Catalysis by β‐Cyclodextrin Hydrate – Synthesis of 2,2‐Disubstituted 2H‐Chromenes in Aqueous Medium

Abstract

Ac ost-effective,o perationally simple and eco-compatible protocolf or the one-pot synthesis of photochromic pyrans by the reactiono fp ropargyl alcohols as well as propargyl ethers with differently substituted phenols under ambient atmosphere in aqueous mediumh as been developed using b-cyclodextrinh ydrate as an efficient, recyclable ands table catalyst. This is the first report where b-cyclodextrin hydrate acted as acatalyst for an organic transformation but b-cyclodextrin alone failed.

Ring opening polymerization of ε-caprolactone in the presence of wet β-cyclodextrin: effect of the operative pressure and of water molecules in the β-cyclodextrin cavity

“…Quite interestingly, a behaviour similar to that found in this study has been recently reported for the heterodomino reaction between 2-phenylbut-3-yn-2-ol and p-cresol in water at 60 C. 39 Hydrated b-CD was found to be an effective catalyst for this reaction while, dry b-CD was not active at all in spite of the fact that both compounds were dissolved in an aqueous reaction medium at reaction conditions. It is important to mention that when b-CD hydrate was dried at 130 C for 4 h, conditions at which the loss of water was complete, and added to the aqueous reaction medium, the aforementioned reaction did not occur at all.…”

“…It is important to mention that when b-CD hydrate was dried at 130 C for 4 h, conditions at which the loss of water was complete, and added to the aqueous reaction medium, the aforementioned reaction did not occur at all. 39 This behavior was attributed to a key role of water molecules inside the CD basket in the activation of the reaction. Indeed we can consider that native b-CD rapidly equilibrates with atmospheric humidity at room temperature and it is organized in a crystalline structure that at normal ambient conditions (18 C and about 50% humidity) has the composition b-CD$10.5H 2 O with about 5 water molecules between the b-CD units and about 5.5 inside the b-CD cavity.…”

Naphthopyran molecular switches and their emergent mechanochemical reactivity

“…Naphthopyrans were attained in good yields by heating an aqueous mixture of propargyl alcohol and naphthol starting materials with catalytic β-cyclodextrin hydrate. 130 In a solid state protocol, grinding a mixture of propargyl alcohol, naphthol, TsOH, and silica gel at room temperature with a mortar and pestle produced the corresponding naphthopyrans, albeit in poor to moderate yields ( Scheme 9 ). 109 Substantial improvements were achieved using ball-milling and catalytic InCl 3 leading to naphthopyran formation in excellent yields with minimal side products.…”