Intermolecular [4+3] Cycloaddition of Cyclic Oxyallyl

The[4+3]cycloaddihonreachonofatlyliCcationsanddienesisavodemeIhalfortheconstwhonofseven-memberedrings1.AkCyvariantofemPlOyingacyclicoxyalll,i.e.,anoxyallylembeinring,wouldPrOvidCaconvenientroutetofunctiotaledmdri-eddsyClesandheteIDCycles.Inaddihon,theketobridgeinthecycloadductwouldbeusefulnotonlyinProvthegasultablefUnchonalityforfurtherebohonbutalsoinrigmpingthefiechemedium-edring.Chaandhisco-workershaveemployedthesaPPrOaChtOthesynthesisofnandProductS2.AtpesenLonlyafewexamplesofthisre…     

Rhodium-Catalyzed [2+1+2+1] Cycloaddition of Benzoic Acids with Diynes through Decarboxylation and C≡C Triple Bond Cleavage

It has been established that an electron-deficient cyclopentadienyl rhodium(III) (Cp^ERh^III) complex catalyzes the oxidative and decarboxylative [2+1+2+1] cycloaddition of benzoic acids with diynes through C≡C triple bond cleavage, leading to fused naphthalenes. This cyclotrimerization is initiated by directed ortho C−H bond cleavage of a benzoic acid, and the subsequent regioselective alkyne insertion and decarboxylation produce a five-membered rhodacycle. The electron-deficient nature of the Cp^ERh^III complex promotes reductive elimination giving a cyclobutadiene–rhodium(I) complex rather than the second intermolecular alkyne insertion. The oxidative addition of the thus generated cyclobutadiene to rhodium(I) (formal C≡C triple bond cleavage) followed by the second intramolecular alkyne insertion and reductive elimination give the corresponding [2+1+2+1] cycloaddition product. The synthetic utility of the present [2+1+2+1] cycloaddition was demonstrated in the facile synthesis of a donor–acceptor [5]helicene and a hemi-hexabenzocoronene by a combination with the chemoselective Scholl reaction.     

Brønsted acid TfOH-mediated [3 + 2] cycloaddition reactions of diarylvinylidenecyclopropanes with nitriles

Diarylvinylidenecyclopropanes undergo a [3 + 2] cycloaddition reaction with MeCN in the presence of Br?nsted acid TfOH to give the corresponding 3,4-dihydro-2 H-pyrrole derivatives 2 in moderate to excellent yields under reflux within a short time. As for the diarylvinylidenecyclopropane substrate containing a strongly electron-donating methoxy group on the benzene ring, the reaction leads to the formation of a different type of 3,4-dihydro-2 H-pyrrole derivatives 4 under the same conditions.     

Thermolysis and [3+2]‐Cycloaddition Reactions of 2,3‐Diferrocenyl‐ and 2,3,‐Diruthenocenylcyclopropenones

Abstract

2,3‐Diferrocenyl‐ and 2,3‐diruthenocenylcyclopropenone undergo thermolysis at ～180°C with opening of the small ring via ketenocarbenes. Intramolecular transformation of the latter occurs with elimination of CO to yield dimetallocenylacetylenes. Alternatively, they enter into 1,3‐dipolar cycloaddition reactions with C≡C or C?C multiple bonds to give cyclopentadienone or cyclopentenone derivatives, respectively.     

Stereoselective synthesis of 2-substituted 3-azabicyclo[3.2.0]heptan-2-ones by [2+2]-cycloaddition of N-allyl-β-N-keteniminium salts derived from (R)-vinylglycinol

A stereoselective synthesis of (1R,2R,5S)-2-benzyloxymethyl-3-azabicyclo[3.2.0]heptan-2-one was achieved, by intramolecular [2+2]-cycloaddition of (R)-vinylglycinol-derived N-allyl-β-N-keteniminium salts, with high facial diastereoselection. The regio- and stereochemical courses have been qualitatively investigated by Molecular Mechanics calculations.     

Oxidation of Enones for Regioselective [3+2] Cycloaddition through γ-Enone Radical Intermediates

Herein, an oxidization reaction of enones with a Cu^II complex that leads to a new type of regioselective [3+2] cycloaddition is reported. Highly functionalized cyclopentenes and spirocyclic compounds are obtained in moderate-to-good yields. This cycloaddition reaction occurred through the formation of γ-enone radicals, providing a rarely explored reactivity pattern for enones.     

[3 + 2] Cycloaddition of Diazomethane Derivatives to Perfluoro-2-phosphapropene

Perfluoro-2-phosphapropene ( 1 ) reacts with diazo compounds R(H)C=N₂ (R = H ( 2 a ), Ph ( 2 b ), CO₂Et ( 2 c ), Me₃Si ( 2 d )) at low temperatures regioselectively yielding via 1,3-H shift the novel 1,2,3-diazaphospholes 4 a – d . The mesomerically stabilized compounds 4 b and 4 c were characterized by NMR spectroscopy and single crystal X-ray diffraction studies. Using diphenyldiazomethane 5 as partner for 1 , the cycloaddition is spontaneously followed by N₂ elimination to give the crystalline phosphirane derivative 7 . The analogous reaction of 1 with 9-diazofluorene 9 unexpectedly leads to the so-far unknown 1,2-diphosphinane compound 11 . Quantum chemical calculations for the gas phase on DFT and RHF level prove that for both the perhydro- and the perfluoro-2-phosphapropene the [3 + 2]-cycloaddition is kinetically determined and that, due to high stability of the products, the thermodynamic equilibrium with the slightly more stable isomers is not accessible.     

Application of Hantzsch Dihydropyridine in Copper-Catalyzed [3 + 2] Cycloaddition of Terminal Alkynes with Azides

2,6-Dimethyl-3,5-bis(ethoxycarbonyl)-1,4-dihydropyridine (dihydropyridine Hantzsch ester, DHPHE) and CuSO₄ · 5H₂O efficiently accelerated azide–alkyne cycloaddition reactions of both aliphatic and aromatic substrates and gave 1,4-disubstituted 1,2,3-triazoles as the only isomer in good to excellent yields at room temperature with 1 mol% of CuSO₄ · 5H₂O/DHPHE (1:1 in molar ratio). The reaction could be carried out smoothly in methanol in air with high efficiency. DHPHE may play multiple important roles in the reaction: a reducing reagent to generate the catalytic center copper(I) from CuSO₄, a base to help form the intermediate acetylide, and a ligand to stabilize the catalytic copper(I) species via coordination after being transformed to pyridine derivative.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

Catalytic Formal [2π+2σ] Cycloaddition of Aldehydes with Bicyclobutanes: Expedient Access to Polysubstituted 2-Oxabicyclo[2.1.1]hexanes

Synthesis of bicyclic scaffolds has attracted tremendous attention because they are playing an important role as saturated bioisosteres of benzenoids in modern drug discovery. Here, we report a BF₃-catalyzed [2π+2σ] cycloaddition of aldehydes with bicyclo[1.1.0]butanes (BCBs) to access polysubstituted 2-oxabicyclo[2.1.1]hexanes. A new kind of BCB containing an acyl pyrazole group was invented, which not only significantly facilitates the reactions, but can also serve as a handle for diverse downstream transformations. Furthermore, aryl and vinyl epoxides can also be utilized as substrates which undergo cycloaddition with BCBs after in situ rearrangement to aldehydes. We anticipate that our results will promote access to challenging sp³-rich bicyclic frameworks and the exploration of BCB-based cycloaddition chemistry.     

Rhodium-catalyzed synthesis of 2,3 – Disubstituted N-methoxy pyrroles and furans via [3+2] cycloaddition between metal carbenoids and activated olefins

For the first time, we report the synthesis of 2-substituted N-alkoxy pyrrole 3-carboxylate and furan 3-carboxylate via Rh-catalyzed [3+2] cycloaddition between α-diazo oxime ether or α-diazo carbonyl compounds with vinyl equivalents in a one-pot process. We have demonstrated ethyl vinyl ether as well as vinyl acetate as vinyl equivalents and both were found to give excellent yields. We have also demonstrated the synthesis of N-alkoxy dihydropyrrole derivatives by carrying out the reaction at low temperature.     

Regioselective [3+2] cycloaddition of nitrile oxides to 1Н-pyrrole-2,3-diones: synthesis of spiro[pyrroledioxazoles]

Chemistry of Heterocyclic Compounds - 1,3-Dipolar cycloaddition of 1H-pyrrole-2,3-diones to nitrile oxides generated in situ from N-hydroxybenzimidoyl chlorides by the action of triethylamine...     

Regio- and stereoselective synthesis of 3- and 5-(C-glycosyl)-4-nitroisoxazolidines by nitrone–nitroalkene [3+2] cycloaddition reactions

Cycloaddition reactions of nitrones, including sugar nitrones, with nitroalkenes, including sugar nitroolefins, led with complete regioselectivity and stereospecificity to 4,5-trans-4-nitroisoxazolidines in 51–78% global yields. The endo/exo stereoselectivity depends on the type of sugar derivative used. As expected, the best π-diastereofacial selectivity was observed when both partners were sugar derivatives. Isomerisation of the first formed diastereomers by the action of silica gel was observed in some cases. Absolute configurations for two crystalline products were assigned by X-ray diffraction methods.     

Synthesis of 4-substituted 3-oxabicyclo[3.1.0]hexan-2-one

Cyclopropanedicarboxylic acid anhydride can be converted to 4-substituted 3-oxabicyclo-[3.1.0]hexan-2-one by reaction with Grignard reagents in ether or tetrahydrofuran solution.     

Palladium-Catalyzed [3+2] and [2+2+2] Annulations of 4-Iodo-2-quinolones with Activated Alkynes through Selective C−H Activation

The palladium-catalyzed reaction of 4-iodo-2-quinolones with activated alkynes was investigated. Cyclopenta[de]quinoline-2(1 H)-ones and/or phenanthridine-6(5 H)-ones were obtained through [3+2] annulation involving aromatic C−H activation or [2+2+2] annulation involving vinylic C−H activation, respectively. Reasonable mechanisms for the formation of these annulation products have been proposed based on density functional theory calculations.     

Synthesis of androsteno[17,16-d]pyrazoles and androsteno[17,16-d]-2′-pyrazolines with pyrazolo[3,4-d]pyrimidine fragments

Russian Chemical Bulletin - Reactions of pyrazolo[3,4-d]pyrimidine-containing hydrazines with pregnenolone derivatives were studied. The reaction of...     

Construction of the Core of Pseudolaric Acid A and Mechanistic Studies on Intramolecular [4+3] Cycloaddition

Pseudolaric acid A (1), which exhibits antifungal activity, cytotoxicity against several tumor cell lines in vitro, as well as contraceptive effects in mice, is a diterpenoid compound isolated from Pseudolarix Kaemferi1. The unusual structural feature in this molecule is a trans arrangement of the lactone and acetoxy group at the fused junction of 5, 7-fused ring skeleton bearing four contiguous stereogenic centers. The synthetic challenges posed by these structural elements in a rather compa…     

Asymmetric Induction in [3 + 2] Dipolar Cycloaddition Reactions of Nitrile Oxides with Chiral (α-Oxyallyl)silanes

The dipolar cycloaddition reactions of(α-oxyallyl)silanes 12a-g with 2,2-dimethylpropanenitrile oxide and benzonitrile oxide have been studied. Mixtures of anti (14a-g and 16a-g) and syn (15a-g and 17a-g) Δ²-isoxazolines are formed. The direction and magnitude of asymmetric induction depends on the allylie oxygen substituent: a free hydroxy provides a modest excess of the syn diastereomer, a silyl ether shows good selectivity for the anti diastereomer, and various acyl derivatives show low diastereoselectivity. The significance of these results is discussed in terms of two current models for asymmetric induction.     

Unexpected Direct Synthesis of N-Vinyl Amides through Vinyl Azide–Enolate [3+2] Cycloaddition

The unexpected synthesis of industrially important N-vinyl amides directly from aldehydes and α,β-unsaturated N-vinyl amides from esters is reported. This reaction probably proceeds through an initial [3+2] azide–enolate cycloaddition involving a vinyl azide generated in situ. A survey of the reaction scope and preliminary mechanistic findings supported by quantum computational analysis are reported, with implications for the future development of atom-efficient amide synthesis. Intriguingly, this study suggests that (cautious) reevaluation of azidoethene as a synthetic reagent may be warranted.