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Calix[6]arene Functionalized at Four Bridges: Conformation and Intramolecular Guest Exchange
Author(s) -
Leader Avia,
Itzhak Norbert,
Bogoslavsky Benny,
Biali Silvio E.
Publication year - 2015
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201500873
Subject(s) - chemistry , intramolecular force , conformational isomerism , calixarene , derivative (finance) , stereochemistry , crystallography , crystal structure , group (periodic table) , molecule , organic chemistry , financial economics , economics
Reaction of the tert ‐butoxycarbonyl derivative of p‐tert ‐butylcalix[6]arene ( 2 ) with excess NBS under irradiation yields a calixarene with four bromomethine bridges as the major product ( 3 ). On the basis of the number of signals in the NMR spectrum, to the product was assigned a 1,2,4,5‐substitution pattern. X‐ray crystallography indicates that the product possesses the rct 2 configuration and crystallized as a mixture of two conformers. The major form in the crystal exists in a 1,2,3‐alternate conformation where a single tert ‐butoxycarbonyl group is self‐included in the cavity and all bromines are located at equatorial positions. A rotational barrier of 18.4 kcal mol –1 was measured for the intramolecular guest exchange rotational process that involves the mutual exchange between the unique self‐included Boc group and the Boc group on the opposite ring (Boc = tert ‐butoxycarbonyl).