Diazepinium perchlorate: a neutral catalyst for mild, solvent-free acetylation of carbohydrates and other substances

Abstract

Diazepinium perchlorate-promoted acetylation of free as well as partially protected sugars, phenols, thiophenols, thiols, other alcohols and amines is described.

Mechanistic Insight into the Cu-Catalyzed C–S Cross-Coupling of Thioacetate with Aryl Halides: A Joint Experimental–Computational Study

“…All products were characterized by 1 H NMR, 13 C NMR, and GC–MS. The following compounds are known, and their signals are in agreement with data previously reported in the literature: 1-(allyloxy)-2-iodobenzene ( 3 ), S -phenyl thioacetate ( 2 ), and S -(4-bromophenyl) thioacetate ( 6 ) …”

“…The following compounds are known, and their signals are in agreement with data previously reported in the literature: 1-(allyloxy)-2-iodobenzene (3), 33 S-phenyl thioacetate (2), 50 and S-(4-bromophenyl) thioacetate (6). 51 S-(2-(Allyloxy)phenyl) Thioacetate (4). The typical above-described procedure was followed using 1-(allyloxy)-2-iodobenzene (3, 0.5 mmol), CuI (10 mol %, 0.05 mmol), 1,10-phenanthroline (20 mol %, 0.1 mmol), and KSAc (1.5 equiv, 0.75 mmol).…”

α-Phenylthioaldehydes for the effective generation of acyl azolium and azolium enolate intermediates

“…The choice of base also influences product selectivity as the presence of DBU overrides the intrinsic selectivity of the triazolium precatalyst due to transesterification of any thiol ester product. These observations can be explained by considering mechanistic observations reported by Bode 24 and Berkessel. 5 a Bode showed that triazolylidenes bearing electron-donating N -aryl substituents (such as N -mesityl) favour azolium enolate formation, while N -aryl groups bearing electron-withdrawing substituents (C 6 F 5 or C 6 H 2 Cl 3 ) favour acyl azolium intermediates.…”

Solvent-Free Approaches in Carbohydrate Synthetic Chemistry: Role of Catalysis in Reactivity and Selectivity

“…This latter activates the electrophilic character of the acyl moiety of the Ac 2 O and can be either a protic/Lewis acid (more frequently) or a nucleophilic catalyst. Representative examples [10] of acetylation catalysts are: Dy(OTf) 3 [11], Cu(ClO 4 ) 2 [12], iodine [13], silica sulfuric acid (SSA) [14,15], DABCO (1,4-diazabicyclo[2.2.2]octane) [16], diazepinium perchlorate [17], methanesulfonic acid [18], In(OTf) 3 [19], Sm(OTf) 3 [20], Sc(OTf) 3 [21], sulfamic acid [22], and sulfonic acid functionalized nano γ-Al 2 O 3 [23]. These approaches yield peracetylation products, which in turn, are precursors for the synthesis of useful building-blocks.…”

“…As already observed, solvent-free acetylations are typically described for saccharide per-O-acetylations; however, in a few cases, it is even possible to conduct the regioselective partial acetylation of sugars by suitably adjusting the stoichiometry of acetic anhydride. With diazepinium perchlorate, acting as a mild acid activator of Ac 2 O [17], the acetylation of all free positions but the least reactive 4-OH is possible with a variety of precursors. With sulfamic acid (H 3 NSO 3 ) [22], and with triethyl orthoacetate in place of Ac 2 O, the regioselective axial O-acetylation is, in turn, possible for a cis-diol incorporated into a pyranoside system (Scheme 3).…”