Multiple competing pathways for chemical reaction: drastic reaction shortcut for the self-catalytic double-helix formation of helicene oligomers

• Published in: Chemical science (Cambridge) Vol. 8; no. 2; pp. 1414 - 1421
• Main Authors: Kushida, Yo, Saito, Nozomi, Shigeno, Masanori, Yamaguchi, Masahiko
• Format: Journal Article
• Language: English
• Published: England 2017
• Subjects: Amplification; Chemical reactions; Coiling; Competition; Conversion; Formations; Oligomers; Pathways
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/c6sc01893a

Competition among multiple pathways in a chemical reaction exhibits notable kinetic phenomena, particularly when amplification by self-catalysis is involved. A pseudoenantiomeric 1 : 1 mixture of an aminomethylene helicene ( )-tetramer and an ( )-pentamer formed enantiomeric hetero-double helices and in solution when random coil was cooled. When a solution of at 70 °C was directly cooled to 25 °C, the -to- reaction was predominant, then was slowly converted to over 60 h. The slow conversion in the -to- -to- reaction was due to the formation of the hetero-double helix , which was an off-pathway intermediate, and the slow -to- conversion. In contrast, when a solution of at 70 °C was snap-cooled to -25 °C before then maintaining the solution at 25 °C, the -to- reaction predominated, and the formation of was complete within 4 h. The reactions involve competition between the self-catalytic -to- and -to- pathways, where and catalyze the -to- and -to- reactions, respectively. Subtle differences in the initial states generated by thermal pretreatment were amplified by the self-catalytic process, which resulted in a drastic reaction shortcut.