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Prediction by 13 C NMR of regioselectivity in 1,3‐dipolar cycloadditions of acridin‐9‐yl dipolarophiles
Author(s) -
Vilková Mária,
Ungvarská Maľučká Lucia,
Imrich Ján
Publication year - 2016
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.4307
Subject(s) - regioselectivity , chemistry , structural isomer , acridine , stereochemistry , carbon 13 nmr , medicinal chemistry , nuclear magnetic resonance spectroscopy , acridine derivatives , organic chemistry , catalysis
Strong correlation was found between 13 C NMR chemical shifts of dipolarophilic CHCH carbons and regioselectivity in 1,3‐dipolar cycloadditions of new acridin‐9‐yl dipolarophiles with stable benzonitrile oxides (BNO). Accordingly, two starting dipolarophiles, (acridin‐9‐yl)‐CHCH‐R (R = COOCH 3 or Ph), reacted with three BNOs (2,4,6‐trimethoxy, 2,4,6‐trimethyl, and 2,6‐dichloro) to give a mixture of two target isoxazoline regioisomers in which the acridine was bound either to isoxazoline C‐4 carbon (4‐Acr) or C‐5 one (5‐Acr). Methyl 3‐(acridin‐9‐yl)propenoate afforded major 4‐(acridin‐9‐yl)‐isoxazoline‐5‐carboxylates (4‐Acr) and minor 5‐(acridin‐9‐yl)‐4‐carboxylates (5‐Acr). 9‐(2‐Styryl)acridine regiospecifically afforded only 4‐Acr cycloadducts. The ratios of regioisomers were compared with analogous reactions of acridin‐4‐yl dipolarophiles. Regioselectivity was dependent on a polarity of the CHCH bond, donor effects in BNO, and stabilization by stacking of aromatic substituents in the products. Copyright © 2015 John Wiley & Sons, Ltd.