Catalytic, Regioselective Sulfonylation of Carbohydrates with Dibutyltin Oxide under Solvent-Free Conditions

Abstract

A simple approach was developed for the solvent-free regioselective functionalization of carbohydrate polyols with 4-toluesulfonyl (tosyl) group, allowing the easy and quick activation of a saccharide site with a tosylate leaving group. The method is based on the use of catalytic dibutyltin oxide and tetrabuylammonium bromide (TBAB), and a moderate excess of N,N-diisopropylethyl amine (DIPEA) and tosyl chloride (TsCl), leading to the selective functionalization at 75 °C of a secondary equatorial hydroxy function flanked by an axial one in a pyranoside. The procedure is endowed with several advantages, such as the use of cheap reagents, experimental simplicity, and the need for reduced reaction times in comparison with other known approaches.

Effective Organotin-Mediated Regioselective Functionalization of Unprotected Carbohydrates

“…Recently, Dong and co-workers reported the iron-catalyzed regioselective sulfonylation and acylation of polyols, which utilized acyl acetone ligands with an electron-withdrawing group at one end and an electron-donating group at the other end (Scheme e) . The regioselective functionalization of cis -1,2-diols and trans- 1,2-diols , has also been demonstrated under catalytic conditions. However, despite the advances in the development of catalytic organotin-mediated reactions, there is still lack of a general method applicable to unprotected sugars, perhaps due to the various hydroxyl group orientations that may change the structure of the stannylene complex and thus affect the selectivity.…”

“…Since tosylation is much slower than benzoylation, a nucleophilic catalyst such as 4-dimethylaminopyridine (DMAP) is required to ensure that the reaction reaches completion . It is known that selective tosylation has been developed and practiced for decades, , and tosylated carbohydrates have been used for the synthesis of biologically important derivatives . However, using tetrabutylammonium bromide (TBAB) in the preactivation mode, the synthesis of a series of mono-tosylated sugars has been demonstrated more efficiently and regioselectively.…”

Stearoyl Glucopyranosides: Selective Synthesis, PASS Analysis, In Vitro Antimicrobial, and SAR Study

“…However, sugars especially monosaccharide molecules contain several hydroxyl groups of similar reactivity and for this reason; selective acylation of monosaccharide derivatives is a prominent challenge in the field of carbohydrate chemistry. For efficient selectivity of monosaccharide derivatives direct acylation [22,23], protection-deprotection technique [24,25], organotin (bistributyltin oxide or dibutyltin oxide) mediated regioselective acylation [26,27] methods are used successfully. Considering the benefits of methods, especially our target, the direct acylation technique produces a relatively better yield compared to other techniques.…”