Polar Cycloaddition Research Articles

Synthesis of Phenanthrenol Derivatives Through Polar Diels-Alder Reactions Employing Nitronaphthalenes and (E)-1-(Trimethylsilyloxy)-1,3- butadiene. Theoretical Calculations

The cycloaddition reactions between dinitronaphthalenes and (E)-1-trimethylsilyloxy-1,3-butadiene produce nitrophenanthrenol derivatives as principal products. The primary adducts suffer the irreversible lost of nitrous acid and, consequently, the aromatization. In these reactions it is frequent to observe the presence of naphthalenyl-1H-pyrrole derivatives as a result of a hetero Diels-Alder process, which is competitive with the normal way. The global electrophilic character of the dienophile is responsible of these results. Other dienes (or dienophiles/electrophiles) with electron donor substitution in C-1 show a different behavior in which the hetero Diels-Alder products prevail. In the series explored only the substrate 1-cyano-4-nitronaphthalene produces the naphthalenyl-1H-pyrrole derivative as principal product, probably as a consequence of its charge distribution. A combination between stereoelectronic effects in the electrophile and the type of substitution joint to the nucleophilicity of the diene is responsible of the results and regioselectivity observed in these polar cycloaddition reactions. In all the cases studied the regioselectivity expected by theoretical calculations corresponds with the ones obtained experimentally. Keywords: Phenanthrenols, Diels-Alder reaction, nitronaphthalenes, electrophiles, theoretical calculations.

Intramolecular Polar [4⊕+2] Cycloadditions of Aryl‐1‐aza‐2‐azoniaallene Salts: Unprecedented Reactivity Leading to Polycyclic Protonated Azomethine Imines

Intramolecular Polar [4^⊕+2] Cycloadditions of Aryl‐1‐aza‐2‐azoniaallene Salts: Unprecedented Reactivity Leading to Polycyclic Protonated Azomethine Imines

CYCLOADDITION OF DI(2-PYRIDYL) DITELLURIDE TO NORBORNENE STIMULATED BY ANTIMONY PENTACHLORIDE

The interaction of norbornene with the di(2-pyridyl) ditelluride–antimony pentachloride system in methylene chloride proceeds with the formation of exo -9-telluro-3-azoniatetracyclo-[9.2.1.0 2.10 .0 3,8 ]tetradeca-3(8),4,6-triene chloroantimonates(III), which are the products of polar cycloaddition of tellurium-containing electrophiles at the multiple bond. The structure of the heterocyclization products was established by X-ray structural analysis. Authors: A. V. Borisov, Zh. V. Matsulevich, V. K. Osmanov, G. N. Borisova, G. Z. Mammadova, A. M. Maharramov, and V. N. Khrustalev. English Translation in Chemistry of Heterocyclic Compounds , 2012, 48 (7), pp 1085-1089 http://link.springer.com/article/10.1007/s10593-012-1103-2

Polar cycloaddition of 2-pyridinetellurium trichloride to multiple bonds

A reaction of 2-pyridinetellurium trichloride with unsaturated hydrocarbons leads to [1,3]tellurazolo[3,2-a]pyridinium-4 derivatives — the products of polar cycloaddition of tellurium-containing electrophile at the multiple bond.

Cycloaddition of di(2-pyridyl) ditelluride to norbornene stimulated by antimony pentachloride

The interaction of norbornene with the di(2-pyridyl) ditelluride–antimony pentachloride system in methylene chloride proceeds with the formation of exo-9-telluro-3-azoniatetracyclo-[9.2.1.0 2.10 .0 3,8 ]tetradeca-3(8),4,6-triene chloroantimonates(III), which are the products of polar cycloaddition of tellurium-containing electrophiles at the multiple bond. The structure of the heterocyclization products was established by X-ray structural analysis.

The role of the trifluoromethyl group in reactivity and selectivity in polar cycloaddition reactions. A DFT study

The role of the trifluoromethyl group in reactivity, regio-, and stereoselectivity in cycloaddition reactions has been analyzed by studying the 1,3-dipolar cycloaddition (13DC) reactions of nitrone 4 with 3,3,3-trifluoro-1-nitropropene 7b and 3,3,3-trifluoro-2-nitropropene 14 using density functional theory (DFT) methods at the B3LYP/6-311G(d) level. The recent M06-2X functional has also been evaluated but, although the thermodynamic performance is improved, the kinetic data are not necessarily better than those obtained by the popular B3LYP functional for cycloaddition reactions. Four reactive channels associated with the meta and ortho regio- and endo and exo stereoselective approach modes of the nitro group of these disubstituted ethylenes relative to nitrone 4 have been explored and characterized. Unlike other electron-withdrawing groups, the trifluoromethyl group increases the reactivity of the nitroethylene, but it does not modify the meta and endo selectivities when it is located at the β conjugated position of nitroethylene. Analysis of the global and local electrophilicity indices allows for an explanation of the role of the trifluoromethyl group in reactivity and regioselectivity of electrophilically activated ethylenes.

Understanding the origin of the asynchronicity in bond-formation in polar cycloaddition reactions. A DFT study of the 1,3-dipolar cycloaddition reaction of carbonyl ylides with 1,2-benzoquinones

The origin of the asynchronicity in bond-formation in polar cycloadditions has been studied by an ELF analysis of the electron reorganisation along the 1,3-dipolar cycloaddition of Padwa's carbonyl ylide 4 with the 1,2-benzoquinone 8. This reaction presents an unexpected asynchronous bond-formation, which is initialised through the nucleophilic attack of Padwa's carbonyl ylide on the carbonyl oxygen atom of the strongly electrophilically activated 1,2-benzoquinone. The present study allows for the establishment that along an asynchronous bond-formation, the more favourable two-center interaction begins at the most electrophilic center, which is the center with the highest spin density achieved through the charge transfer process, and not, as expected, at the center that presents the larger positive charge.

Cycloaddition of 2-pyridinetellurenyl chloride to alkenes

The action of 2-pyridinetellurenyl chloride on alkenes results in the polar cycloaddition of the tellurium-centered electrophile at the multiple bond with the formation of 2,3-dihydro[1,3]tellurazolo[3,2-a]pyridinium derivatives.

CuI click catalysis with cooperative noninnocent pyridylphosphine ligands

We describe the synthesis and characterization of compound L1H, 2-di(tert-butyl)phosphinomethyl-6-methylpyridine, and the first dimeric CuI complex 3 with this novel bidentate NPtBu ligand. We also demonstrate for the first time that this ligand scaffold exhibits noninnocent reactivity through dearomatization behavior, similar to its well-studied tridentate analog L2H, 2,6-bis((di-tert-butylphosphino)methyl)pyridine PNPtBu. The molecular structure of [Cu(CCPh)(L2H)]2 is reported, which is a rare case of a crystallographically characterized copper-acetylide dimer. We also demonstrate that copper(I) complexes with either ligand L1H or L2H or their dearomatized counterparts may act as active, cooperative catalysts for the [2+3] polar cycloaddition of azides and acetylenes. These results represent the first indications of selective Cu-based cooperative catalysis, using non-innocent lutidine-based PNP backbone and catalysts 2 and 5 could thus be termed all-inclusive systems for this reaction.

Five-Membered Aromatic Heterocycles in Diels-Alder Cycloadditio Reactions: Theoretical Studies as a Complement of the Experimental Researches

The dienophilic behavior of electron-deficient substituted five-membered aromatic heterocyclices in polar cycloaddition reactions is studied from a theoretical point of view employing the global electrophilicity index to estimate the electrophilic character of the dienophiles and to compare them with the available experimental information. The type of substitution on the heteroatomic ring is also discussed. Complementary some new reactions of these substrates are described. Keywords: Five-membered aromatic heterocycles, dienophiles, polar-Diels-Alder, electrophilicity index, five-membered, acetylenedicarboxylate, heterocyclopentadienes, Danishefsky's diene, nitro-substituted, benzothiophene, nitroselenophenes

The 1,3-dipolar cycloaddition of 1 H-pyridinium-3-olate and 1-methylpyridinium-3-olate with methyl acrylate: a density functional theory study

The 1,3-dipolar cycloaddition reaction of 1-substituted pyridinium 3-olates with methyl acrylate is studied using density functional theory (DFT) method at the B3LYP/6-31G(d) level. The molecular mechanisms of the possible stereo- and regio-chemical pathways are characterized and explored. Solvent effects are also evaluated by the polarizable continuum model (PCM). Analysis of the results shows that there are relevant differences in the reaction pathways between the gas phase and with solvent. Only results in solvent phase are in accord with literature experimental results where 6-substituted 8-azabicyclo[3.2.1]oct-3-en-2-ones are formed preferentially. These polar cycloaddition reactions take place through highly asynchronous transition states in which nucleophilic attack by C2/C6 of the pyridinium-3-olates on the more electrophilic centre of the methyl acrylate initiates the process. Analysis of global and local indexes of the reactants is evaluated in order to explain the observed regioselectivity. Rate constants are calculated at room temperature using conventional transition state theory.

ChemInform Abstract: Synthesis of Thiochromans by Means of a (4+ + 2)Polar Cycloaddition of m-Tolylthiomethyl Chloride with Substituted Alkenes: A Simple Synthesis of (.+-.)-Cuparene and Related Sesquiterpenoids.

(±)-Cuparene, (±)-α-cuparenone, and (±)-tochuinyl acetate were synthesized from m-tolylthiomethyl chloride by using a Lewis acid-mediated [4++2] polar cycloaddition with substituted cyclopentenes as a key step.

ChemInform Abstract: A Polar Cycloaddition of 2-Thianaphthylium Ions with 1,3-Dienes and Some Properties of the Cycloadducts.

2-Thianaphthylium ions (1) underwent a polar cycloaddition with 1,3-dienes to afford benzo-fused bicyclic sulfonium salts (2) bearing sulfur atom at bridge-head in excellent yields. The cycloadducts underwent retro-addition reaction to generate the cation (1), which was easily trapped with other diene. Reaction of the adduct (2d) with several nucleophiles caused the ring-opening of (2d) to afford 1-allyl (6) and 1-homoallyl substituted 2-thiochromenes (7) in good yields.

ChemInform Abstract: Cascade Heterocyclization in the Reaction of Tetrafluorobenzobarrelene with 3‐Methoxycarbonyl‐2‐pyridinesulfenyl Chloride.

In recent years, we have developed a new approach to the synthesis of sulfur and nitrogen containing hetero cycles based on the polar cycloaddition of hetarenesulfenyl chlorides HetSCl to alkenes, dienes, and acetylenes accompanied by the ring closure through the nitrogen atom of the HetS fragment.1—6 In particular, it was found that the reactions of 2 pyridinesulfenyl chlorides con taining substituents in the pyridine moiety even with rather readily transformable bicyclic olefins, such as norbornene3 and norbornadiene,6 afford exclusively cycloaddition products with retention of the carbon skeleton of the starting unsaturated compound. With the aim of extend ing the synthetic scope of this approach, in the present study we examined the possibility of performing the tandem rearrangement—cyclization reaction with the use of readily available tetrafluorobenzobarrelene (1)7,8 as the model substrate. The choice of diene 1 was determined by the fact that its reactions with various electrophilic reagents, including sulfenylating agents, involve cascade skeletal rearrangements.8—10

Cyclization of ethyl endo-5-norbornene-2-carboxylate with hetarene sulfenyl chlorides

Cyclization of ethyl endo-5-norbornene-2-carboxylate with 1,3-benzothiazole-2-sulfenyl and 3-methoxycarbonylpyridine-2-sulfenyl chlorides follows two directions, namely, electophilic lactonization of unsaturated ester or polar cycloaddition of sulfenylating reagent to the multiple bond accompanied by ring closure by the nitrogen atom of the thiohetaryl fragment.

Theoretical explanation of the regioselectivity of polar cycloaddition reactions between furan derivatives and Danishefsky’s diene

The regioselectivity for a series of experimentally studied Diels–Alder reactions between furan derivatives and Danishefsky’s diene has been rationalized within the framework of local DFT-based descriptors (i.e. electrophilicity and nucleophilicity indexes). The importance of the solvent in the calculations has been studied. It has been shown that the relative trend of an atomic center to behave as an electrophile is affected by the medium (gas phase or benzene solution) and the basis set used in the calculation of the reactivity descriptors. The local electrophilicity ( ω k ) and nucleophilicity ( N k ) indexes properly account for the observed regioselectivity only when B3LYP/LANL2DZ and HF/LANL2DZ levels of theory have been used.

ChemInform Abstract: Synthesis of Condensed Sulfur‐ and Nitrogen‐Containing Heterocycles via Polar Cycloaddition of Hetarene Sulfenyl Chlorides to a C—C Multiple Bond.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Toward an Understanding of the Unexpected Regioselective Hetero-Diels−Alder Reactions of Asymmetric Tetrazines with Electron-Rich Ethylenes: A DFT Study

The regioselective hetero-Diels-Alder (HDA) reaction of asymmetric tetrazines (TTZs) with electron-rich (ER) ethylenes has been studied with use of DFT methods at the B3LYP/6-31G* level of theory. The reaction is a domino process that comprises three consecutive reactions: (i) a HDA reaction between the TTZ and the ER ethylene; (ii) a retro-Diels-Alder reaction with loss of nitrogen; and (iii) a beta-hydrogen elimination with formation of the final pyridazines. The first polar HDA reaction, which is associated to the nucleophilic attack of the ER ethylene to the electrophilically activated TTZ, is the rate and regioselectivity determining step of the domino process. The unexpected regioselectivity of these HDA reactions is explained within the polar cycloaddition model by using the conceptual DFT. Although the nucleophilic attack of the ER ethylene over the para position relative to the methylsulfinyl substituent could favor the charge transfer, it is energetically more unfavorable because it diminishes the electron density at the electronegative TTZ core.

Cascade heterocyclization in the reaction of tetrafluorobenzobarrelene with 3-methoxycarbonyl-2-pyridinesulfenyl chloride

In recent years, we have developed a new approach to the synthesis of sulfur and nitrogen containing hetero cycles based on the polar cycloaddition of hetarenesulfenyl chlorides HetSCl to alkenes, dienes, and acetylenes accompanied by the ring closure through the nitrogen atom of the HetS fragment.1—6 In particular, it was found that the reactions of 2 pyridinesulfenyl chlorides con taining substituents in the pyridine moiety even with rather readily transformable bicyclic olefins, such as norbornene3 and norbornadiene,6 afford exclusively cycloaddition products with retention of the carbon skeleton of the starting unsaturated compound. With the aim of extend ing the synthetic scope of this approach, in the present study we examined the possibility of performing the tandem rearrangement—cyclization reaction with the use of readily available tetrafluorobenzobarrelene (1)7,8 as the model substrate. The choice of diene 1 was determined by the fact that its reactions with various electrophilic reagents, including sulfenylating agents, involve cascade skeletal rearrangements.8—10

Synthesis of condensed sulfur- and nitrogen-containing heterocycles via polar cycloaddition of hetarene sulfenyl chlorides to a C–C multiple bond

The reactions of HetSCl, where Het = 4,6-dimethyl-2-pyrimidyl, 3-methoxycarbonyl-2-pyridyl, 1,3-benzothiazol-2-yl and 8-quinolyl, with a carbon–carbon multiple bond in the LiClO4–MeNO2 system lead to the formation of products of polar cycloaddition of sulfur-containing electrophile with ring closure by the nitrogen atom of the HetS fragment.