (bottom).

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