Expanded Helicenes as Synthons for Chiral Macrocyclic Nanocarbons.
J Am Chem Soc
; 142(25): 11084-11091, 2020 06 24.
Article
em En
| MEDLINE
| ID: mdl-32450694
ABSTRACT
Expanded helicenes are large, structurally flexible π-frameworks that can be viewed as building blocks for more complex chiral nanocarbons. Here we report a gram-scale synthesis of an alkyne-functionalized expanded [11]helicene and its single-step transformation into two structurally and functionally distinct types of macrocyclic derivatives (1) a figure-eight dimer via alkyne metathesis (also gram scale) and (2) two arylene-bridged expanded helicenes via Zr-mediated, formal [2+2+n] cycloadditions. The phenylene-bridged helicene displays a substantially higher enantiomerization barrier (22.1 kcal/mol) than its helicene precursor (<11.9 kcal/mol), which makes this a promising strategy to access configurationally stable expanded helicenes. In contrast, the topologically distinct figure-eight retains the configurational lability of the helicene precursor. Despite its lability in solution, this compound forms homochiral single crystals. Here, the configuration is stabilized by an intricate network of two distinct yet interconnected helical superstructures. The enantiomerization mechanisms for all new compounds were probed using density functional theory, providing insight into the flexibility of the figure-eight and guidance for future synthetic modifications in pursuit of non-racemic macrocycles.
Texto completo:
1
Base de dados:
MEDLINE
Assunto principal:
Compostos Policíclicos
/
Compostos Macrocíclicos
Idioma:
En
Revista:
J Am Chem Soc
Ano de publicação:
2020
Tipo de documento:
Article
País de afiliação:
Estados Unidos