Cyclocondensation of 2-lithiomethylthiazoles and 2-lithiomethylthiazoline with α-oxoketene dithioacetals: synthesis of substituted and annelated thiazolo- and dihydrothiazolo[3,2-a]pyridinium compounds

Volume 46, Issue 12, 1990, Pages 4295–4302

  • Department of Chemistry, North-Eastern Hill University, Shillong 793 003, Meghalaya India,

The oxoketene dithioacetals  undergo regioselective 1,2-addition with 2-lithiomethyl-4-methylthiazole and 2-lithiomethylthiazoline (3) to afford the carbinol acetals  which on borontrifluoride etherate assisted cyclization yield the corresponding substituted and annelated 3-methyl-5- methylthiothiazolo[3,2-a.] pyridinium tetrafluoroborates  and the dihydro derivatives respectively in good yields. The corresponding 2-methyl-5-phenylthiazole however underwent both nuclear and side chain deprotonation and yielded a mixture of products under similar reaction conditions.