Syntheses of monohydroxy benzyl ethers of polyols: tri-O-benzylpentaerythritol and other highly benzylated derivatives of symmetrical polyols

Tin-Mediated Regioselective Benzylation and Allylation of Polyols: Applicability of a Catalytic Approach Under Solvent-Free Conditions

“…In particular, d -mannose and L -rhamnose were smoothly converted into the corresponding β-1,3-di-O-benzylated pyranoside products in high yields and short times (Table , entries 1 and 2). The β-configuration of these products points to the feasible generation of stannylene intermediates engaging the β-O-1 and O-2 sites, with the equatorial one ending up benzylated. , The high rate at 70 °C of the double benzylation may be ascribed to the facile regeneration of the 1,2-stannylene (or the 2,3-stannylene) once the first benzylation event occurs at O-3 (or O-1), as both events lead to a 2-O-bromostannylated intermediate prone to recyclization with an adjacent syn-hydoxyl . As to gluco- and galacto-configured precursors (Table , entries 3–5), the reaction mainly provided the corresponding 1,6-di-O-benzylated α-furanosides (only anomeric benzylation occurred in the case of 6-deoxy sugar fucose, entry 3).…”

“…The synthetic applications of tin acetals reported in the literature are restricted, with a few exceptions, to the selective installation of 1 to 2 benzyl groups. Examples reported in Tables – indicate that temperature plays a prominent role for tuning the extent of benzylation of polyols under catalytic solvent-free conditions, whereas the stoichiometric amount of Bu 2 SnO is mainly important in the case of conventional multistep approaches .…”

[DMAPTs]+ Cl− : A Promising Versatile Regioselective Tosyl Transfer Reagent

“…Arguably, since its first report by Shanzer and co‐workers and of all the available organo catalytic methods, organo‐stannylene acetals of glycols appeared far more superior for regioselective sulfonylation of vicinal diols in comparison to other methods due to its remarkable regio and stereoselectivities along with high yields for mono functionalization, particularly tosylation . Elaboration of this protocol for selective monofunctionalization of triols also led to the selective primary alcohol tosylation both for 1,2,6 and 1,2,4 triols, and other polyols though with slightly low levels of selectivity, compared to glycols . Interestingly, the relative stereochemistry of 1,2,4,‐triols favor the 2,4‐ anti isomer to undergo regioselective tosylation while the 2,4‐ syn isomer undergo further intramolecular 5‐ exo tet cyclization, through a twist boat like transition state, to the furan .…”