192810-13-2Relevant articles and documents
Oligomerization of the Thiophene-Based p-Quinodimethanes 2,5-dihydrothiophene and 2-Ethylidene-5-methylene-2,5-dihydrothiophene
Trahanovsky, Walter S.,Miller, Deborah Louise,Wang, Yili
, p. 8980 - 8986 (2007/10/03)
Flash vacuum pyrolysis (FVP) of (5-methyl-2-thiophene-yl)methyl benzoate (8) produces in ca. 75% yield 2,5-dimethylene-2,3-dihydrothiophene, S-monomer (3). S-Monomer 3 is relatively stable dissolved in carbon disulfide-chloroform at -78°C. The structure of 3 is confirmed by its spectral properties. When a 0.17 M solution of S-monomer 3 was allowed to warm to room temperature, SS-dimer 5 ([2,2](2,5)thiophenophane, 14.7%), SSS-trimer 7 ([2,2,2](2,5)thiophenophane, 44.3%), and polymer were produced. A small amount ( 1%) of an SSSS-tetramer was detected by GC/MS. The mechanism proposed for the formation of these oligomers involves the combination of two molecules of 3 to give an intermediate diradical (11) that can close to form dimer 5 or react with additional molecules of 3 to form the higher oligomers. Evidence for the trapping of diradical 11 by 2,5-dimethylene-2,5-dihydrofuran (O-monomer 2) was obtained. Co-oligomerization of S-monomer 3 and O-monomer 2 gave four compounds containing the thiophene moiety: OS-dimer 16, SS-dimer 5, OSS-trimer 17, and SSS-trimer 7. Some OO-dimer 4 was produced but no OOO-trimer 6 was observed and only a trace of OOS-trimer 18 was detected. Additional support for the diradical mechanism was obtained from the study of the oligomerization of the methyl derivatives of 3, 2-ethylidene-5-methylene-2,5-dihydrothiophene (10, E and Z isomers), prepared by the FVP of (5-ethyl-2-thiophene-yl)methyl benzoate (9). Oligomerization of 10 gave several dimers and trimers including two acyclic dimers that are accounted for by intramolecular disproportionation.
