Aminosulfenates in the electrophilic addition reactions

The reactions of methyl and ethyl diethylaminosulfenates and ethyl piperidinylsulfenate with cyclohexene and norbornene in the presence of chloro- or bromotrimethysilanes were studied.     

Gas-phase electrophilic addition promoted by CH(3)S(+)=CH(2) ions on aromatic systems

The gas-phase methylenation reaction between CH(3)S(+)=CH(2) and alkylbenzenes, aniline, phenol and alkyl phenyl ethers, which yields [M + CH](+) and CH(3)SH, has been studied by Fourier transform ion cyclotron resonance (FT-ICR) techniques and computational chemistry at the DFT level. The methylthiomethyl cation is less reactive than methoxymethyl and, unlike the latter, is unreactive toward benzene. The calculations suggest that reaction with toluene should proceed primarily by addition at the para and ortho positions resulting in a benzyl-type ion. Reaction with aniline-2,3,4,5,6-d(5) reveals that elimination of CH(3)SD is kinetically favored by a factor of 5 over elimination of CH(3)SH. Experiments with C(6)H(6)ND(2) and theoretical calculations suggest that methylenation at the nitrogen atom is energetically favorable and likely, but the observed results may reflect some H/D scrambling, which occurs after attack at a ring position. By comparison, reaction with phenol-2,3,4,5,6-d(5) reveals that methylenation followed by elimination of CH(3)SD is kinetically favored by a factor of 3.8 over elimination of CH(3)SH. For phenol, the theoretical calculations suggest that attack by CH(3)S(+)=CH(2) at the para or ortho position is the only low-energy pathway for methylenation. However, a low-energy pathway for hydrogen scrambling is predicted by the calculations originating from the exit complex, [CH(3)SH(...) CH(2)=C(6)H(4)=OH](+), of reaction at a ring position.     

Gas-phase reactions of organic radicals and diradicals with ions

Reactions of polyatomic organic radicals with gas phase ions have been studied at thermal energy using a flowing afterglow-selected ion flow tube (FA-SIFT) instrument. A supersonic pyrolysis nozzle produces allyl radical (CH2CHCH2) and ortho-benzyne diradical (o-C6H4) for reaction with ions. We have observed: [CH2CHCH2 + H3O+ --> C3H6+ + H2O], [CH2CHCH2 + HO- --> no ion products], [o-C6H4 + H3O+ --> C6H5+ + H2O], and [o-C6H4 + HO- --> C6H3- + H2O]. The proton transfer reactions with H3O+ occur at nearly every collision (kII approximately with 10(-9) cm3 s(-1)). The exothermic proton abstraction for o-C6H4 + HO- is unexpectedly slow (kII approximately with 10(-10) cm3 s(-1)). This has been rationalized by competing associative detachment: o-C6H4 + HO- --> C6H5O + e-. The allyl + HO- reaction proceeds presumably via similar detachment pathways.     

N-alkoxy-n-acylnitrenium ions in intramolecular aromatic addition reactions

N-alkoxy-N-acylnitronium ions are generated by treatment of N-alkoxy-N-cohloroamides with silver ions in ethereal solvents. These intermediates readily cyclise onto aromatic nuclei on alkozy side-chains to give benzoxazines and benzoxazepines and on the acyl side-chains to give γ, δ and ϵ benzolactams. Spirane products are formed by ipso addition When a 4-methoxy substituent ia present on the side-chain aromatic rings. The yields and regioselectivities of these reactions have been ascribed to different transition structures for cyclisation onto the acyl and alkoxy side-chains which involve respectively an exocyolic and endocyclic N-0 π-bond. Evidence for this exeptionally high π-bond character has been obtained from MNDO calculations which predict a π-bond order of 0.9 and a rotational barrier of 29.7 kcalmol^-1     

Gas-phase ion/molecule reactions between dimethoxyphosphonium ions and aromatic hydrocarbons

Ion/molecule reactions between O=P(OCH(3))(2)(+) phosphonium ions and six aromatic hydrocarbons (benzene, toluene, 1,2,4-trimethylbenzene, naphthalene, acenaphthylene and fluorene) were performed in a quadrupole ion trap mass spectrometer. The O=P(OCH(3))(2)(+) phosphonium ions, formed by electron impact from neutral trimethyl phosphite, were found to react with aromatic hydrocarbons (ArHs) to give (i) an adduct [ArH, O=P(OCH(3))(2)](+) and (ii) for ArHs which have an ionization energy below or equal to 8.14 eV, a radical cation ArH(+ *) by charge transfer reaction. Collision-induced dissociation experiments, which produce fragment ions other than the O=P(OCH(3))(2)(+) ions, indicate that the adduct ions are covalent species. Isotope-labeled ArHs were used to elucidate fragmentation mechanisms. The charge transfer reactions were investigated using density functional theory at the B3LYP/6-311 + G(3df,2p)//B3LYP/6-31G(d,p) level of theory. The potential energy surface obtained from B3LYP/6-31G(d,p) calculations for the reaction between O=P(OCH(3))(2)(+) and benzene is described.     

Gas-phase uranyl-nitrile complex ions

Electrospray ionization was used to generate doubly charged complex ions composed of the uranyl ion and nitrile ligands. The complexes, with general formula [UO2(RCN)n]2+, n = 0-5 (where R=CH3-, CH3CH2-, or C6H5-), were isolated in an ion-trap mass spectrometer to probe intrinsic reactions with H2O. For these complexes, two general reaction pathways were observed: (a) the direct addition of one or more H2O ligands to the doubly charged complexes and (b) charge-reduction reactions. For the latter, the reactions produced uranyl hydroxide, [UO2OH], complexes via collisions with gas-phase H2O molecules and the elimination of protonated nitrile ligands.     

A new method for the activation of ethyl benzenesulfenate in electrophilic addition reactions

Reactions of unsaturated compounds with the PhSOEt-SOHal₂ and PhSOEt-Me₃SiHal systems (Hal = Cl or Br) were proposed as a new route to haloalkyl phenyl sulfides. With acyclic and mono- and bicyclic alkenes and dienes as examples, the regio- and stereoselectivity of the reactions were studied.     

Gas-phase transuranium chemistry: reactions of actinide ions with alcohols and thiols.

The laser ablation with prompt reaction and detection method was employed to provide a survey of some gas-phase reactions of actinide (M = U, Np, Pu and Am) and lanthanide (M = Tb and Tm) ions, M(+) and MO(1,2)(+), with alcohols, thiols and ethers. Particular attention was given the changing behavior in progressing across the actinide series beyond uranium. With alcohols, ROH, major products included hydroxides and alkoxides, M(OH)(1,2)(+), M(OR)(1,2)(+), MO(OH)(+) and MO(OR)(+); these products are presumed to have resulted from RO&bond;H and R&bond;OH bond cleavage by ablated M(+) and MO(+). The abundance distributions for these elementary products reflected the decrease in stabilities of high oxidation states between U and Am. Other alcohol reaction products included electrostatically bonded adducts, such as HO&bond;Np(+)ellipsisC(3)H(7)OH, sigma-bonded organometallics, such as HO&bond;Pu(+)&bond;C(2)H(5), and pi-bonded organometallics, such as Np(+)&bond;eta(3)-?C(3)H(5)?. In view of the inability of actinide and lanthanide ions to dehydrogenate alkanes, the exhibition of dehydrogenation of the alkyl chain of alcohols, as in HO-Pu(+)-C(3)H(5)O from propanol, suggests a non-insertion mechanism involving complexation of the reactant ion to the alcohol. Whereas O abstraction products from ROH were obfuscated by directly ablated MO(1,2)(+), S abstraction from thiols, RSH, was manifested by the appearance of MS(+), MS(2)(+) and MOS(+). In analogy with OH abstraction from alcohols to produce metal hydroxides, SH abstraction from thiols resulted in hydrosulfides, including Am(SH)(+) and Np(SH)(2)(+). In addition to several other reaction pathways with the thiol reagents, products presumed to be thiolates included Am(C(3)H(7)S)(+) and NpO(C(3)H(7)S) from propanethiol. A primary product of reaction with dimethyl ether were methoxides resulting from C--O bond cleavage, including Am(OCH(3))(+) and Np(OCH(3))(2)(+). With methyl vinyl ether, more complex pathways were exhibited, most of which corresponded to the elimination of stable organic molecules. An ancillary result was the discovery of several small oxide clusters, Am(2)O(n)(+), Np(2)O(n)(+) and AmNpO(n)(+). The compositions and abundance distributions of these clusters reflected the propensity of Np to exist in higher oxidation states than Am; the dominant binary clusters were Am(2)O(2)(+) and Np(2)O(3)(+).     

Gas-phase electrophilic attack of a double bond exhibits stereoselectivity

Protonated acetaldehyde (ion 1) reacts with allyltrimethylsilane (allyl-TMS) in the gas phase to yield cis-piperylene (cis-1,3-pentadiene) as the major product. The cis isomer predominates over trans by a factor >/=15:1, a degree of stereoselectivity that is unprecedented in a reaction where the double bond geometry has not been specified in the reactant. The neutral products were assessed by creating tritiated 1 via decay of a tritium nucleus in gaseous ethanol molecules labeled with >1 tritium atom. The radioactive C5H8 products must result from addition of the electrophilic ion to the allyl group followed by an elimination. Deprotonation of C5H9+ cannot account for the product stereochemistry. One possible explanation is that addition of the electrophile to the double bond is followed by elimination of Me3SiOH2+ on a time scale faster than that by which the initially formed adduct ion can change its conformation.     

Borate promoted electrophilic additions of alkyl hypohalites

Catalysis by trimethyl borate promotes a rapid ionic reaction of methyl hypobromite with alkenes and dienes in methylene chloride.     

Monoterpenoids (3-carene and α-terpinene) in electrophilic disulfide addition reactions

The reactions of 3-carene and α-terpinene with dialkyl disulfides have been studied. S. V. Kurashov Kazan' State Medical Institute. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 624–626, September–October, 1990.     

Gas-phase radiation-chemical formation of dioxins from chlorinated phenols

The gas-phase radiation-chemical formation of dioxins from chlorinated phenols in the electron-beam removal of toxic impurities from industrial gases is considered. A kinetic model of the process is proposed. Conditions under which the efficiency of removal of the above compounds from gases significantly decreases were determined with the use of this model. The results of a numerical simulation are compared with currently available experimental data.     

Stereoselectivity in the electrophilic addition reactions of stigmast-22(23)-ene derivatives

Oxidation of 5α-stigmast-22-en-3- one (1) with m-chloroperbenzoic acid afforded [22R,23R]-epoxide 3 and [22S, 23S]-epoxide 2, in a 5:3 ratio. Reaction of 1 with iodine/silver acetate gave a mixture of iodoacetates 8 and 9, which on treatment with base yielded the single epoxide 2. Those results suggest that electrophiles may preferentially approach the Δ²²-bond from the side of the 21-Me group, in accordance with observations with the ergosterol-like side chain.     

Gas-phase reactions of protonated tryptophan

The gas phase reactions of protonated tryptophan have been examined in a quadrupole ion trap using a combination of collision induced dissociation, hydrogen-deuterium exchange, regiospecific deuterium labeling and molecular orbital calculations (at the B3LYP/6-31G* level of theory). The loss of ammonia from protonated tryptophan is observed as the primary fragmentation pathway, with concomitant formation of a [M + H - NH(3)](+) ion by nucleophilic attack from the C3 position of the indole side chain. Hydrogen-deuterium exchange and regiospecific deuterium labeling reveals that scrambling of protons in the C2 and C4 positions of the indole ring, via intramolecular proton transfer from the thermodynamically preferred site of protonation at the amino nitrogen, precedes ammonia loss. Molecular orbital calculations have been employed to demonstrate that the activation barriers to intramolecular proton transfer are lower than that for NH(3) loss.     

Quantum chemical studies on electrophilic addition

The geometries of the 2-hydroxyethyl and isomeric oxiranium cations have been fully optimized using ab initio molecular orbital calculations employing the split valence shell 4-31G basis set. These species are possible intermediates in both the electrophilic addition of OH to ethylene and in the acid catalysed ring opening of oxirane. The optimized structures were then used to compute more accurate wave functions using Dunning's double-zeta basis set, and with this large basis set the bridged oxiranium ion was found to be the more stable by 7.2 kcal/mole. The barrier to interconversion of these two C₂H₄OH ions was computed to be 25.0 kcal/mole above the oxiranium ion.     

Gas-phase reactions of nitronium ions with acetylene and ethylene: an experimental and theoretical study

A comparative study of the gas-phase reactions of NO2+ with acetylene and ethylene was performed by using FT-ICR, MIKE, CAD, and NfR/ CA mass spectrometric techniques, in conjunction with ab initio calculations at the MP2/6-31+G* level of theory. Both reactions proceed according to the same mechanism, that is, 1,3-dipolar cycloaddition, but yield products of different stability. The C2H2NO2+ adduct from acetylene has an aromatic character and hence is highly stabilized with respect to the C2H4NO2+ adduct from ethylene. Both cycloadducts tend to isomerize into O-nitroso derivatives, that is, nitrosated ketene and nitrosated acetaldehyde, which represent the thermodynamically most stable products from the addition of NO2+ to acetylene and ethylene, respectively. As prototypal examples of the reactivity of free nitronium ions with most simple pi systems, the reactions investigated are useful starting points to model the mechanism of aromatic nitration.