V. A. Bushmelev

Degenerate rearrangement of detectable 9,10-dimethyl-9-vinyl-phenanthrenium ion : 1,2-shift of the vinyl group

Dynamic NMR study showed that 9,10-dimethyl-9-vinylphenanthrenium ion, generated under the conditions ensuring its “long life,” undergoes very fast (ΔG≠ = 24.4 kJ/mol at −103°C) degenerate 1,2-shift of the vinyl group. According to the DFT quantum-chemical calculations, the process is one-step, and the low energy of formation of the activated complex is determined by effective participation of π electrons of the vinyl group in delocalization of the positive charge; no such delocalization is intrinsic to the initial ion.

Carbocationic Cyclizations: IX. Rearrangement of Long-Lived 4-(2-Biphenylyl)-1,2,3,4-tetramethylcyclobutenyl Cation into trans- and cis-4,5,6,6-Tetramethyl-4,5,6-trihydrocyclopenta[j,k]phenanthren-5-yl Cations

According to the 1H and 13C NMR data, long-lived 4-(2-biphenylyl)-1,2,3,4-tetramethylcyclobutenyl cation generated by protonation of 3-(2-biphenylyl)-1,2,3-trimethyl-4-methylenecyclobutene in super-acids undergoes cyclization which launches further rearrangements finally leading to formation of a mixture of trans- and cis-4,5,6,6-tetramethyl-4,5,6-trihydrocyclopenta[j,k]phenanthren-5-yl cations.

Reaction of 10,10-dimethyl-9-trimethylsiloxy-9,10-dihydrophenanthrene-9-carbonitrile with acids

The behavior of 10,10-dimethyl-9-trimethylsiloxy-9,10-dihydrophenanthrene-9-carbonitrile in trifluoromethanesulfonic acid and acid systems CF3SO3H-CD2Cl2, HSO3F-SO2ClF-CD2Cl3, and CF3COOH-CD2Cl2 were studied by NMR spectroscopy. Principal reaction schemes were determined; the first step in these schemes is protonation of the initial compound at the oxygen or nitrogen atom.

Long-Lived 9-Cyano-9,10-dimethylphenanthrenyl Cation. Migration of Cyano Group in Carbocations

Long-lived 9-cyano-9,10-dimethylphenanthrenyl cation was generated in superacidic medium, and its structure was determined by 1H and 13C NMR spectroscopy. The energy barrier to 1,2-shift of the cyano group in 9-cyano-9,10-dimethylphenanthrenyl cation was estimated by NMR and DFT calculations.

Degenerate rearrangement of 9-isopropenyl-9,10-dimethyl-phenanthren-9-yl and 9,10-dimethyl-9-(trans-1-methylprop-1-en-1-yl)phenanthren-9-yl cations

Abstract1H NMR study has shown that long-lived 9-R-9,10-dimethylphenanthren-9-yl cations (R = isopropenyl, trans-1-methylprop-1-en-1-yl) generated in the system HSO3F-SO2ClF-CD2Cl2 at −130°C undergo degenerate rearrangement via 1,2-vinyl shifts (ΔG’ = 37 and 39 kJ/mol, respectively, at −88°C). Analysis of the geometric parameters of the initial structures and transition states calculated by the DFT method indicates that unfavorable steric factors are responsible for the sharp deceleration of 1,2-shifts of the isopropenyl and trans-1-methylprop-1-en-1-yl groups as compared to vinyl and cis-1-methylprop-1-en-1-yl groups, respectively.

Structure of long-lived alkynyl-substituted carbocations of the phenanthrene series and their precursors

According to the NMR data, 9-(R-ethynyl)-9-hydroxy-10,10-dimethyl-9,10-dihydrophenanthrenes (R = H, Me, Ph) in superacid medium (HSO3F-SO2ClF) at low temperature undergo dehydroxylation with formation of the corresponding long-lived 10,10-dimethyl-9-(R-ethynyl)-9,10-dihydrophenanthren-9-yl cations which do not isomerize to 10-(R-ethynyl)-9,10-dimethyl-9,10-dihydrophenanthren-9-ylium. In contrast, longlived 10,10-dimethyl-9-(3,3,3-trifluoroprop-1-yn-1-yl)-9,10-dihydrophenanthren-9-yl cation derived from 9-(3,3,3-trifluoroprop-1-yn-1-yl)-10,10-dimethyl-9,10-dihydrophenanthren-9-ol undergoes partial isomerization to 10-(3,3,3-trifluoroprop-1-yn-1-yl)-9,10-dimethyl-9,10-dihydrophenanthren-9-yl cation.

Structural nonrigidity of 9,9,10-trimethyland 4,5,9,9,10-pentamethylphenanthrenylium ions

DFT quantum-chemical calculations predicted structural nonrigidity of 9,9,10-trimethyl- and 4,5,9,9,10-pentamethylphenanthrenylium ions. The cross section of the potential energy surface at the nonrigidity coordinate for the first of these ions is symmetric, and for the second, asymmetric. These results were confirmed experimentally: the 13C NMR spectra of 4,5,9,9,10-pentamethylphenanthrenylium showed considerable temperature dependence of chemical shifts which is not typical of 9,9,10-trimethylphenanthrenylium.

Cyclization reactions of long-lived 10,10-dimethyl-9-phenylethynyl-9,10-dihydrophenanthren-9-yl cation

According to the NMR data, long-lived 10,10-dimethyl-9-phenylethynyl-9,10-dihydrophenanthren-9-ylium in acid medium undergoes cyclization whose direction is determined by the acidity of the medium. The cyclization in HSO3F-SbF5 superacid involves the aromatic ring in the phenanthrene core as nucleophilic component and yields 5a,6-dimethyl-4-phenyl-4,5,5a,6-tetrahydroacephenantrylene-4,6-bis(ylium). In trifluoroacetic acid the nucleophilic component is the side-chain phenyl group, and the cyclization product is neutral 8b,14b-dimethyl-8b,14b-dihydrobenzo[g]chrysen-10-yl trifluoroacetate. Both cyclization directions are observed in moderate-strength trifluoromethanesulfonic acid.

Rearrangements of 1-(1-methylprop-1-en-1-yl)-1,2-dimethylacenaphtyylenonium ions

It was discovered by means of dynamic NMR that the 1-(cis-1-methylprop-1-en-1-yl)-1,2-dimethylacenaphthylenonium ion generated under conditions of “long life” for carbocations underwent fast (ΔG#35.8 kJ mol−1 at −103°C) degenerate 1,2-shift of the cis-dimethylvinyl group. Quantum-chemical calculations by DFT method predict lower rate of 1,2-shift for the trans-dimethylvinyl group compared to cis-dimethylvinyl group and dependence on the cations conformation of the rates of these processes and of the rearrangement mechanism into the ions of phenalenyl type.

Formation of dications bearing a S(OH)2+ group from long-lived 9,9-dimethyl-10 R-phenanthrenium cations in FSO3H–SbF5/SO2ClF/SO2: a mechanistic study

1 H and 13C NMR studies have shown that the long-lived 9,9-dimethyl-10-R-phenanthrenium cations (R = PhCC, Me, OH) generated in FSO3H–SbF5/SO2ClF/SO2/CD2Cl2 transform into long-lived 7-dihydroxysulfonio-9,9-dimethyl-10-R-phenanthrenium dications. The effect of the 10-R substituents on the reaction rate suggests that a key step in the reaction mechanism is addition of SO2 to protonated phenanthrenium cations.