Homoaromaticity in aza‐ and phosphasemibullvalenes. A computational study

Abstract

The enthalpies of activation ΔH‡ for the Cope rearrangement in several aza‐ and phosphasemibullvalenes have been investigated by MP4/cc‐pVDZ//MP2/cc‐pVDZ and CCSD(T)/cc‐pVDZ//MP2/cc‐pVDZ calculations. One tetraazasemibullvalene and several phosphasemibullvalenes were found to have vanishing ΔH‡ values, which together with calculated large negative Nucleus Independent Chemical Shift (NICS) values and geometrical data show that these molecules have delocalized and bishomoaromatic minima. Furthermore, three azasemibullvalenes were found to have small ΔH‡ values (≤2 kcal/mol) combined with large negative NICS, suggesting that they could also have bishomoaromatic minima. Copyright © 2010 John Wiley & Sons, Ltd.

Diastereoselective Nucleophilic Ring‐Opening Reactions of 2,6‐Diazasemibullvalenes for the Synthesis of Diverse Functionalized Δ1‐Bipyrroline Derivatives

“…After removal of the solvent under vacuum, purification by column chromatography (silica gel, petroleum ether/diethyl ether/triethylamine = 100:3:1) gave product 2. Compound 2 a: Yellow oil; 55 % (84 mg); 1 21.68, 28.00, 28.95, 30.13, 32.80, 35.32, 35.66, 43.24, 59.42, 79.82, 81.76, 92.54, 178.95, 181.16 20.87, 21.04, 27.89, 28.62, 29.69, 32.28, 35.04, 35.53, 43.35, 79.89, 81.05, 86.44, 114.88, 120.83, 129.46, 157.99, 178.54, 182.47 21.53, 22.40, 27.81, 28.20, 30.48, 32.81, 35.28, 35.61, 43.16, 79.68, 80.07, 81.92, 128.55, 129.55, 129.84, 133.24, 164.77, 178.07, 182.47 21.21, 27.95, 28.70, 29.84, 32.35, 35.10, 35.64, 43.38, 55.65, 79.85, 81.03, 87.06, 114.58, 115.61, 152.17, 153.74, 178.82, 182.67 14.16, 23.28, 23.60, 26.24, 27.98, 28.07, 28.78, 29.17, 35.20, 35.67, 35.78, 46.04, 83.48, 85.32, 86.30, 115.38, 120.84, 129.47, 158.41, 177.92, 182.85 General procedure for nucleophilic ring opening of 2,6-diazasemibullvalene 1 a with thiol derivatives 2,6-Diazasemibullvalene 1 a (0.5 mmol, 136 mg) in CH 2 Cl 2 (2 mL) was treated with 1-propanethiol (1.5 mmol, 58 mL) and the reaction mixture was stirred at rt overnight. After removal of the solvent under vacuum, purification by column chromatography (silica gel, petroleum ether/diethyl ether/triethylamine = 100:2:1) gave 3 as a colorless oil (61 %, 106 mg); 1 21.31, 22.51, 23.22, 28.02, 29.78, 31.74, 31.82, 35.46, 35.67, 37.73, 43.35, 61.18, 79.57, 81.10, 180.96, 181.08 ppm; HRMS: m/z calcd for C 21 General procedure for nucleophilic ring-opening of 1 a with carboxylic acid derivatives 2,6-Diazasemibullvalene 1 a (0.5 mmol, 136 mg) in CH 2 Cl 2 (2 mL) was treated with carboxylic acid (1.5 mmol) and the reaction mixture was stirred at room temperature overnight.…”

“…Compound 2 a: Yellow oil; 55 % (84 mg); 1 21.68, 28.00, 28.95, 30.13, 32.80, 35.32, 35.66, 43.24, 59.42, 79.82, 81.76, 92.54, 178.95, 181.16 20.87, 21.04, 27.89, 28.62, 29.69, 32.28, 35.04, 35.53, 43.35, 79.89, 81.05, 86.44, 114.88, 120.83, 129.46, 157.99, 178.54, 182.47 21.53, 22.40, 27.81, 28.20, 30.48, 32.81, 35.28, 35.61, 43.16, 79.68, 80.07, 81.92, 128.55, 129.55, 129.84, 133.24, 164.77, 178.07, 182.47 21.21, 27.95, 28.70, 29.84, 32.35, 35.10, 35.64, 43.38, 55.65, 79.85, 81.03, 87.06, 114.58, 115.61, 152.17, 153.74, 178.82, 182.67 14.16, 23.28, 23.60, 26.24, 27.98, 28.07, 28.78, 29.17, 35.20, 35.67, 35.78, 46.04, 83.48, 85.32, 86.30, 115.38, 120.84, 129.47, 158.41, 177.92, 182.85 General procedure for nucleophilic ring opening of 2,6-diazasemibullvalene 1 a with thiol derivatives 2,6-Diazasemibullvalene 1 a (0.5 mmol, 136 mg) in CH 2 Cl 2 (2 mL) was treated with 1-propanethiol (1.5 mmol, 58 mL) and the reaction mixture was stirred at rt overnight. After removal of the solvent under vacuum, purification by column chromatography (silica gel, petroleum ether/diethyl ether/triethylamine = 100:2:1) gave 3 as a colorless oil (61 %, 106 mg); 1 21.31, 22.51, 23.22, 28.02, 29.78, 31.74, 31.82, 35.46, 35.67, 37.73, 43.35, 61.18, 79.57, 81.10, 180.96, 181.08 ppm; HRMS: m/z calcd for C 21 General procedure for nucleophilic ring-opening of 1 a with carboxylic acid derivatives 2,6-Diazasemibullvalene 1 a (0.5 mmol, 136 mg) in CH 2 Cl 2 (2 mL) was treated with carboxylic acid (1.5 mmol) and the reaction mixture was stirred at room temperature overnight. After removal of the solvent under vacuum, purification by column chromatography (silica gel, petroleum ether/diethyl ether/triethylamine = 100:5: 20.55, 21.93, 22.93, 27.94, 28.38, 31.24, 33.31, 35.47, 35.67, 43.41, 80.02, 80.45, 82.08, 169.02, 177.15, 181.45 14.08, 21.08, 21.63, 22.47, 23.34, 23.37, 25.79, 26.13, 26.33, 26.60, 26.75, 26.82, 31.01, 32.90, 38.46, 38.82, 40.94, 41.18, 43.31, 79.57, 79.88, 82.01, 169.36, 177.19, 181.90 21.27, 22.26, 27.33, 27.78, 28.85, 32.52, 35.17, 35.41, 38.84, 43.21, 79.48, 79.94, 81.27, 176.63, 177.95, 182.00 ppm; HRMS: m/z calcd for C 23 21.53, 22.40, 27.81, 28.20, 30.48, 32.82, 35.28, 35.62, 43.16, 79.68, 80.01, 81.93, 128.55, 129.55, 129.85, 133.24, 164.77, 178.08, 182.47 21.75, 27.82, 28.22, 35.37, 35.66, 45.83, 55.47, 80.49, 80.65, 82.91, 113.82, 122.10, 131.82, 164.51, 163.63, 178.24, 182.91…”

“…The solvent was evaporated under vacuum to give a yellow oil, which was purified by column chromatography (silica gel, petroleum ether/diethyl ether/triethylamine = 100:3:1) to afford 5 as a yellow solid (86 %, 125 mg). 1 21.96, 27.94, 28.72, 29.70, 30.09, 33.14, 35.62, 43.72, 79.15, 80.69, 82.70, 180.85, 182.79 Nucleophilic ring opening of 1 a with a ketone in the presence of zinc triflate 2,6-Diazasemibullvalene 1 a (0.5 mmol, 136 mg) in toluene (2 mL) was treated with cyclohexanone (1.0 mmol, 100 mL) and zinc triflate (0.5 mmol, 182 mg). The reaction mixture was stirred at rt overnight.…”

“…Introduction 2,6-Diazasemibullvalene (NSBV, 1; Scheme 1) and its all-carbon analogue semibullvalene (SBV) are both structurally and chemically intriguing polycyclic strained frameworks. [1][2][3][4][5][6][7] The structural features of NSBVs include rapid intramolecular aza-Cope rearrangement, as well as a strained aziridine core, both of which have significant influence on the reaction patterns of NSBVs. [2,3] We have recently established efficient methods for the synthesis of NSBVs, which provided a good opportunity to study their structure, reaction chemistry, and synthetic applica-tion.…”

Effect of CH/P Exchange on the Fluxional Behavior of Bullvalene, Semibullvalene, and Barbaralane: A DFT Investigation

“…16 In a similar approach, the structures of aza-and phosphasemibullvalenes and barbaralanes were investigated theoretically for their possible bishomoaromatic character using correlated ab initio methods, when tetraazasemibullvalene and several phosphasemibullvalenes were found to have highly symmetric delocalized minima, possessing large negative nucleus independent chemical shift (NICS) values. 17 Following the principle of isolobal CH→BCO substitution, Schleyer and co-workers 7c showed that barrier to the degenerate Cope rearrangement was eliminated in the semibullvalenes having C2H, C4H, C6H, and C8H replaced by the BCO moieties (cf Scheme 1). In the case of barbaralanes, barbaralones and bullvalenes substituted in the 2,6-and 2,8,4,6-positions by BCO moieties, this barrier was substantially reduced.…”