Komplementär diastereoselektive Cobalt-Methylierungen des Vitamin-B12-Derivates «Cobester»
✍ Scribed by Bernahard Kräutler; Christian Caderas
- Book ID
- 102254091
- Publisher
- John Wiley and Sons
- Year
- 1984
- Tongue
- German
- Weight
- 392 KB
- Volume
- 67
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
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.