Synthesis and crystal structures of 2-substituted-2-phenylsulfonyloxiranes: evidence for a generalised anomeric effect in 2-phenylsulfonyloxiranesElectronic supplementary information (ESI) available: PDB files of the crystal structures of compounds 5, 6b and 7. See http://www.rsc.org/suppdata/ob/b3/b301409f/