[2 + 3]‐Cycloadditions of Phosphonodithioformate S‐Methanides with CS,NN,and CC Dipolarophiles

The reaction of the methyl (dialkoxyphosphinyl)‐dithioformates (= methyl dialkoxyphosphinecarbodithioate 1‐oxides) 10 with CH₂N₂ at − 65° in THF yielded cycloadducts which eliminated N₂ between − 40 and − 35° to give the corresponding phosphonodithioformate S‐methanides ( =methylenesulfonium (dialkoxyoxidophosphino)(methylthio)methylides) 11 (Scheme 3). These reactive 1,3‐dipoles were intercepted by aromatic thioketones to yield 1,3‐dithiolanes. Whereas the reaction with thiobenzophenone ( 12b ) led to the sterically more congested isomers 15 regioselectively, a mixture of both regioisomers was obtained with 9H‐fluorene‐9‐thione ( 12a ). Trapping of 11 with phosphono‐ and sulfonodithioformates led exclusively to the sterically less hindered 1,3‐dithiolanes 16 and 18 , respectively (Scheme 4). In addition, reactive CC dipolarophiles such as ethenetetracarbonitrile, maleic anhydride, and N‐phenylmaleimide as well as the NN dipolarophile dimethyl diazenedicarboxylate were shown to be efficient interceptors of 11 (Scheme 5).     

Structures and isomerizations of carbenoids H2CCCLiX (X  F,Cl)

Novel structures of H₂C?C?CLiX (X ? F, Cl) were determined using HF/STO-3G gradient method. Both of the carbenoids have two equilibrium structures, askew and linear forms, at the level of calculation. In the case X?F, the former is more stable, but in the case X=Cl, the latter is more stable. The frontier MOs are given and analyzed.     

Organocatalysis of CN/CN and CC/CN Exchange in Dynamic Covalent Chemistry

The reversibly formed C?N bond plays a very important role in dynamic covalent chemistry and the C?N/C?N exchange of components between different imine constituents to create dynamic covalent libraries has been extensively used. To facilitate diversity generation, we have investigated an organocatalyzed approach, using L ‐proline as catalyst, to accelerate the formation of dynamic libraries of [n×n] imine components. The organocatalysis methodology has also been extended, under somewhat modified conditions, to reversible C?C/C?N exchange processes between Knoevenagel derivatives of barbituric acid and imines, allowing for the generation of increased diversity.     

Random and sequential radical cotelomerizations of 3,3,3‐trifluoropropene (H2CCHCF3) with vinylidene fluoride (F2CCH2)

The synthesis of original cotelomers based on 3,3,3‐trifluoropropene (TFP) and vinylidene fluoride (VDF) with a general formula: R_F‐[CH₂? CF₂]_n? [CH₂? CH(CF₃)]_m? I (where n = 1–63, m = 2–640, and R_F = (CF₃)₂CF) was achieved by sequential and random cotelomerizations in the presence of R_FI. The radical cotelomerizations were initiated by thermal decomposition of different peroxide and persulfate initiators either in bulk, in solution (in the presence of acetonitrile or 1,1,1,3,3‐pentafluorobutane as the solvents), and in aqueous process (emulsion). Different adducts were obtained in good yield (50–70 wt %) with a relative proportion of each adduct depending on (i) the R₀ = [R_FI]₀/([TFP]₀+[VDF]₀) initial molar ratio, (ii) the reaction temperature, and (iii) C₀ = [In]₀/([TFP]₀+[VDF]₀). Random cotelomerization gave higher yields than those obtained from the sequential cotelomerization. When the concentration of the chain transfer agent increased, the molecular weights of the resulting poly(VDF‐co‐TFP) cotelomers decreased and showed that the R₀ ratio targeted the molecular weights (～700–66,000 g mol^?1). Some of the obtained molecular weights were exceptionally high for a (co)telomerization. The kinetics of the radical cotelomerization of VDF and TFP led to the determination of the reactivity ratios of both comonomers (r_VDF = 0.28 ± 0.07 and r_TFP = 2.35 ± 0.26 at 75 °C). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3964–3981, 2009     

Selenoketene (H2CCSe)+• and selenoketyl cumulene (HCCSe)+ ions and their neutral counterparts: a tandem mass spectrometric and computational study

Dissociative electron ionization (70eV) of selenophene (C₄H₄Se) generates m/z 106 ions of composition [H₂, C₂, ⁸⁰Se]^+? and m/z 105 ions of [H, C₂, ⁸⁰Se]⁺. From tandem mass spectrometric experiments, Density Functional Theory (DFT) and ab initio calculations, it is concluded that these ions have the structure of selenoketene H₂C?C?Se^+? (1a^+? )and selenoketyl HC?C?Se⁺ (2a⁺) ions respectively. The calculations predict that selenoketene ion 1a^+? is separated by high energy barriers from its isomers selenirene (H e)^+? 1b^+?, ethyne selenol (HCCSeH)^+? 1c^+?, (CCHSeH)^+? 1d^+? and (CCSeH₂)^+? 1e^+?. The selenoketyl ion 2a⁺ is separated by high barriers from its isomers (CCHSe)⁺ 2b⁺, and (CCSeH)⁺ 2c⁺. Neutralization‐reionization mass spectra (NRMS) of these structurally characterized ions confirmed that the corresponding neutral analogues, selenoketene H₂CCSe 1a and selenoketyl radical HCCSe 2a^? are stable in the rarefied gas phase. The relative, dissociation, and isomerization energies for selenoketene and selenoketyl ions and neutrals studied at B3LYP/6–31G(d,p) and G2/G2(MP2) levels are used to support and interpret the experimental results. Copyright © 2005 John Wiley & Sons, Ltd.     

Darstellung der Dichlormethyleniminium-Salze Cl2CNClH+ MF6− und Cl2CNClCH3+ MF6− (M = As,Sb) und Kristallstruktur von Dichlormethyleniminiumhexachloroantimonat Cl2CNH2+SbCl6−

Synthesis of the Dichloromethyleneiminium Salts Cl₂C?NClH⁺MF₆^? and Cl₂C?NClCH₃⁺ MF₆^? (M = As, Sb) and Crystal Structure of Dichloromethyleneiminium-hyxachloroantimonate Cl₂C?NH₂⁺SbCl₆^? The N-chloro-dichloromethyleneiminium salts Cl₂C=NCIH⁺MF₆^? (M = As, Sb) are prepared by protonationof trichloromethyleneimine in the superacide system HF/MF5 at 195 K. The synthesis of the N-chloro-N-methyl-dichloromethyleneiminium salts Cl₂C?NClCH₃⁺MF₆^? (M = As, Sb) is proceeded by methylation of perchloromethylenimine by CH₃OSO⁺MF₆^? in SO₂ also at low temperature. All salts are characterized by vibrational and NMR spectra. The dichloromethyleneiminiumhexachloroantimonate crystallizes in the space group P2₁/c with a = 971.3(4)pm, b = 1134.0(4)pm, c = 2154.2(7)pm β = 102.04(3)° and Z = 8.