Synthesis and Hydrogenolysis of Dioxolane-Type Diphenyl-Methylene and Fluoren-9-Ylidene Carbohydrate Acetals Containing a Neighbouring Substituted Hydroxyl Function

Synthesis, regioselective hydrogenolysis, partial hydrogenation, and conformational study of dioxane and dioxolane-type (9′-anthracenyl)methylene acetals of sugars

“…However, an opposite directing effect of the free OH-4 next to the acetal ring also appears and gives rise to the formation of the axial ether 20. We demonstrated earlier 15,16 in the course of symmetrical acetals of sugars that an adjacent-free hydroxyl could participate in the opening reaction of the acetal ring. Being a free hydroxyl present at the acetal derivative first the reagents reacted with the OH free forming an aluminate derivative, then the cleavage of the acetal occurred through an intramolecular complexation of the adjacent oxygen of the acetal ring.…”

Quantum chemical studies on the partial hydrogenolysis of methyl 2,3-O-diphenylmethylene-α-l-rhamnopyranoside

“…Previous assumption on the mechanism of partial hydrogenolysis 6 Geometry optimizations of 2 consistently lead to a structure in which the Al was strongly associated to O3. In fact, this association featured both minima found from relaxed rotation around the O4-Al bond.…”

“…In this study we consider this molecule as the "product" since the subsequent step is hydrolysis which needs the addition of water and is separated in time, as well. 6 This Letter deals with the "reactant" (2a)…”

“…The reaction of methyl 2,3-O-diphenylmethylene--Lrhamnopyranoside derivatives with chloroalane in Et 2 O : CH 2 Cl 2 1 : 1 has been studied by our research group. 6 At the 4-OH derivative only the 2-O-diphenylmethyl product was formed, while in the 4-OMe or 4-deoxy cases the reaction resulted in a mixture of 2-O-and 3-O-ethers, where the latter were the major products. A schematic reaction mechanism was proposed for compound 1 possessing a free hydroxy group at position 4, 6 in which initially a 4-O-chloroalane derivative 2 forms then opening of the dioxolane ring takes place, and finally 3 is hydrolyzed to give 4 (Scheme 1).…”

A kinetic study on the reductive opening of the diphenylmethylene acetal in methyl 2,3-O-diphenylmethylene-α-l-rhamnopyranoside

“…chloroalane) in Et 2 O/CH 2 Cl 2 1:1. 11 While at the 4-unsubstituted derivative (1) only the 2-Odiphenylmethyl product was formed, at the 4-OMe or the 4-deoxy cases the reaction resulted in a mixture of 2-O-and 3-O-benzyl ethers, where the latter ones were the major products. In the 4unsubstituted case a schematic reaction mechanism was proposed in which first a 4-O-chloroalane derivative (2) forms, followed by the opening of the dioxolane ring, and finally 3 is hydrolyzed by addition of water (Scheme 1).…”