Short and efficient synthesis of polyhydroxylated tetrahydrothiophene, tetrahydrothiopyrane and thiepane from bielectrophilic erythro, threo, xylo, ribo, arabino, manno and gluco α,ω-dibromoalditol derivatives

Polyhydroxylated tetrahydrothiophene, tetrahydrothiopyrane and thiepane rings have been readily obtained in excellent yields (78–95%) from thioheterocyclisation of the bielectrophilic peracetylated α,ω-dibrominated derivatives of tetritols (erythritol (1) and d,l-threitol (4)), pentitols (xylitol (7), ribitol (10) and d-arabinitol (14)) and hexitols (d-mannitol (17) and d-glucitol (20)), respectively. With 2,3,4,5-tetra-O-acetyl-1,6-dibromo-1,6-dideoxy-d-glucitol (21) as substrate, the unexpected 2,6-anhydro derivative 25 was obtained. This could be attributed to previous S= regioselective nucleophilic attack at C-1 position followed by 1,2-transesterification and 2,6-O-heterocyclisation. The preferential attack at C-1 of the d-glucitol derivative 21 subsequently allowed a facile direct synthesis in good yields of 2,3,4,5,6-penta-O-acetyl-1-bromo-1-deoxy-d-glucitol (26), 2,3,4,5-tetra-O-acetyl-6-bromo-6-deoxy-1-thiobutyl-1-deoxy-d-glucitol (28) and 2,3,4,5-tetra-O-acetyl-6-bromo-6-deoxy-1-thiooctyl-1-deoxy-d-glucitol (28).