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Rotation‐Locked 2,6‐Pyrido‐allenophanes: Characterization of all Stereoisomers
Author(s) -
Lahoz Inmaculada R.,
NavarroVázquez Armando,
LlamasSaiz Antonio L.,
AlonsoGómez José Lorenzo,
Cid M. Magdalena
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201201186
Subject(s) - diastereomer , sonogashira coupling , chemistry , circular dichroism , molecule , crystal structure , stereochemistry , optical rotation , intermolecular force , crystallography , atropisomer , catalysis , organic chemistry , palladium
New 2,6‐disubstituted pyrido‐allenophanes with locked rotation of aromatic spacers were designed and synthesized. The synthesis was accomplished by Pd‐catalyzed C(sp 2 )–C(sp) Sonogashira cross‐coupling reaction between 1,3‐diethynylallene (DEA) and 2,6‐dibromopyridine followed by an intermolecular ring closure. Because racemic DEA was employed, pyrido‐allenophanes were obtained as mixtures of stereoisomers that were resolved by preparative HPLC. The conformational space of all these diastereoisomers was explored at the CAM‐B3LYP/6‐31+G*//AM1 level of theory. The isomers were characterized through their symmetry properties revealed in NMR, circular dichroism, and chiral stationary‐phase HPLC experiments. X‐ray diffraction was used to assign and to corroborate the configuration of several diastereoisomers. The unexpected encapsulation of two molecules of CHCl 3 in the crystal structures shows the potential of these conformationally hampered allenophanes as encapsulating hosts.