Solvolysis of triaryliodoethylenes. Structure and selectivity of vinyl cations

Abstract

Reduction of a«» heptan-3-one (8). Lithium aluminum hydride reduction of pure 8 gave a mixture of 16 and 17 in 89 % yield.Reduction of iyn-7-Methoxytricyclo[2.2.1.02'6]heptan-3-one (18). Lithium aluminum hydride reduction of pure 18 gave pure 15. Identification was made by a comparison of infrared spectra and vpc retention times. Reaction of 7,7-Dimethoxybicyclo[2.2.1]hepta-2,5-diene (6) with Methanoiic Sulfuric Acid. The ketal 6 (194 mg) was treated with 10% methanoiic sulfuric acid for 21 hr at room temperature. Hydrolytic work-up as described for reactions of 4 gave benzene and no residue after removal of ether and benzene by distillation at reduced pressure.Equilibration of 3,3-Dimethoxytetracycio[2.2.0.02'7.04'6]heptane (4) with Ethanol via Acid Catalysis. A sample of 177 mg of 4 was dissolved in 249 mg of dry ethanol (distilled from magnesium ethoxide). The nmr spectrum was recorded and showed the spectrum of 4 superimposed on the spectrum of ethanol. The triplet observed for ethanol's hydroxyl proton demonstrated that the sample was acid free.A solution was prepared from 19 mg of sulfuric acid and 3.34 g of dry ethanol, and 86 mg of this solution was added to the nmr tube containing 4 and ethanol. The tube was shaken vigorously and the nmr spectrum was recorded (total elapsed time 100 sec).In addition to showing the simplified ethanol spectrum (due to acid-catalyzed exchange of the hydroxyl proton), the spectrum showed a drastic decrease in the relative intensity of the absorption due to the dimethyl ketal and the presence of a new absorption due to methanol. This spectrum of equilibrated material did not undergo further change on rerunning.

Molecular orbital theory of the electronic structure of molecules. 36. A theoretical study of several .alpha.-substituted vinyl cations

“…In the extreme case (cation 2), 1.2 of the vinylic double-bond electrons are located at the a carbon and only 0.8 at the ß carbon, pointing to a contribution from the resonance form H2C+-CH. 42 The polarization is smaller for the other cations, although significant (0.1 electron) even in the phenylvinyl cation (7a). Thus, although the cationic 2p (C+) orbital and the CjC2 electrons occupy two perpendicular planes and cannot interact directly, they are strongly coupled through polarization effects.…”

Vinylic cations from solvolysis. XX. Ion pairs and free ions in the solvolysis and isomerization of 1,2-dianisyl-2-phenylvinyl halides and mesylates. Use of cis-trans isomerization as a mechanistic tool

“…In [100/(100 -x)]/t + In [1/(1 -y/46)}/1 (15) kt + klaom = In [100/(100 -x)]/t + In [46/(46 -y)}/t = In [100/(100 -x)}/t + In [ 1/(1 -y/46)]/1…”

“…Scheme VII is disproved by the following reasoning, (a) The best "special" salt, LÍCIO4,5 did not show special salt effect. If 14 is captured completely by NaOAc, exchange of 15 with LÍCIO4 would give Li+||C104-ion pairs and lower extent of ICRD than with NaOAc alone. However, Table III shows a similar common ion rate depression with and without LÍCIO4.…”

“…These include the loss of optical activity (ka or &rac),3•6 the concurrent rearrangement in either R3-7a or X,3 7b and the oxygen equilibration in a leaving group which carries several oxygen atoms.3-8 Dissociated (free) carbonium ions are recognized by the appearance of common ion rate depression by the common ion Xor by exchange of X in RX by labeled X">c Information regarding the nature of cationic intermediates in vinylic solvolysis9 is scarce. Product formation from dissociated ions is evident from common ion rate depression in the solvolysis of several -arylvinyl systems where X = Cl,10,11 Br,9,10c, 12-14 , 15 2,4,6-(02N)3C6H20S02,16 and OTsi4b.i7 jn soivents such as AcOH,2•103•0•12 AcOH-HCOOH mixtures,20 aqueous EtOH,10bn acetone,166 aqueous acetone,11•17 aqueous DMF,15 and 2,2,2-trifluoroethanol (TFE).14 Ion pairs were invoked to explain the predominant inversion in the solvolysis of several vinyl Inflates,18•19 the faster elimination from trans-1,2-dimethylvinyl trifíate with NaOH than in neutral solution,180 the smaller substituent effects in the solvolysis of acyclic vinyl triflates compared with 1-cyclohexenyl triflate,180 the small amount of cistrans interconversion of 1 -cyclopropyl-1 -iodopropenes with AgOAc in AcOH20 and of cis--bromoanethole in 80%…”

Synthesis of substituted hydroazulenes

“…In addition, conformational analysis is useful in predicting the relative stability of isomers in such systems.1 Unfortunately, a similar body of information is not available for the stereoselective construction of substituted hydroazulenes, and the application of conformational analysis to substituted seven-membered rings is relatively difficult.2 Recently, a large and relatively important group of sesquiterpenes, the pseudoguaianolides, has been shown to possess the hydroazulene ring system.3 Damsin (1) is a typical representative of this family of 1 compounds. 4 As a result of our interest in these sesquiterpenes, this work was initiated to develop stereoselective methods for the preparation of substituted and functionalized hydroazulenes, with particular reference to the substitution patterns typical of the pseudoguaianolides.…”