Cycloaddition Partners Research Articles

Low‐lying stepwise paths for ethylene 1,3‐dipolar cycloadditions: A DFT study

AbstractEthylene reacts with 1,3‐dipoles such as diazomethane, nitrile oxide, and nitrone to give a single adduct and the potential energy surfaces of these reactions were completely surveyed with Density Functional Theory at the B3LYP/6‐31G(d) level; B3LYP/6‐311+G(d,p), QCISD/6‐31G(d) level calculations were performed for comparison. These reactions were found to have one concerted and four stepwise paths and all of them were thoroughly examined. Calculations show that anti and syn approaches in the stepwise paths merge at one point in the potential energy surface and the stepwise processes (i.e., through syn transition states) are low‐lying and concerted paths that are in close competition with them. A closer examination of the computed barriers of the reactions of ethylene with the above dipoles, cyclopentadiene, 1,3‐butadiene, and allyl anion reveals that there is a mechanistic cross‐over from concerted to stepwise path. While the neutral cycloaddition partners prefer a concerted path, the charged partners strongly favor a stepwise path. The dipoles have both concerted and stepwise (syn) paths in close competition. Such a mechanistic cross‐over has been induced by the polar influence of the charged species and this change‐over in mechanism could not be observed with allene cycloadditions with the same set of partners because allene is strongly biased towards the stepwise mechanism. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

Simultaneously Electrogenerated Cycloaddition Partners for Regiospecific Inverse‐Electron‐Demand Diels—Alder Reactions: A Route for Polyfunctionalized 1,4‐Benzoxazine Derivatives.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Simultaneously electrogenerated cycloaddition partners for regiospecific inverse-electron-demand Diels-Alder reactions: a route for polyfunctionalized 1,4-benzoxazine derivatives.

A multistep one-pot electrochemical synthesis of a variety of complex 2-alkylamino-1,4-benzoxazine derivatives is described. The reactions are regiospecific and diastereospecific in the case of heterocyclic annulation. This cascade sequence, wherein both cycloaddition partners are generated in situ, at room temperature, under metal-free conditions, allows the inverse-electron-demand Diels-Alder reaction of an o-iminoquinone diene and a secondary alkylenamine dienophile, two chemically nonaccessible unstable entities. To increase the molecular diversity, a variant in which the enamine is separately prepared completes the aforementioned procedure. The extension of this reaction should be useful to generate libraries of heterocycles.

Solid-phase synthesis of polysubstituted piperidines by imino-Diels-Alder cycloaddition of 2-amino-1,3-butadienes with solid-supported imines.

[reaction: see text] The solid-phase imino-Diels-Alder reaction of 2-amino-1,3-butadienes with solid-supported imines is described. The reaction furnishes 4-piperidones and 4-aminopiperidines with high diastereoselectivity and with very good yields and purity after the release from the solid support. The possibility of introducing variations in both cycloaddition partners gives rise to substituted piperidines with up to five elements of diversity.

NIR chromophores from small acetylenic building blocks: a Diels–Alder approach to octaalkynylphthalocyanines

Two new routes to cross-conjugated 3,4-dimethylenehexa-1,5-diynes, both starting from dialkynyl 1,2-diones, have been devised. Whereas triisopropylsilyl-protected diketones could be diolefinated in a bis-Wittig reaction with methylenetriphenylphosphorane, their aryl-terminated congeners had to be subjected to the conditions of the Peterson olefination (trimethylsilylmethylmagnesium chloride and subsequent dehydration of the resulting diol with thionyl chloride). The reactivity of the diethynylbutadienes towards standard dienophiles was found to be low and alternative thermal reactions compete with [4 + 2] cycloadditions. However, dicyanoacetylene was shown to be an effective cycloaddition partner leading, after aromatisation, to the corresponding dicyanodiethynylbenzenes. These were cyclotetramerised with magnesium butanolate in butanol to furnish octaalkynylphthalocyanines, thereby completing a concise, three-step synthesis of these NIR chromophores of relevance to photodynamic forms of therapy.

Total Synthesis of (+)-Aloperine. Use of a Nitrogen-Bound Silicon Tether in an Intramolecular Diels−Alder Reaction

Enantioselective total syntheses of aloperine (1), N-methylaloperine (2), and N-allylaloperine (3) are reported. The central element of the synthetic strategy is an intramolecular Diels−Alder reaction in which the cycloaddends are tethered by a N-silylamine linkage. The total synthesis of 1 proceeds from commercially available 3-hydroxypiperidine hydrochloride (54) and (R)-pipecolinic acid (35) by way of nine isolated and purified intermediates. The synthesis is sufficiently efficient that gram quantities of (+)-aloperine (1) can be readily prepared. Early exploratory studies also introduced a convenient method for tethering cycloaddition partners with a sulfonamide unit to realize the intramolecular Diels−Alder cycloaddition of a vinylsulfonamide: 45 → 46.

ChemInform Abstract: Organophosphorus Compounds. Part 123. Trimethylsilylphosphaacetylene as Cycloaddition Partner for 1,3‐Dipoles.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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.

Synthesis and Diels-Alder reactivity of functionalized aminodienes and bis-dienes

γ-Amino α,β-unsaturated dimethyl acetals are direct precursors of (E)-1-methoxy-2-methylamino-1,3-butadiene and of the corresponding bis-dienes, which are useful partners in cycloadditions.

Generation and cycloaddition reactions of substituted 2-nitro-1,3-dienes

4-Acyloxy-2-substituted-3-nitro-1-butenes have been utilized as convenient precursors of the corresponding 2-nitro-3-substituted-1,3-butadienes which could be easily generated in situ by heating or by treatment with sodium acetate and trapped by suitable partners such as methyl acrylate, cyclopentadiene or ethyl vinyl ether. The expected cycloadducts are regiochemically formed by reaction with methyl acrylate, while the initially formed adducts with cyclopentadiene underwent thermal Cope or hetero-Cope rearrangements leading to the formation of nitro-substituted bicyclic compounds. The thermal rearrangement of the oxazine-N-oxides resulting through hetero Diels-Alder reaction with ethyl vinyl ether as cycloaddition partner led to the formation of 1,2-oxazole-3-propionaldehydes. The wide variety of highly functionalized carbocyclic and heterocyclic compounds generated through the use of these multi-coupling reagents provided useful synthons for the construction of simple and complex natural compounds.

New thione chemistry

Abstract

Sulfones from Mono- and Dithioacetals as Sulfur Chemist'S Tool

Abstract Mainly applied syntheses of sulfones of O,S- and of S,S-acetals are briefly summarized; special types of these compounds represent the corresponding ketene acetals. Characteristic reactions all of these classes of compounds - including α sulfonyl carbanions as nucleophiles, α-substituted vinyl sulfones as Michael-acceptors or as cycloaddition partners, especially with regard to their synthon properties - are discussed.

Exploration of the [3 + 2] Cycloaddition Reaction Between Allylstannanes and α,β-Unsaturated Acyliron Complexes

The reaction between allylstannanes and α,β-unsaturated acyliron complexes has been investigated. Contrary to the behavior of other α,β-unsaturated carbonyl compounds, α,β-unsaturated acyliron complexes react with allylstannanes to produce predominately cyclopentane derivatives with a high degree of stereoselectivity. The initial cycloadducts contain acyliron and trialkylstannyl functionalities, which are readily converted to ester and alcohol groups, respectively, with complete retention of stereochemistry. Transition state models involving a synclinal orientation of reactants have been proposed to explain the observed stereochemistry. Studies of cyclization reactions of 5-hexenylstannanes have also been described. 1. Introduction 2. Why Examine the Reaction Between Allylstannanes and α,β-Unsaturated Acyliron Complexes in the First Place? 3. Optimization of the Reaction Between Allyltributyltin and Acryloyldicarbonyl(η-cyclopentadienyl)iron (2). 4. Will Allyltributyltin React with Other α,β-Unsaturated Acyliron Complexes in the Same Manner? 5. Will Acryloyliron Complex 2 React Similarly with Other Allylic Tributylstannanes? 6. Reactions in which Both Cycloaddition Partners Bear Additional Substituents 7. What Do Other Allylmetal Complexes Do? 8. Development of Methods for Conversion of the Metals to Simpler Functional Groups 9. Development of New C-Sn Bond Cleavage Reactions 10. Assignment of Stereochemistry 11. What Is the Mechanism of the Reaction? 12. How Do We Explain the Observed Stereoselectivity? 13. What's So Great About This Model? 14. Why Do α,β-Unsaturated Acyliron Complexes Behave So Differently from Other α,β-Unsaturated Carbonyl Compounds? 15. How Do We Explain Those Cases Where Open-Chain Products Are Obtained? 16. Summary and Outlook

Reactivity of Tri‐tert‐butylazete

The first kinetically stabilized azete, the title compound 1, is sensitive toward oxidation (→ formation of the dioxetane 2) and undergoes hydrolysis to the β-imino ketone 3. Sterically nondemanding cycloaddition partners such as cyclopentadiene or diazomethane (CH2N2) (→ formation of the adduct 4) attack at C-2/C-3, whereas those with bulky groups such as acetylenedicarboxylate esters or tert-butylphosphaacetylene (PCtBu) (→ formation of the bicyclic compound 5) react at N-1/C-4.

Reactive Derivatives of Aliphatic N‐Sulfinylamines—Alkylation of N‐Sulfinylalkylamines and Bis (tert‐butyl)‐sulfur Diimide

N‐Sulfinylimmonium tetrafluoroborates (3) are valuable reagents and certainly not mere inorganic curiosities; they are readily accessible by alkylation of N‐sulfinylamines (1). Former syntheses of similar salts were much more involved. The salts (3) are very good cycloaddition partners, and also provide a new entry to aminosulfonium salts of type (4). equation image equation image

A New Synthetic Entry to Mono‐, Bis‐, and Tris‐(amino)sulfonium Salts

N‐Sulfinylimmonium tetrafluoroborates (3) are valuable reagents and certainly not mere inorganic curiosities; they are readily accessible by alkylation of N‐sulfinylamines (1). Former syntheses of similar salts were much more involved. The salts (3) are very good cycloaddition partners, and also provide a new entry to aminosulfonium salts of type (4). equation image equation image