2-Chloro-3,4-dihydrothieno

Chloro-3,4-dihydrothieno[2,3- i ]pyrimidines (421) are prepared when the aromatic precursors 420 are treated with excess NBH over an 8-h period at room temperature. ... 

Related compound (B) has the systematic name methyl-( )-(o-chloro-phenyl)-4,5-dihydrothieno[2,3-c]pyridine-6-(7H)-acetate, hydrogen sulfate salt [2], and is a racemic residue formed during the manufacturing process. This compound may appear as a racemic mixture in samples of bulk drug substance as impurities (la) and (lb) [6, 7]. 

The action of NaBH4 on 141 (X = X = Cl) gave 2-chloro-3,4-dihydro-thieno[3,4-d]pyrimidines 142, which were used for the synthesis of 2-substituted dihydrothieno[3,4-d]pyrimidines via nucleophilic substitution reactions (81JMC376). 

By reaction of 5-chloro-2,3,6-trifluoropyridine (171) with vinylstannane 172 and monothioacetic acids (173) 5,6-difluoro-2,3-dihydrothieno[2,3-b]pyridine (174) was obtained and used as precursor for synthesis of anticancer drugs [118] (Scheme 56). 

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