Dynamics of Diels–Alder reactions involving 2-trialkylsilyloxyfurans

Increasing the size of the silyl group on 2-trialkylsilyloxyfurans reduces the rate of Diels–Alder reactions with maleic acid derivatives. While the exo-adduct resulted from the reaction between 2-silyloxyfurans and maleic anhydride, endo-adducts resulted from the reactions with maleate esters. Analysis of transition state structures for the cycloaddition, calculated at the B3LYP/6-31G1 level of theory, revealed significant stretch-mode asynchronicity in the forming bonds, with selectivity arising from steric interactions that affect torsional strain about the shorter of the forming bonds.     

Stereoselective synthesis of α-methylenecyclopentenones via a Diels–Alder/retro-Diels–Alder protocol

A new procedure for the stereoselective synthesis of cross-conjugated dienones is reported. This method makes use of the Diels–Alder adduct of anthracene and dimethyl fumarate, a precursor to a spirocyclopent-2-enone anthracene adduct as the key intermediate. The addition of propyllithium or octyllithium to the key intermediate followed by a retro-Diels–Alder reaction furnished α-methylenecyclopentenones bearing a γ-propyl or γ-octyl side chain, respectively, in moderate yields and as single geometric isomers.     

Synthesis of heterocycles by domino-Knoevenagel–hetero-Diels–Alder reactions

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Asymmetric diastereoselective thia-hetero-Diels–Alder reactions of dithioesters

Asymmetric thia-Diels–Alder reactions involving new dithioesters bearing a chiral auxiliary are described, with diastereoselectivities up to 78%. Double-stereodifferentiating experiments employing chiral substrates in the presence of a chiral Lewis acid catalyst have been also carried out and, in this case, a diastereomeric excess of 90% was reached. The absolute stereochemistry of cycloadducts resulting from dithiooxalates and carbonyloxazolidinone dithioesters was assigned based on an X-ray structure and chemical correlation. In order to rationalize the sense of the chiral induction, stereochemical models for Cu(II)/bis(oxazoline)/dithioester complexes are proposed.     

Ring opening of dihydro-2-pyridones and intramolecular Diels–Alder reactions

A new ring-opening reaction of 5,6-dihydro-2-pyridones was discovered. Compounds 1 and 7 were converted to the dienoic amides 2 and 8 by reaction with sodium hydride at room temperature. N-Allylation of compounds 2 and 8 followed by IMDA reaction provided the cis-fused hexahydro-1-indolones 5 and 10, respectively. Treatment of compounds 5 and 10 with DBU in refluxing ethyl acetate gave the conjugated products 6 and 11, which were further transformed to the amides 12–15. The phenylthio group of compound 11 was substituted by a methyl group to give product 16.     

Dual Activation of Aromatic Diels–Alder Reactions

The unusually fast Diels–Alder reactions of [5]cyclophanes were analyzed by DFT at the BLYP-D3(BJ)/TZ2P level of theory. The computations were guided by an integrated activation-strain and Kohn–Sham molecular orbital analysis. It is revealed why both [5]metacyclophane and [5]paracyclophane exhibit a significant rate enhancement compared to their planar benzene analogue. The activation strain analyses revealed that the enhanced reactivity originates from 1) predistortion of the aromatic core resulting in a reduced activation strain of the aromatic diene, and/or 2) enhanced interaction with the dienophile through a distortion-controlled lowering of the HOMO–LUMO gap within the diene. Both of these physical mechanisms and thus the rate of Diels–Alder cycloaddition can be tuned through different modes of geometrical distortion (meta versus para bridging) and by heteroatom substitution in the aromatic ring. Judicious choice of the bridge and heteroatom in the aromatic core enables effective tuning of the aromatic Diels–Alder reactivity to achieve activation barriers as low as 2 kcal mol⁻¹, which is an impressive 35 kcal mol⁻¹ lower than that of benzene.     

Aluminosilicate Catalysis of Chalcone Diels–Alder Reactions

Previously unreported Diels–Alder adducts of substituted chalcones with isoprene and myrcene have been formed at more than 0°C by employing a nanoporous aluminosilicate catalyst. This catalyst eliminates problems with diene polymerization that are encountered with many other Lewis acids. The chalcone component has some size restrictions.     

Diels–Alder Reactions of β-Acylacrylic Acids

The Diels–Alder reaction of β-acylacrylic acids with dienes gave good yields and good regio- or stereoselectivity of the corresponding cycloaddition products with the use of Lewis acids.     

Enantioselective Synthesis of cis-Decalin Derivatives by the Inverse-Electron-Demand Diels–Alder Reaction of 2-Pyrones

A novel strategy for the synthesis of cis-decalins by an ytterbium-catalyzed asymmetric inverse-electron-demand Diels–Alder reaction of 2-pyrones and silyl cyclohexadienol ethers is reported here. A broad range of synthetically important cis-decalin derivatives with multiple contiguous stereogenic centers and functionalities are obtained in good yields and stereoselectivities. A full set of diastereomeric substituted cis-decalin motifs are readily accessible by tuning the absolute configurations of substituted silyl cyclohexadienol ethers (R or S) as well as the ligands (R or S). The synthetic potential is showcased by the enantioselective total synthesis of 4-amorphen-11-ol, and further demonstrated by the first total synthesis of cis-crotonin.     

Enhanced reactivity of tuned imidazolidin-2-one chiral auxiliaries in Diels–Alder reactions

Readily accessible alkyl 1-N-benzoyl-2-oxoimidazolidin-4-carboxylates display enhanced reactivity as efficient chiral auxiliaries in the Diels–Alder reaction of their 3-N-enoyl derivatives.     

由N-苯基[1,3]苯并噁嗪正离子与烯烃[4+2]反应合成喹啉并[1,2-c][1,3]苯并噁嗪-6-酮衍生物

以BF3·OEt2 为催化剂, 在室温下通过4-羟基-N-苯基[1,3]苯并噁嗪-2-酮的脱羟基产生N-苯基[1,3]苯并噁嗪正离子, 然后与富电子烯烃发生Diels-Alder反应, 合成出了一系列喹啉并[1,2-c][1,3]苯并噁嗪-6-酮和喹啉并[1,2-c][1,3]萘并噁嗪-6-酮衍生物.     

Synthesis of 4,5,6,7-tetrahydrobenzoxazol-2-ones by a highly regioselective Diels-Alder cycloaddition of exo-oxazolidin-2-one dienes with chalcones

The synthesis of novel of 4,5,6,7-tetrahydrobenzoxazol-2-ones is herein reported. They were obtained in moderate to good yields by a highly regio- and stereoselective Diels-Alder cycloaddition of N-substituted exo-oxazolidin-2-one dienes with chalcones or bis-chalcones as dienophiles.     

Cyanoacetylenes in reaction with benzimidazol-2-one

The reaction of 1-phenyl-2-cyanoacetylene and 4-hydroxy-4-methyl-2-pentynenitrile with benzimidazol-2-one was studied. The respective N,N-diadducts were obtained. It was shown that the addition of benzimidazol-2-one to the tertiary cyanoacetylenic alcohol catalyzed by bases is accompanied by intramolecular cyclization.Irkutsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, 664033 Irkutsk. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 6, pp. 1140–1443, June, 1992.     

Synthesis of 2-amino-6,7-dihydrothieno-[3′,2′:5,6]pyrido[2,3-d]pyrimidin-4-one

2-Amino-6,7-dihydrothieno[3′,2′:5,6]pyrido[2,3-rf]pyrimidin-4-one ( 1 ) was prepared in three steps from S-(3-butynyl)thiosemicarbazide hydroiodide ( 3 ) and diethyl ketomalonate. The featured step in this synthetic sequence was an intramolecular Diels-Alder reaction of the in situ generated 3-(3-butynylthio)-6-carboethoxy-5-chloro-1,2,4-triazine ( 9 ) to provide the key intermediate 5-carboethoxy-6-chloro-2,3-dihydrothieno-[2,3-b]pyridine ( 6 ). In the course of studies directed toward the preparation of 1 , thermolysis of 3-(3-butynyl-thio)-6-carboethoxy-1,2,4-triazin-5(2H)-one ( 2 ) was found to involve competitive intramolecular Diels-Alder and intramolecular coplanar cycloamination processes, providing the 2,3-dihydrothieno[2,3-b]pyridin-6(7H)-one ( 4 ) and the 1,3-thiazino[3,2-b]-1,2,4-triazin-3-one (5) derivatives, respectively.     

Synthesis and biological screening of 7-hydroxy-4-methyl-2H-chromen-2-one, 7-hydroxy-4,5-dimethyl-2H-chromen-2-one and their some derivatives

7-Hydroxy-4-methyl-2H-chromen-2-one (2), 7-hydroxy-4,5-dimethyl-2H-chromen-2-one (15) and their some derivatives were synthesized for exploring selected biological screening. The compounds 9 and 13 had shown high degree of cytotoxic activity. Three compound 9, 10 and 13 showed high degree of bactericidal activity amongst the present series.     

Highly regio- and stereo-specific preparation of a new carbohydrate-based 1,3-oxazin-2-one by the INIR method and its applications in some asymmetric transformations

Preliminary experiments show that a new gulonic acid-derived 1,3-oxazin-2-one, prepared by an intramolecular nitrene insertion reaction (INIR) method, serves to control both asymmetric aldol and Diels-Alder reactions with excellent stereo-selection.     

Synthesis of coumestan derivatives via FeCl3-mediated oxidative ring closure of 4-hydroxy coumarins

A concise and efficient approach to the syntheses of coumestan analogues has been developed. The underpinning strategy involves a FeCl(3)-mediated direct intramolecular oxidative annellation of 4-hydroxy-3-phenyl-2H-chromen-2-one derivatives. Utilizing this synthetic protocol, a variety of coumestan derivatives were conveniently obtained from readily available reagents.     

The use of umbelliferone in the synthesis of new heterocyclic compounds

New coumarin derivatives, namely 7-[(5-amino-1,3,4-thiadiazol-2-yl)methoxy]-2H-chromen-2-one, 5-[(2-oxo-2H-chromen-7-yloxy)methyl]-1,3,4-thiadiazol-2(3H)-one, 2-[2-(2-oxo-2H-chromen-7-yloxy)acetyl]-N-phenylhydrazinecarbothioamide, 7-[(5-(phenylamino)-1,3,4-thiadiazol-2-yl)methoxy]-2H-chromen-2-one and 7-[(5-mercapto-4-phenyl-4H-1,2,4-triazol-3-yl)methoxy]-2H-chromen-2-one were prepared starting from the natural compound umbelliferone. The newly synthesized compounds were characterized by elemental analysis and spectral studies (IR, 1H-NMR and 13C-NMR).     

A facile and efficient method for the synthesis of N-substituted isoindolin-1-one derivatives under Pd(OAc)2/HCOOH system

A facile and efficient method for the synthesis of N-substituted isoindolin-1-one derivatives from 2-formylbenzoic acid and amine under Pd(OAc)₂/HCOOH system has been described. The whole process is carried out in ligand-free conditions and furnished the desired products by reductive intramolecular cyclization. Furthermore, this procedure is applied successfully for the modification of natural products, such as vindoline and estrone.     

Vinyltriphenylphosphonium Salt Mediated One-Pot Stereoselective Synthesis of Dialkyl ( E )-2-(2-methyl-5-oxo-1-cyclopentenyl)-2-butenedioates

Protonation of the highly reactive 1:1 intermediates produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates by 2-hydroxy-3-methyl-2-cyclopenten-1-one leads to vinyltriphenylphosphonium salts, which undergo an intramolecular Wittig reaction to produce the corresponding cyclobutene derivatives. The cyclobutene derivatives are not isolable and undergo electrocyclic ring-opening reactions in CH 2 Cl 2 at room temperature to produce dialkyl ( E )-2-(2-methyl-5-oxo-1-cyclopentenyl)-2-butenedioates in moderate yields.