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Polarization Effect on Regioselectivity of Pd‐Catalyzed Cyclization of 2‐Alkynylbenzaldehydes
Author(s) -
Nardangeli Nolan,
Topolovčan Nikola,
Simionescu Razvan,
Hudlický Tomáš
Publication year - 2020
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.201901203
Subject(s) - regioselectivity , chemistry , substituent , electrophile , nucleophile , catalysis , annulation , stereochemistry , double bond , triple bond , medicinal chemistry , polarization (electrochemistry) , organic chemistry
We report a study on the relationship between the polarization of C≡C bond in a series of 2‐alkynylbenzaldehydes and the regioselectivity of their Pd‐catalyzed annulation reactions. The electrophilic and nucleophilic character of the triple bond carbon atoms was examined using 13 C and HMBC NMR experiments. The direction of polarization is determined only by the formyl group and its position on an aromatic ring. On the other hand, the strength of the polarization expressed through chemical shift difference Δδ of acetylenic carbon atoms is a result of electron‐withdrawing or electron‐donating ability of the other substituent. Out of two possible regioisomers, the Pd‐catalyzed cyclization reactions of 2‐alkynylbenzaldehydes that were studied predominantly afforded 1 H ‐isochromenes suggesting that the polarization of a triple bond is one of the contributing factors in the regioselectivity of this process.