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Regioselective deuteriation kinetics of 2‐, 4‐, and 6‐methyl groups in D 2 O solutions of pyrylium and N‐methylpyridinium perchlorates possessing also 3‐methyl or 3‐phenyl groups
Author(s) -
Balaban Alexandru T.,
Uncuta Cornelia,
Chiraleu Filip
Publication year - 1982
Publication title -
journal of labelled compounds and radiopharmaceuticals
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.432
H-Index - 47
eISSN - 1099-1344
pISSN - 0362-4803
DOI - 10.1002/jlcr.2580190611
Subject(s) - chemistry , perchlorate , pyridinium , medicinal chemistry , regioselectivity , kinetics , pyridinium compounds , stereochemistry , salt (chemistry) , methyl group , nuclear magnetic resonance spectroscopy , group (periodic table) , organic chemistry , ion , catalysis , physics , quantum mechanics
By 1 H‐NMR it was found that 2, 3, 4, 6‐tetramethylpyrylium perchlorate (I) in D 2 O undergoes isotopic exchange at the 2, 4, and 6‐methyl groups with relative rates 5 : 40 : 1, respectively (assignments of α‐methyl NMR signals were substantiated by unambiguous synthesis). If the 3‐methyl group is replaced by a 3‐phenyl group, the relative rates for the pyrylium salt III are 2.5 : 49 : 1, respectively (in D 2 O + CD 3 OD). On the other hand, the relative rates for the 2, 4, and 6‐methyls in 1,2,4,6‐tetramethyl‐3‐phenylpyridinium perchlorate are 12 : 1 : 4, respectively (in D 2 O + CD 3 OD + NaOD). These rate differences allow the preparation of selectively deuteriated pyrylium or pyridinium salts, and of other aromatic or heterocyclic compounds starting from pyrylium salts with selectively deuteriated side‐chains.