Electrochemical characterisation of 6-iodomaltose, 6 -idomaltose and 6-iodomaltoriose on a silver cathode and their one-pot electrochemical dimerization to new mixed O/C maltotetraose and maltohexaose mimics

The electrochemical reduction on silver of peracetylated 6-iodo-6-deoxy-b-maltose (2), 6-iodo-6-deoxyb-maltotriose (3) and 6'-iodo-6'-deoxyb-maltose (4) has been investigated by cyclic voltammetry and performed on a preparative scale, according to the stoichiometry, CH2IACHTUNGTRENUNG(2-4)+e!CH2C+I. In agreement with the preparative electrolysis results, cyclic voltammetry showed different profiles for the reducing terminal-iodinated 2 and 3 and for the non-reducing terminal-iodinated 4. Compounds 2 and 3 partly dimerised to maltotetraoses mimics 7 (6,6-dimer) and 8 (5',5'-dimer) in 38% overall yield and to maltohexaose mimics 12 (6,6-dimer) and 13 (5',5'-dimer) in 30% overall yield, respectively. Compounds 7 and 12 came from the dimerisation of CH2C, primary radicals at C-6, which could also abstract H-5', becoming CH3 and generating the C-5' quaternary radicals that dimerised in 8 and 13, respectively. These products were accompanied by the maltose derivatives 9, 10 and 11 a/b in 42% overall yield and bythe maltotriose derivatives 14, 15 and 16 in 48% overall yield, respectively. Compounds 9, 14 and 10, 15 came from CH2C disproportionation to CH3 and CH2=C, respectively (exocyclic double bond C-6/C-5). Compounds 11 a/b and 16 came from C-5' radical reduction, followed by acetate anion elimination