DFT calculations on the protonation of two 1,3-butadiyne units fixed in medium-sized rings

• Verfasst von: Esser, Birgit [VerfasserIn]
• Verfasst von: Gleiter, Rolf [VerfasserIn]
• Titel: DFT calculations on the protonation of two 1,3-butadiyne units fixed in medium-sized rings
• Verf.angabe: Birgit Esser and Rolf Gleiter
• E-Jahr: 2006
• Jahr: June 6, 2006
• Umfang: 10 S.
• Fussnoten: Gesehen am 16.10.2017
• Titel Quelle: Enthalten in: The journal of organic chemistry
• Ort Quelle: [S.l.] : American Chemical Society, 1936
• Jahr Quelle: 2006
• Band/Heft Quelle: 71(2006), 14, Seite 5126-5135
• ISSN Quelle: 1520-6904
• DOI: doi:10.1021/jo060426h
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1564444988

Abstract

The N-bis-protonated forms of 1-azacyclotetradeca-3,5,10,12-tetrayne (19) and 1,8-diazacyclotetradeca-3,5,10,12-tetrayne (20) were used as model systems to study the HCl addition to two 1,3-butadiyne units in close proximity using quantum chemical means. The model calculations were carried out mainly at the B3LYP/3-21G or 6-31G* level. The basis set 6-311G* was used for single-point calculations. The calculations reveal that 19 and 20 are preferably protonated at the C4 center accompanied by a transannular ring closure between C3 and C13 yielding the bicyclic systems 23 and 24, respectively. Further stabilization of these vinyl cations is achieved by a second transannular ring closure between C6 and C10 leading to the 5−8−5 tricyclic systems 27 and 28, which are further stabilized by the addition of a chloride anion. The different regiochemistry experimentally observed for 13b and 16b was rationalized by calculating local softness parameters. The observed product selectivities for the formation of 14b and 15b were traced back to the relative stabilities of the primary protonation products 23 and 24, respectively. Model calculations on 1-azacyclopentadeca-3,5,11,13-tetrayne (65) and 1-azacyclohexa-deca-3,5,12,14-tetrayne (66) as examples for medium-sized rings with nonparallel 1,3-butadiyne units revealed a concerted process of protonation and C3−C15 (65) or C3−C16 (66) ring closure. The second step is the formation of an aromatic central ring as a result of a ring closure between C6−C13 and C6−C14, respectively.