Aromatic glyoxalimines in criss-cross cycloaddition reactions

Aromatic 1,4-diazabuta-1,3-dienes in glacial acetic acid with thiocyanates produce via criss-cross cycloaddition reactions the corresponding perhydroimidazo[4,5-d]imidazole-2,5-dithiones. When a mixture of thiocyanate and cyanate in a proper ratio was reacted together, nonsymmetrical 5-thioxo-perhydroimidazo[4,5-d]imidazole-2-ones were isolated. With cyanates substituted aromatic 1,4-diazabuta-1,3-dienes afforded product of acetic acid addition to primary formed 1,3-dipole intermediate 5-(4-substituted phenylamino)-3-(4-substituted phenyl)-2-oxoimidazolidin-4-yl acetate.     

Trifluoromethyl-p-tolyldiazomethane in 1,3-dipolar cycloaddition reactions

Trifluoromethyl-p-tolyldiazomethane (I) forms [3+2]-cycloadducts with activated alkenes and alkynes. The products of these regiospecific reactions are substituted pyrazolines (II)–(VI) and pyrazoles (VIII)–(X). Reaction of (I) with fumarates, trifluoropyruvates and allyl chloride is accompanied by elimination of N₂ and formation of a 1,2-bis(trifluoromethyl)stilbene. The results obtained indicate that (I) enters only the HOMO-controlled 1,3-dipolar addition reactions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1589–1593, July, 1991.     

A frontier molecular orbital treatment of fulvene cycloadditions : Molecular orbital calculations and photoelectron spectra of substituted fulvenes

MO calculations have been carried out on substituted fulvenes by several semiempirical methods. The results of these calculations are compared with those by other methods, and with photoelectron spectroscopic data obtained here for several substituted fulvenes. Predictions about the periselectivity ([6+4] or [4+2]) of fulvene cycloadditions with dienes, 1,3-dipoles, and ketenes are made and compared with experimental data, where available.     

Frontier orbital controlled cycloaddition of 2-azapentalenes

It is shown that cycloadditions of 1,3-bis (dimethylamino) pentalenes and their 2-aza-analogues with activated alkines are frontier orbital controlled whereas protonation is charge controlled.     

Some cycloaddition reactions of halomethylenecyclopropanes

Bromo-,chloro- and ethoxymethylenecyclopropane 3–5 undergo head to head dimerzations at 185–195° to give the corresponding 7,8-disubtituted dispiro[2.0.2.2]octanes 6–8 in high yields. Chloromethylenecyclopropane 4 undergoes cross cycloaddition reactions with near equimolar amounts of 3 and 5 to give about 50% of the corresponding mixed 7,8-disubstituted dispiro[2.0.2.2]octanes together with equal parts of 6 and 7 or 6 and 8. Bromo- and choromethylenecyclopropane also undergo similar cross cycloaddition reactions with methelene-cyclopropane to give the 7-halodispiro[2.0.2.2]octanes, but in relatively poor yields. At 190°, 4 reacts with 1,3-cyclopentadiene, furan, and 1,3-cyclohexadiene to give the products of (2+4) cycloaddition 12–14. With 2,3-dimethyl-1,3-butadiene at 190° ,4 gives the unusual products 18–20 in yields of 35%, 8% and 13%, respectively, and with acryloionitrile 4 gives exclusively 21, the product of (2+2) cycloaddition. Relative reactivities of 4 with furan, 2,3-dimethyl-1,3-butadiene, 1,3-cyclohexadiene, acrylonitrile and 1,3-cyclopentadiene were estimated as 1:2.5:2.5:4:and 50,respectively.     

Asymmetric polymerization via cycloaddition reactions

The reaction of N‐phthaloyl‐L ‐leucine acid chloride (1) with isoeugenol (2) was carried out in chloroform, and novel optically active isoeugenol ester derivative 3 as a chiral monomer was obtained in high yield. Compound 3 was characterized by ¹H‐NMR, IR, and mass and elemental analysis and then was used for the preparation of model compound 5 and polymerization reactions. 4‐Phenyl‐1,2,4‐triazoline‐3,5‐dione, PhTD (4), was allowed to react with compound 3. The reaction is very fast and gives only one diastereomer of 5 via Diels–Alder and ene pathways in quantitative yield. In order to explain this diastereoselectivity, a nonconcerted two‐step mechanism involving benzylic cation (BC) and aziridinium (AI) have been proposed for the Diels–Alder and ene reactions, respectively. The polymerization reactions of novel monomer 3 with bis(triazolinedione)s [bis(p‐3,5‐dioxo‐1,2,4‐triazolin‐4‐ylphenyl)methane (8) and 1,6‐bis(3,5‐dioxo‐1,2,4‐triazolin‐4‐yl)hexane] (9)] were performed in N,N‐dimethylacetamide (DMAc) at room temperature. The reactions are exothermic, fast, and gave novel optically active polymers 10 and 11 via repetitive Diels–Alder–ene polyaddition reactions. These polymers have inherent viscosities in a range about 0.18–0.22 dL/g. Some physical properties and structural characterizations of these new polymers have been studied and are reported. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1211–1219, 1999     

Deviating behaviour of bromocarbethoxycarbene in cycloaddition reactions

The effect of Me substituents at alkenes 4 on the rates and activation parameters of cycloaddition reactions of bromocarbethoxycarbene (3) is very small. This carbene does not fit into the general equation (b) and the isoselective relationship (c) of dihalocarbenes. The deviating behaviour can be explained by a diffusion controlled reaction rate of bromocarbethoxycarbene.     

Regioselectivity in dipolar cycloaddition reactions of N-phenylcinnamonitrilimine

The regioselectivity of the cycloadditions of α,β-unsaturated nitrilimine derived from N-phenylcinnamo-hydrazidoyl chloride 2 to C = Se, C = S and C = C double bonds of the resonance stabilized selenocyanate and thiocyanate anions, enol tautomer of dibenzoylmethane and benzalacetophenone was investigated. The results indicate that the reactions studied are dipole-LUMO-dipolarophile-HOMO controlled and that the larger orbital coefficient in the LUMO of N-phenylcinnamonitrilimine is on the carbon atom bearing the styryl group. The structures of the cycloadducts were assigned and confirmed on the basis of their elemental analyses and spectra.     

Electronic effects in 1,3-dipolar cycloaddition reactions of N-alkyl and N-benzyl nitrones with dipolarophiles

1,3-Dipolar cycloadditions afforded fast access to isoxazolidines bearing N-alkyl or N-benzyl substituents. The electronic properties of the substituents in the nitrones define the activity of the dipoles and modulate diastereoselectivity in the non-catalyzed reactions. Using a chiral one-point binding ruthenium Lewis acid catalyst, products were obtained in good yields and with excellent regio-, diastereo-, and enantioselectivity.     

Intramolecular cycloaddition reactions involving nitrile sulphides

ortho-(Phenylpropioloxy)benzonitrile sulphide, generated in situ by thermal decarboxylation of the oxathiazolone (1), undergoes intramolecular 1,3-dipolar cycloaddition forming the chromenoisothiazole (4a); ortho-cinnamoylbenzonitrile sulphides also yield (4), together with nitrile, chromenoquinoline and amino-chromene by-products.     

Chiral nitrone reagents for cycloaddition reactions

The preparation and cycloaddition reactions of new imidazoline nitrones are described. The imidazo[1,2‐b]isoxazole alkene cycloadducts are formed via an exo approach. An example has been tranformed into a pyrrolo[1,2‐a]imidazole as a prelude to a new pyrrolidine synthesis.     

Cyclopropenes and methylenecyclopropanes in 1,3-dipolar cycloaddition reactions

The review considers the main results of the cycloaddition reactions involving cyclopropenes and methylenecyclopropanes, the compounds bearing strained three-membered rings and, respectively, endo- and exocyclic double bonds. The main attention is focused on the reactions of these compounds with 1,3-dipoles (nitrones, azomethine imines, azomethine ylides, carbonyl ylides, etc.), which gave complex heterocyclic systems with high regio- and stereoselectivity.

     

Synthesis of spiropyrrolidines: 1,3‐dipolar cycloaddition reactions of an azomethine ylide to unusual dipolarophiles; a molecular orbital study of the cycloaddition reaction

A simple and efficient method for the synthesis of novel spiropyrrolidines has been accomplished by regioselective 1,3‐dipolar cycloaddition reactions of an azomethine ylide generated by thermal‐ring opening of cis‐1‐cyclohexyl‐2‐phenyl‐3‐benzoyl aziridine with various (E)‐3‐arylidene‐4‐chromanones. The synthesis proceeds in good yield to afford novel spiropyrrolidines, 1‐cyclohexyl‐2‐phenyl‐3‐aryl‐5‐benzoylpyrrolidine‐spiro‐[4.3′]4′‐chromanones. The X‐ray crystal structure analysis of one of the products confirms its structure. Molecular orbital calculations were performed to investigate the regioselectivity of the cycloaddition process. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 500–507, 1999     

Characteristics of the two frontier orbital interactions in the Diels-Alder cycloaddition

Two electron-deficient dienes were reacted with a series of twelve electron-poor and electron-rich dienophiles to give, in some cases, the corresponding Diels-Alder adducts. Clear differences in the roles played by the two frontier orbital interactions emerged. It was demonstrated that in the case of normal Diels-Alder cycloadditions, the FMO theory could predict the relative reactivities between dienophiles, while in the case of inverse-electron demand Diels-Alder reactions, it could not. It was shown that the dissymmetry in electron-rich dienophiles increases their reactivities.     

Natural orbital Fukui function and application in understanding cycloaddition reaction mechanisms

A new condensed form of the Fukui function, the natural orbital Fukui function (NOFF), is proposed and derived from natural bond orbital occupancy. It is defined as the change in natural bond orbital occupancy upon electronic perturbation (electron addition to, or depletion from, a molecular system). Applying NOFF to a series of cycloaddition reactions (e.g., [4 + 2] and [2 + 1] cycloadditions) illustrates the effectiveness of the concept in interpreting bond breakage and formation mechanisms.