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Komplementär diastereoselektive Cobalt‐Methylierungen des Vitamin‐B 12 ‐Derivates «Cobester»
Author(s) -
Kräutler Bernahard,
Caderas Christian
Publication year - 1984
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19840670727
Subject(s) - chemistry , alkylation , perchlorate , methyl iodide , toluene , yield (engineering) , cobalt , selectivity , medicinal chemistry , iodide , methylation , nitration , chloroform , derivative (finance) , stereochemistry , catalysis , organic chemistry , ion , biochemistry , materials science , metallurgy , gene , economics , financial economics
Complementary Diastereoselective Cobalt Methylations of the Vitamin‐B 12 Derivative Cobester Treatment of heptamethyl cob(I)yrinate ( 2 ) in toluene/tetrahydrofurane ( ca . 4:1) with methyl p ‐toluenesulfonate under exclusion of O 2 and with protection from light leads to the selective formation of the heptamethyl Co β‐methylcob(III)yrinate (perchlorate 1b ) in 75% yield. In contrast, methylation of 2 with methyl iodide under the same conditons results in the isomeric heptamethyl Co α‐methyulcob(III)yrinate (perchlorate 1a ) in 73% yield, besides 7% of 1b . This complementary diastereoface‐selectivity of the methylation at the Co‐center results from alkylation under kinetic control and apparently involves two mechanistically distinct alkylation processes. A radical mechanism is considered to account for the stereochemically unusual outcome of the reaction with methyl iodide.