The synthesis of several novel non-benzenoid aromatic compounds by use of thiophene intermediates and annulene coupling reaction

• Main Author: Zhang, Ji
• Other Authors: Mitchell, Reginald H.
• Format: Others
• Language: English; en
• Published: 2018
• Subjects: Aromatic compounds; Nitration
• Online Access: https://dspace.library.uvic.ca//handle/1828/9795

One of the main objectives of this Thesis was to explore the use of thiophenes to synthesize several more complex aromatic systems. Thus starting from 2,4-dimethyl 5- amino-3-methylthiophene-2,4-dicarboxylate 115, the synthesis of the first cis-thia[ 13]annulene, 4-bromo-cis-9b,9c-dimethyl-9b,9c-dihydrophenyleno[1,9-bc]thiophene 116a, as well as the trans-isomer, 116b have been achieved in 11 steps. Introduction of a bromo-substituent at an early stage, facilitated rearrangement of the thiacyclophanes 119a and 119b to permit easier isolation of the product annulenes. Both the cis-thia[ 13]annulene 116a and the trans-thia[ 13]annulene 116b were found to be diatropic on the basis of their 1H NMR chemical shifts. Using thiophene dioxide 150 and 152 as key intermediates to generate multifunctional azulenes, the novel azulene containing thiacyclophane 105 has been synthesized in 9 steps. Even though this was not able to be converted to the [18]annulene 100, discovery of a new route to thiacyclophanes from thiolacetates was achieved. This has been tested successfully on a variety of other examples, including the unusual bis thiophene containing cyclophanes 194 and 195, as well as the unsymmetrical 191 which was subsequently converted to the dihydropyrene 236a and 236b. During the course of this work, we discovered a new mild method to electrophilically brominate reactive aromatics using NBS in [special characters omitted] at room temperature. This reagent was investigated for several thiophenes, azulenes and dihydropyrenes. The products from the latter were successfully coupled using Ni(0) catalysis to generate 28% of the first unsymmetrically connected dimer of DMDHP, 249, as well as 33% of the symmetrical dimer 102. Unlike 102, the bi-annulenyl 249 has a significant barrier to rotation, which is estimated as 11.0 kcal/mole from [special characters omitted] measurement, compared to a PCMODEL calculated barrier of 12 kcal/mole. This is the first measurement of the barrier to rotation in a 1,2'-binaphthyl type system. Electrophilic substitution in DMDHP using the diazonium salts 277 and 283 was also studied, and several novel cross-coupling products have been synthesized and isolated, such as 278 from 279 and 280. As well the very unusual isomeric quinones, 7-(10b, 10c-dimethyl-7-oxo- 2,7,10b, 10c-tetrahydro-2-pyrenyliden)-10b, 10c-dimethyl-2,7-10b, 10c-tetrahydro-2- pyrenone 263 and 264 have been successfully prepared by reacting 102 with NBS or PDC. Compounds 263 and 264 have highly extended conjugated systems. === Graduate