THE REACTION OF THE ACETATES OF ALPHA-CHLORO METHYL HEMIACETALS WITH NUCLEOPHILES - SYNTHESIS OF 2-HYDROXY-1,4-DITHIANES

The acetates of the methyl hemiacetals of alpha-halo aldehydes, 1, eas ily undergo nucleophilic attack by lithium thiolates or ethane dithiol ate affording alpha-thioalkyl aldehydes 2 or 2-hydroxy-1,4-dithianes 3 , respectively. 3-monosubstituted dithianes 3 smoothly dehydrate to 2, 3-dihydro-1,4-dithiines 4, whereas 3,3-disubstituted derivatives give dimers 6. The single-crystal X-ray analysis of 6b shows that it crysta llises in a racemic form, with the dithiane ring in a chair conformati on and the exocyclic S(3) atom axially bonded to the ring. The crystal packing appears to be determined mainly by a weak C-H ... O hydrogen bonding interaction.