title: Stereoelectronic control in regioselective carbohydrate protection.
abstract: Organotin-mediated regioselective protection has been extensively used in organic synthesis for many years. However, the mechanistic origin of the resulting regioselectivity is still not clear. By the comparison of the steric and stereoelectronic effects controlling the geometry of five-membered rings formed from neighboring group participation, from intramolecular acyl group migration, or from orthoester transesterification on pyranoside rings, a theory on the pattern resulting from the reaction with dibutyltin oxide is presented. It is thus suggested that the regioselectivity of organotin-mediated protection is controlled by analogous steric and stereoelectronic effects as in neighboring group participation and acyl group migration, mainly dependent on the stereoelectronic effects of the pyranoside itself, and not related to complex stannylene structures. An organotin protection mechanism is also suggested, emanating from steric and stereoelectronic effects, nucleophilicity, and organotin acyl migration.
authors.affiliation: School of Chemistry & Chemical Engineering, Huazhong University of Science & Technology, Luoyu Road 1037, 430074, Wuhan, P. R. China. hdong@mail.hust.edu.cn
authors.forename: Hai
authors.initials: H
authors.lastname: Dong
authors.forename: Yixuan
authors.initials: Y
authors.lastname: Zhou
authors.forename: Xiaoliang
authors.initials: X
authors.lastname: Pan
authors.forename: Fengchao
authors.initials: F
authors.lastname: Cui
authors.forename: Wei
authors.initials: W
authors.lastname: Liu
authors.forename: Jingyao
authors.initials: J
authors.lastname: Liu
authors.forename: Olof
authors.initials: O
authors.lastname: Ramström