Vicarious nucleophilic substitution of hydrogen versus vinylic substitution of halogen in the reactions of carbanions of halomethyl aryl sulfones with dialkyl halofumarates and halomaleates

Reaction of halomethyl aryl sulfone carbanions with dialkyl halofumarates and halomaleates results in nucleophilic substitution of hydrogen and/or of the halogen. The reaction with halofumarates proceeds via addition of the carbanions to the vinylic carbon atom connected with hydrogen, followed by base promoted β-elimination of hydrogen halide in which the halogen originates from the carbanion moiety or from the alkene. In the case of halomaleates the reaction proceeds via an elimination-addition sequence.     

Control of the regioselectivity of sulfonamidyl radical cyclization by vinylic halogen substitution

The radical cyclization reactions of unsaturated sulfonamides were investigated. The photolysis of N-(4-halo-4-pentenyl)sulfonamides (X=I, Br, or Cl) with (diacetoxyiodo)benzene (DIB) and iodine at room temperature afforded exclusively the corresponding piperidines in 73-98% yield via 6-endo radical cyclization. On the other hand, the reactions of N-(5-halo-4-pentenyl)sulfonamides with DIB/I2 led to the only formation of the pyrrolidine products in 84-99% yield via 5-exo radical cyclization. The vinylic halogen substitution not only successfully inhibits the competing ionic iodocyclization process to allow the radical cyclization to proceed smoothly but also shows a remarkable effect in controlling the regioselectivity of cyclization.     

Pushing radical cyclization from regioselective to regiospecific: cyclization of amidyl radicals controlled by vinylic halogen substitution

Efficient and regiospecific 6-exo, 7-endo, 7-exo, and even 8-endo amidyl radical cyclizations can be accomplished by the direct reactions of unsaturated N-H amides if they bear a vinylic halogen (Cl, Br, I) substituent. This remarkable halogen-substitution effect could be rationalized in terms of lone pair-lone pair electron repulsion between the N radical and the vinylic halogen atom, in addition to the well-known steric and radical-stabilizing effect. [reaction: see text]     

Inversion versus retention of configuration for nucleophilic substitution at vinylic carbon

A high-level computational study using CCSD, CCSD(T), and G2(+) levels of theory has shown that unactivated vinyl substrates such as vinyl chloride would afford gas phase, single-step halide exchange by a pure in-plane sigma-approach of the nucleophile to the backside of the C--Cl sigma bond. Geometry optimization by CCSD/6-31+G* and CCSD(T)/6-31+G* confirms the earlier findings of Glukhovtsev, Pross, and Radom that the S(N)2 reaction of Cl(-) with unactivated vinyl chloride in the gas phase occurs by a sigma attack. Complexation of vinyl chloride with Na(+) does not alter this in-plane sigma preference. However, moderately activated dihaloethylenes such as 1-chloro-1-fluoroethylene undergo gas-phase S(N)2 attack by the accepted pi-route where the nucleophile approaches perpendicular to the plane of the C==C. In the latter case a single-step pi pathway is preferred for the Cl(-) + H(2)C==CFCl reaction. This is the first definitive example at a high level of theory where a single-step pi nucleophilic vinylic substitution is preferred over a multistep mechanism in the gas phase. The activation barriers for these gas-phase single-step sigma- and pi-processes involving both naked anions and Na(+) complexes are, however, prohibitively high. Solvation and the presence of a counterion must play a dominant role in nucleophilic vinylic substitution reactions that proceed so readily in the condensed phase. In solution, nucleophilic vinylic substitution reactions involving electron-withdrawing groups on the carbon--carbon double bond (e.g., -CN, -CHO, and -NO(2)) would almost certainly proceed via a free discrete carbanionic intermediate in accord with experiment.     

Facile 5-endo electrophilic cyclization of unsaturated amides with BuOCl/I2

5-Endo iodocyclization of various β,γ-unsaturated amides proceeded smoothly to give the corresponding conjugated iminolactones exclusively in satisfactory yields with the use of ^tBuOCl and I₂ as the reagents, which proved to be much advantageous over the conventional I₂/NaHCO₃.     

Stereoselective synthesis of vinylic chalcogenides through vinylic substitution by lithium organylchalcogenolates

Enol phosphates and enol tosilates of β-dicarbonyl compounds react with lithium organoselenolates to give β-organoseleno (Z)-α,β-unsaturated carbonyl compounds. Tetrasubstituted vinylic vic-bis(organylchalcogenides) of (E)-geometry have been prepared by this method.     

Halogenation reactions in position 3 of quinoline-2,4-dione systems by electrophilic substitution and halogen exchange

Summary 3-Substituted 4-hydroxy-2(1H)-quinolones3,5,7 are halogenated with bromine or sulfuryl chloride to yield the quinolinediones9 or10. Reaction of3,5,7 with chloroform gives the dichloromethyl quinolinediones11. Halogen exchange leads from the chloro quinolinediones10 to fluoro quinolinedones12 and to azido quinolinediones13. Similarly the dichloro quinolinedione10 an reacts to the difluoro quinolinedione14, which is reduced to the 3-fluoro-4-hydroxyquinolone16 and reacts again with sulfuryl chloride to give the mixed 3-chloro-3-fluoroquinolinedione15.Herrn Prof. Dr. Erich Ziegler in freundschaftlicher Verbundenheit zum 80. Geburtstag gewidmet.     

Nonaromatic corroles: regioselectivity of electrophilic substitution

Ring contraction of nickel meso-tetraarylporphyrins produced nonaromatic divalent corroles bearing a benzoyloxy function. We investigated their reactivity under electrophilic conditions: formylation, halogenation, nitration. We also found that the benzoate function could be eliminated to afford deoxocorroles, and we tested the formylation and nitration in this deoxo series. These corroles were generally very stable under the reaction conditions, and in both series, the directly bonded pyrroles were the most reactive. The nitration reaction produced a series of corrole dimers via electron transfer initiated coupling.     

p-Tolylsulfinyl amides: reagents for facile electrophilic functionalization of olefins

A variety of olefins were found to react with sulfinyl amides in the presence of POCl(3) to give beta-chlorosulfides and beta-hydroxysulfides in good yields. In the absence of nucleophiles, p-tolylsulfinyl amides were found to react with olefins with the formation of allylsulfoxides.     

Polymerization of N-methylpyrrole with bis-triazolinediones via electrophilic aromatic substitution

The reaction of N-methylpyrrole with 4-substituted-1,2,4-triazoline-3,5-diones (4R-TDs), i.e., MeTD (4-methylsubstituted) and PhTD (4-phenyl substituted), at room temperature without use of any catalyst was investigated. The reaction is instantaneous and leads to the formation of a 2:1 adduct in high yield, with substitution occurring at the 2 and 5 positions of the pyrrole moiety via electrophilic aromatic substitution. These compounds were fully characterized by IR,¹³C-NMR,¹H-NMR, and elemental analysis, and were used as model compounds for the polymerization reaction. The reaction of bis-triazolinediones with N-methylpyrrole was carried out in dimethylformamide at room temperature. The reactions are fast and give novel polymer structures. Some structural characterization and physical properties of these new polymers are reported.     

Reactions of highly electrophilic polyfluoro unsaturated compounds with pyrazole derivatives

Pyrazole derivatives were hydroxyalkylated at the C⁴ atom by hexafluoroacetate and methyl trifluoropyruvate. The products of the hydroxyalkylation were dehydrated to the corresponding alkylidene derivatives which were reacted with nucleophiles. Dicyanoethylenes, obtained from polyfluorocarbonyl compounds, alkylated pyrazol-5-ones with the formation of pyrazolopyran derivatives.A. N. Nesmeyanov Institute for Organometallic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2617–2623, November, 1992.     

Multiple electrophilic substitution of 1,1,2,2,9,9,10,10-octafluoro

Synthetic methods for introduction of two substituents into the rings of octafluoroparacyclophane are presented. Nitration gives three isomers with nitro substituents on different rings: pseudo-ortho, pseudo-meta, and pseudo-para, in equal amounts. These dinitro compounds are shown to be precursors of a variety of other disubstituted OFP derivatives. Methods of characterization of isomeric disubstituted OFPs are extensively discussed, and the 1H and 19F NMR spectra of these derivatives are analyzed explicitly.     

Nucleophilic vinylic substitution of halocoumarins and halo-l,4-naphthoquinones with morpholine

Reactions of morpholine with 4-halocoumarins 1 , 3-halocoumarins 3 , and 2-halo-l,4-naphthoquinones 8 yield two different products, one where halogen is replaced by a nucleophile at the same carbon and the other where the nucleophile is attached to the vicinal carbon away from that bearing the halogen. It is considered that reactions proceeds through nucleophilic vinylic substitution by comparision of the reaction products and deuterium exchange experiments. Plausible mechanisms for these routes are suggested.     

Benzamide synthesis by direct electrophilic aromatic substitution with cyanoguanidine

Cyanoguanidine is an inexpensive commodity chemical and it is found to be a useful reagent for the direct Friedel-Crafts carboxamidation of arenes. The reaction works best in an excess of Brønsted superacid, an observation suggesting the involvement of a superelectrophilic intermediate. Theoretical calculations indicate that the most stable diprotonated species involves protonation at the guanidine and cyano nitrogen atoms.     

Modification of polymers via electrophilic aromatic substitution

Three vinyl monomers, 2,4,6-trimethoxystyrene, 4-(N,N-dimethylamino)styrene, and N-methyl-2-vinylpyrrole, were synthesized via the Wittig reaction from the corresponding aldehyes. These monomers were homopolymerized by radical polymerization using α,α′-azoisobutyronitrile (AIBN) as initiator at 60°C. The reaction of these polymers with 4-phenyl-1,2,4-triazoline-3,5-dione (phTD) and 4-methyl-1,2,4-triazoline-3,5-dione (MeTD) was investigated. Although polytrimethoxystyrene reacts slowly with PhTD at room temperature, the other two polymers react fast and lead to the incorporation of the triazolinedione unit into the side chain of the polymer via electrophilic aromatic substitution. The reaction of bistriazolinediones (BTD) with these polymers was performed in dimethylformamide using 10–20% molar concentration of the BTD. The resulting crosslinked polymers are insoluble in polar as well as nonpolar solvents. Some physical properties of the unmodified and modified polymers were studied.     

A theoretical study of electrophilic aromatic substitution

To study the electrophilic reactant in the nitration reaction,ab initio molecular orbital calculations of the nitronium ion and its protonated derivative, as well as of the corresponding isoelectronic CO₂ and CO₂H⁺ systems, have been performed, with special reference to the stiffness of NO ₂ ⁺ and CO₂ to a bending of the \(\widehat{OXO}\) angle. According to these calculations, the nitronium ion and carbon dioxide have comparable bending constants.     

The effects of vinylic and allylic fluorine substitution in iso-butylene

Molecular orbital calculations using the 3-21G basis set have been performed for iso-butylene (IB; 2-methyl-1-propene), difluoro-iso-butylene (DFIB; 1,1-difluoro-2-methyl-1-propene), hexafluoro-iso-butylene (HFIB; 3,3,3-trifluoro-2-(trifluoromethyl)-1-propene), and perfluoro-iso-butylene (PFIB; 1,1,3,3,3-pentafluoro-2-(trifluoromethyl)-1-propene). The effects of fluorine substitution were studied by comparison of several calculated quantities of the fluorinated compounds with those of IB. Through an analysis of the computed electron density distributions, it is suggested that a vinylic fluorine acts as a π acceptor, by electron transfer into the C? F bond, and a π repeller, by polarization of the adjacent π electrons. An allylic fluorine acts as a π attractor through electrostatic effects, although in HFIB a minor contribution from hyperconjugation was evident. Finally, electrostatic potentials for the molecules were calculated. These show that fluorine substitution has large effects on the electrostatic potential associated with the π electrons. These effects change the sign of the calculated electrostatic potential in the plane containing the π bond to such an extent that PFIB is quite susceptible to nucleophilic attack.