An efficient synthesis of pyrrolo[2,3-d]pyrimidines via inverse electron demand diels-alder reactions of 2-amino-4-cyanopyrroles with 1,3,5-triazines

The scope of the inverse electron demand Diels-Alder reaction of 2-amino-4-cyanopyrroles (3a-e) with 1,3,5-triazines (1, 2) is reported. This methodology is suitable for one-pot syntheses of highly substituted and highly functionalized pyrrolo[2,3-d]pyrimidines that are the central heterocyclic nucleus of various nucleoside natural products such as toyocamycin, sangivamycin, and tubercidin.     

Synthesis of substituted fused pyridines, pyrazines and pyrimidines by sequential Ugi/inverse electron demand Diels–Alder transformations

The synthesis of all four regioisomers of fused pyrrolidino-pyridines in a one-pot two-step sequential Ugi-inverse electron demand Diels–Alder reaction is described. Fused pyrrolidino-pyrazines, pyrrolidino-pyrimidines and azepinone pyridines can also be obtained in consecutive synthetic sequences.     

Synthesis of fused uracils: pyrano[2,3-d]pyrimidines and 1,4-bis(pyrano[2,3-d]pyrimidinyl)benzenes by domino Knoevenagel/Diels-Alder reactions

Abstract  

Knoevenagel condensation of barbituric acids with aromatic aldehydes containing one or two formyl groups was carried out. 5-Arylidenebarbituric acids underwent smooth hetero-Diels-Alder (HDA) reactions with enol ethers to afford cis and trans diastereoisomers of pyrano[2,3-d]pyrimidine-2,4-diones and 5,5′-(1,4-phenylene)bis[2H-pyrano[2,3-d]pyrimidine-2,4(3H)-dione] derivatives in excellent yields (75–88 %). Syntheses were realized by Knoevenagel condensation and HDA reaction in four different reaction conditions: Knoevenagel condensation in water and Diels-Alder reaction in methylene chloride solution, Knoevenagel condensation in water and Diels-Alder reaction without solvent, three-component one-pot reaction in methylene chloride solution, or three-component one-pot reaction in water. All reactions were carried out without catalyst at room temperature. The reactions of malononitrile with Knoevenagel condensation products of barbituric acids and heteroaromatic aldehydes or terephthalaldehyde were examined and did not provide corresponding pyranopyrimidines.     

Polysubstituted 2,3-dihydrofuro[2,3-b]pyridines and 3,4-dihydro-2H-pyrano[2,3-b]pyridines via microwave-activated inverse electron demand Diels-Alder reactions

Polysubstituted 2,3-dihydrofuro[2,3-b]pyridines and 3,4-dihydro-2H-pyrano[2,3-b]pyridines have been synthesized from 1,2,4-triazines using the inverse electron Diels-Alder reaction. For this purpose, 3-methylsulfanyl-1,2,4-triazines were reacted with several nucleophiles allowing the formation of appropriately substituted alkynes to undergo the intramolecular inverse electron demand Diels-Alder reaction. Sealed-tube microwave activation of the cycloaddition reaction has proved to be very efficient and allowed shorter reaction times. This strategy enabled an efficient synthesis of 3-hydroxy-2,3-dihydrofuro[2,3-b]pyridines and 4-hydroxy-3,4-dihydro-2H-pyrano[2,3-b]pyridines with several points of diversity on the bicyclic scaffold.     

An efficient synthesis of pyrano [4,5-c] pyrrole derivatives through microwave—accelerated intramolecular Knoevenagal hetero Diels–Alder reaction

Synthesis of novel pyranopyrrole derivatives has been achieved by a one-pot IMHDA reaction of N-substituted aldehydes with various diones in the presence of ethylene diaminediacetate (EDDA) in excellent yields under mild conditions.     

Cyclisation of 3-alkenylpyrido[1,2-a]pyrimidines to furo[2,3-d]pyrido[1,2-a]pyrimidines

3-Alkenylpyrido[1,2-a]pyrimidines react under mild conditions to give novel tricyclic furo[2,3-d]pyrido[1,2-a]pyrimidines in high yields. The cyclisation takes place in the presence of an acid catalyst. The product yield is affected by the type and the strength of the acid used. Exceptionally high yields were obtained when an organic acid like trifluoromethanesulfonic acid and trifluoroacetic acid were used. On the other hand, sulfuric acid gave the best results of the inorganic acids examined.     

(R)-bis-Binaphthoxy iodo lanthanides as catalysts for Diels–Alder reactions

[(R)-1,1′bi-2,2′-Naphthoxy]LnI(THF)₂ (Ln: Yb, Sm, La) 5 have been prepared by reaction of the bispotassium salt of (R)-binaphthol with lanthanide triiodides, and characterized. They are active catalysts for Diels–Alder reactions although with low asymmetric inductions. The lanthanum iodo bisbinaphthoxide gives a slightly higher enantiomeric excess than the two other complexes.     

Iodine‐Catalyzed Synthesis of Cyclopenta[c]quinoline Derivatives via Imino Diels–Alder Reaction

A mild and efficient method for the synthesis of cyclopenta[c]naphtho[2,3‐f]quinoline and cyclopenta[c]pyrazolo[4,3‐f]quinoline derivatives via an imino Diels–Alder reaction of aromatic aldehyde, anthracen‐2‐amine, or 1H‐indazol‐5‐amine and cyclopentanone catalyzed by iodine is described. This novel procedure has the advantages of mild reaction condition, high yields, and metal‐free catalyst.     

Thieno[2,3-d]pyrimidin-4-ones 1. Condensation of 2,3-dimethyl- and 2,3-tri-, 2,3-tetra-, and 2,3-pentamethylene-7,8-dihydro-pyrrolo[1,2-a]thieno[2,3-d]pyriminidin-4(6H)-ones with aromatic aldehydes and furfural

2,3-Dimethyl- and 2,3-tri-, 2,3-tetra-, and 2,3-pentamethylene-substituted 8-arylidene-6,7-dihydro-pyrrolo[1,2-a]thieno[2,3-d]pyrimidin-4-ones were synthesized by the reaction of 2,3-dimethyl- and 2,3-tri-, 2,3-tetra-, and 2,3-pentamethylene-7,8-dihydropyrrolo[1,2-a]thieno[2,3-d]pyrimidin-4(6H)-ones with benzaldehyde, its 4-dimethylamino-, 3,4-dimethoxy-, and 3,4-methylenedioxy derivatives and also furfural in the presence of NaOH.     

Confinement induced thermodynamic and kinetic facilitation of some Diels–Alder reactions inside a CB[7] cavitand

The effect of geometrical confinement on the Diels–Alder reactions between some model dienes viz. furan, thiophene, cyclopentadiene, benzene, and a classic dienophile, ethylene has been explored by performing density functional theory‐based calculations. The effect of confinement has been imposed by a rigid macrocyclic molecule cucurbit[7]uril (CB[7]). Results indicate that all the reactions become thermodynamically more favorable at 298.15 K temperature and one atmospheric pressure inside CB[7] as compared to the corresponding free gaseous state reactions. Moreover, the rate constants associated with the reactions experience manifold enhancement inside CB[7] as compared to the “unconfined” reactions. Suitable contribution from the entropy factor makes the concerned reactions more facile inside CB[7]. The energy gap between the frontier molecular orbitals of the dienes and dienophiles decrease inside CB[7] as compared to that in the free state reactions thereby allowing facile orbital interactions. The nature of interaction as well as bonding has been analyzed with the help of atoms‐in‐molecules, noncovalent interaction, natural bond orbital as well as energy decomposition analyses. Results suggest that all the guests bind with CB[7] in an attractive fashion. Primarily, noncovalent interactions stabilize the host–guest systems. © 2017 Wiley Periodicals, Inc.     

Synthesis of 2H-benzo[g]furo/thieno/pyrrolo[2,3-e]indazoles via Intramolecular Dehydrogenation Photocyclization

A catalyst-,acid-and base-free,environmental-friendly method for synthesis of 2H-benzo[g]furo[2,3-e]indazoles,2H-benzo[g]-thieno[2,3-e]indazoles and 2H-benzo[g]...     

Synthesis of novel 5,6-substituted furo[2,3-d]pyrimidines via Pd-catalyzed cyclization of alkynylpyrimidinols with aryl iodides

A flexible method for the synthesis of 5,6-disubstituted furo[2,3-d]pyrimidine derivatives is described. The key step is a palladium-catalyzed arylative cyclization of alkynylpyrimidinols with various aryl iodides, which gave the title compounds in 36-75% yield.     

2-氨基噻吩并[2,3-d]嘧啶-4(3H)-酮衍生物的合成

丁醛(1)、氰乙酸乙酯、硫磺在三乙胺作用下制得2-氨基-4-乙基噻吩-3-羧酸乙酯(2), 2再与三苯基膦、六氯乙烷及三乙胺反应, 以84%的产率得到膦亚胺3. 应用膦亚胺3与芳基异氰酸酯的氮杂Wittig反应, 生成的碳二亚胺4, 再与仲胺作用得到中间体5, 而后在醇钠的催化下关环制得2-二烷氨基噻吩并[2,3-d]嘧啶-4(3H)-酮衍生物6, 产率为58%～82%.     

Substituted 2-aminonicotinamides in the synthesis of pyrido[2,3-d]pyrimidin-4(1H)-ones, 2,3-dihydropyrido- [2,3-d]pyrimidin-4(1H)-ones, and 11b,12-dihydropyrido- [2',3':4,5]pyrimido[2,1-a]isoindole-5,7-diones

The reactions of 2-aminonicotinamides with triethyl orthoformate, carboxylic acids chlorides, aldehydes, and 2-formylbenzoic acid were studied. As a result pyrido[2,3-d]pyrimidin-4(1H)-ones, 2,3-dihydropyrido[2,3-d]pyrimidin-4(1H)-ones, and 5,7,11b,12-tetrahydropyrido[2',3':4,5]pyrimido- [2,1-a]isoindole-5,7-diones were obtained.