2167-32-0Relevant academic research and scientific papers
1,2-Bis(trifluoromethyl)ethene-1,2-dicarbonitrile: (2+2) cycloadditions with vinyl ethers
Urrutia-Desmaison, Gonzalo,Huisgen, Rolf,Noeth, Heinrich
experimental part, p. 1 - 16 (2012/03/07)
The title compound (short version: BTE) occurs in (E)- and (Z)-isomers (both with b.p. of ca. 100°) which equilibrate with nucleophilic catalysts. Both undergo (2+2) cycloadditions with methyl vinyl ether at 25°. Three stereogenic centers in the cyclobutanes led to four rac-diastereoisomers, which were obtained in pure and crystalline state. The structures were elucidated by 19F-NMR spectroscopy and confirmed by two X-ray analyses. The cycloadditions were not stereospecific: e.g., (E)-BTE furnished 73% trans-adducts (with respect to the CF3 groups) and 27% cis-adducts. The loss of stereochemical integrity occurs in the intermediate gauche-zwitterions which can cyclize or rotate, but not dissociate. Under extreme conditions (2M LiClO4 in Et2O, 70°, 3months), the thermodynamic equilibrium of the four cyclobutanes was achieved. Considerations of Coulombic attraction and conformational strain in the zwitterionic intermediates allow us to rationalize the observed proportions of diastereoisomeric cyclobutanes. Ethyl vinyl ether and butyl vinyl ether furnished cyclobutanes in similar diastereoisomer ratios. Copyright
Reactions of sterically hindered 'thiocarbonyl ylides' with 1,2-bis(trifluoromethyl)ethene-1,2-dicarbonitrile: Isolation of a cyclic seven-membered ketene imine
Huisgen, Rolf,Mloston, Grzegorz,Langhals, Elke,Oshima, Takumi
, p. 2668 - 2685 (2007/10/03)
When 'thiocarbonyl ylide' 1A (=(2,2,4,4-tetramethyl-3-oxocyclobutylidenesulfonio)methanide) is generated from the dihydrothiadiazole 5A by N2 extrusion at 40° in the presence of 2,3-bis(trifluoromethyl)fumaronitrile ((E)-10), a cyclic seven-membered ketene imine 11 and trans-thiolane 12 are formed (81:19). The reaction of 1A with (Z)-10 furnishes 11, 12, and cis-thiolane 25 in the ratio of 82:12:6. The strained ketene imine 11 is crystalline and storable as a consequence of the stabilizing 'perfluoroalkyl effect'. The ketene imine group is stereogenic; 11 has a transoid structure with respect to the CF3 groups, and there is no evidence for the cisoid diastereoisomer. Ketene imine 11 adds H2O. MeOH, and PhNH2. In solution at 60°, 11 undergoes an irreversible ring contraction, furnishing the thiolanes 12/25 98:2. The rate constant of this first-order rearrangement increases 850-fold, as the solvent polarity rises from cyclohexane to CD3CN, in accordance with a zwitterionic intermediate. It is the same intermediate that is initially formed from 1A and 10, and its intramolecular N- and C-alkylation give rise to 11 and 12 + 25, respectively. In contrast to 1A, thiocarbonyl ylide 27, which harbors the sterically less-demanding adamantylidene group, reacts with (E)-10 to give trans-thiolane 29, but no ketene imine. The precursor 26 catalyzes the (Z)/(E) isomerization of 10 ((E)/(Z) ca. 95:5 at equilibrium), thus obviating conclusions on steric course and mechanism of this cycloaddition.
