Hydrogen bonds involving polar CH groups. Part 8. The synthesis and X-ray crystal structure of 2-(2,2-dimethyl-3-piperidinopropyl)-1,3-dithian 1,1,3,3-tetraoxide; a sterically crowded cyclic disulphone
Reaction between 2,2-dimethyl-3-piperidinopropanal (8) and lithio-2-trimethylsilyl-1,3-dithian gives a keten dithioacetal (10), which is reduced to a dithioacetal (11) with trimethylsilane in trifluoroacetic acid, and oxidised to the title compound (2) with potassium permanganate in acetic acid. The advantages of trimethylsilane as a reducing agent are discussed. Crystal structure analysis of the disulphone (2), designed as a model for intramolecular C–H N interactions, shows it to have an extended conformation, the desired cyclic conformation being disfavoured by steric effects. The structure was solved by direct methods, and refined to R 0.039 for 2 232 independent reflections. The crystals are monoclinic, a= 7.107(2), b= 25.373(4), c= 9.929(2)Å, β= 108.55(2)°, space group P21/c, and Z= 4.