Kobalt‐katalysiert Cycloadditionen von Alkinen und Nitrilen zu Pyridinen: Ein neuer Zugang zu Pyridoxin (Vitamin B₆)

Abstract

Cobalt‐Catalyzed Cycloaddition of Alkynes and Nitriles to Pyridines: A New Route to Pyridoxine (Vitamin B 6 ) A new synthesis of pyridoxine hydrochloride ( 1 ) based on a Co‐catalyzed cycloaddition of MeCN with substituted di(2‐propynyl) ethers ( 3 and 16 ) is described. The reaction sequences following cycloaddition and leading to 1 involve as key steps the rearrangement f the pyridine‐ N ‐oxide 6 to the 3‐hydroxypyridine 7 with Ac 2 O and a modified Curtius rearrangement of the acid 19 and subsequent diazotation and hydrolysis to the same pyridoxine precursor 7 , respectively. The intermediate 7 is transformed to 1 by well‐known procedures.