A New Convergent Synthesis of Thiamine Hydrochloride

Thiamine hydrochloride (1a; 3-[(4-amino-2-methylpyrimidin-5-yl)methyl]-5-(2-hydroxyethyl)-4-methylthia-zolium chloride hydrochloride; vitamin B1) has been synthesized in excellent yield by condensation of 3-mercapto-4-oxopentyl acetate (5a) with 3, 4-dihydro-7-methylpyrimido[4, 5-d]pyrimidine (4) in formic acid. The two intermediates 5a and 4 are prepared from 3-chloro-4-oxopentyl acetate (3) and 4-amino-2-methyl-5-(aminomethyl)-pyrimidine (Grewe diamine; 2a), respectively.