Haval-Argade contrathermodynamic rearrangement of alkylidenesuccinimides to alkylmaleimides via the corresponding isoimides: a general approach to alkyl and dialkyl substituted maleimides

A simple and efficient access to alkyl and dialkyl substituted maleimides has been demonstrated via the new contrathermodynamic rearrangement of (E)-alkylidenesuccinimides to alkylmaleimides. The (E)-alkylidenesuccinimides obtained from the Wittig-condensation of N-arylmaleimide with aliphatic aldehydes on regioselective hydrolysis furnished the corresponding (E)-alkylidenesuccinanilic acids in 95-98% yields. The β-alkylidenesuccinanilic acids on treatment with cyanuric chloride in the presence of triethylamine gave the corresponding β-alkylisomaleimides in 78-80% yields via the β-alkylideneisosuccinimides with the exocyclic to endocyclic carbon-carbon double bond migration. The kinetically controlled products alkylisomaleimides in refluxing acetic acid furnished the thermodynamically controlled alkylmaleimides in 98% yield. The Wittig condensation of alkyl substituted isomaleimides/maleimides with aliphatic aldehydes gave the desired dialkyl substituted maleimides in high yields. A conversion of α-methylenesuccinanilic acids to α-methylisomaleimides has also been described, with 90% yield.     

Peroxide-initiated grafting of maleimides onto hydrocarbon substrates

The grafting of N-phenethyl-maleimide (1) onto squalane and eicosane was investigated. As reference substances for spectroscopical investigations homopolymer, N-phenethyl-succinimide (2), t-butyl-(4) and cyclohexyl-N-phenethyl-succinimide (6) were synthesized. The grafting reactions were carried out at 150 °C in 1,2-dichlorobenzene with Luperox 130 as initiator (molar ratio hydrocarbon substrate:1:initiator = 10:1:0.2). Two fractions of graft products were isolated and analysed by ¹H NMR, ¹³C NMR, FTIR and UV spectroscopy, SEC and MALDI-TOF MS to determine the average number of grafted residues per substrate molecule and to elucidate the structure of the grafts and the grafting sites. Overall grafting yields were found to be >90%. Only a small percentage of the total amount of substrate was grafted (2-3%). First fraction of both oligomers (approx. 25 wt%) showed to be a mixture of homopolymers (average degree of polymerization 6) and graft products (approx. 1:3), the latter containing mainly long-chain grafts with an average chain length of 7. The major fraction of graft products contained predominantly single units. As an average number of units per substrate molecule very similar results were obtained for eicosane and squalane (n = ∼ 3). In the case of squalane single units were found to be linked mainly to tertiary carbon atoms, long chain grafts mainly to secondary C-atoms. Apart from the homopolymers resulting from radical transfer, homopolymers terminated with methyl groups resulting from secondary radicals formed by the decomposition of Luperox were also observed. Homopolymers as well as graft products were found to contain small amounts of maleimide groups. The results suggest that as in the mechanism proposed for maleic anhydride, both inter- and intramolecular hydrogen abstraction occurs as part of the chain process. Termination proceeds mainly by hydrogen transfer and also by disproportionation, to a lesser extent. The formation of long chain grafts on tertiary carbons seems to be sterically hindered.     

Convenient construction of spiro[indoline-3,5'-pyrrolo[3,4-c]carbazole] and spiro[indene-2,5'-pyrrolo[3,4-c]carbazole] via acid-catalyzed Diels-Alder reaction

p-TsOH catalyzed Diels-Alder reaction of 3-(indol-3-yl)maleimides with 3-phenacylideneoxindoles in toluene at 80 °C for two hours afforded cis/trans isomers of 3a',4′,6′,10c'-tetrahydrospiro[indoline-3,5′-pyrrolo[3,4-c]carbazoles] in nearly comparable yields, which could be easily converted to the corresponding 4′,6′-dihydrospiro[indoline-3,5′-pyrrolo[3,4-c]carbazole] in high yields and with high diastereoselectivity by further DDQ oxidation. Additionally, the similar reaction of 3-(indol-3-yl)maleimides with 2-arylidene-1,3-indanediones in toluene 80 °C and sequential DDQ oxidation afforded functionalized dihydrospiro[indene-2,5′-pyrrolo[3,4-c]carbazoles] as major products.     

Convergent integration of three self-sorting domino sequences: three-component direct synthesis of 3-methylthio-4-aryl-maleimides from methyl ketones with acetonitrile and DMSO

An I₂-promoted three-component coupling reaction was described for the construction of 3-(methylthio)-4-aryl-1H-pyrrole-2,5-diones from methyl ketones with acetonitrile and DMSO. This transformation involved the in situ generation and application of α-ketoimides. Furthermore, DMSO was converted to DMS in situ, which subsequently served as a methylthiolation reagent in the reaction. To the best of our knowledge, this protocol provided the first known example of convergent integration of three self-sorting domino sequences.     

NMR Studies of Hindered Rotation and Magnetic Anisotropy: The Diels–Alder Adducts of Phencyclone with N‐Phenylmaleimide and N‐(2‐Trifluoromethylphenyl)maleimide. Ab Initio Calculations for Optimized Structures

Abstract

N‐Phenylmaleimide, 2, and N‐(2‐trifluoromethylphenyl)maleimide, 3, were separately added to phencyclone, 1, to yield the corresponding phencyclone Diels–Alder adducts, 4 and 5. The resulting adducts (and some precursors) have been characterized by one‐ and two‐dimensional ¹H and ¹³C NMR at 300 and 75 MHz, and by ¹⁹F NMR at 282 MHz, at ambient temperatures. The NMR data are consistent, for both adducts, with: (a) hindered rotation of the bridgehead unsubstituted phenyl groups about the C(sp²)–C(sp³) bonds, based on slow exchange limit (SEL) spectra and (b) endo adduct configuration based on magnetic anisotropic effects in the ¹H NMR. The NMR spectra of the phencyclone adduct, 4, of N‐phenylmaleimide, indicate free rotation on the NMR timescales (fast exchange limit, FEL spectra) about the N‐phenyl bond. The spectra for the adduct, 5, of N‐(2‐trifluoromethylphenyl)maleimide are interpreted as consistent with SEL regimes, for the N‐aryl rotations, with a single rotamer present in which the trifluoromethyl group is directed “out of” the adduct cavity, and away from the phenanthrenoid moiety. This conclusion is based, in part, on NMR data suggesting the apparent slow N‐aryl bond rotation in a pair of atropisomers corresponding to the acetic acid addition products from the N‐(2‐trifluoromethylphenyl)maleimide. Evidence of magnetic anisotropic effects due to the phenanthrenoid moiety and proximal carbonyls is discussed. ¹H, ¹³C, and ¹⁹F assignments are presented and interpreted. Molecular modeling calculations at the Hartree–Fock level, 6‐31G* basis set, were performed to provide geometry optimizations for energy‐minimized structures of selected compounds.     

Stable but chimeric antiaromatic 1H-azirines? A threefold reinvestigation

Three different reports on the syntheses of isolable 1H-azirines 6, 15, and 21 were reinvestigated. Instead of the claimed heterocyclic product 6, the isomeric thiazole derivative 7 has been isolated now with nearly identical yield. In the case of the asserted bicyclic 1H-azirine 15, the corrected structure includes the isomeric 3-aminomaleimide moiety of 18. A mechanism to explain the formation of this substance is suggested. The isolation of the antiaromatic compound 21 has also to be rejected. Thus, 1H-azirines keep their classification as very elusive high-energy intermediates.