SiO₂-Supported CeCl₃·7H₂O−NaI Lewis Acid Promoter:  Investigation into the Garcia Gonzalez Reaction in Solvent-Free Conditions^⊥

Abstract

The Knoevenagel condensation of aldose sugars with beta-dicarbonyl compounds produces furan derivatives having polyhydroxyalkylated alkyl side chains; this reaction is known as the Garcia Gonzalez reaction. Despite the fact that these polyhydroxyalkyl furans are interesting scaffolds for synthetic chemists to utilize in the synthesis of a variety of biologically interesting molecules, the reported approach suffers from harsh conditions. The development of a general and more efficient protocol is of considerable importance, and in this manuscript, we wish to explore the role of the NaI in enhancing the activity of CeCl3.7H2O as a useful water-tolerant Lewis acid promoter for the Garcia Gonzalez reaction. The procedure proceeds with good yields at 50 degrees C using our system supported on SiO2 in solvent-free conditions and represents a simple and convenient methodology for the preparation of densely functionalized molecules. Furthermore, the first qualitative results obtained on mechanistic investigation on the role of iodide on this our heterogeneous reaction may be of value for optimization of existing organic transformations and for the development of new ones.

Electron impact ion fragmentation pathways of peracetylated C‐glycoside ketones derived from cyclic 1,3‐diketones

“…This paper presents the analysis of products obtained from the mild base‐catalyzed condensation of cyclic β ‐diketones with representative isotopically labeled aldose sugars. The reaction products and their peracetylated analogs conform to the expected structures 1 and 2 (Scheme ) and there is no evidence of previously reported ketofurans that are obtained with Lewis acid catalysts 9–13. The EI‐generated ion fragmentation pathways deduced from the analysis are presented and discussed with respect to our earlier work 2…”

An Efficient Catalytic Method for Regioselective Sulfenylation of Electron‐Rich Aza‐Aromatics at Room Temperature

“…Undoubtedly, the presence of NaI is essential for the efficient preparation of 3‐sulfenylindole 3aa by our methodology, but all previous efforts to structurally characterize our CeCl 3 · 7H 2 O/NaI system have been unsuccessful. For a possible understanding of the mechanistic role of NaI, we analyzed the interaction between CeCl 3 · 7H 2 O and NaI by X‐ray Photoelectron Spectroscopy (XPS) 27. The CeCl 3 · 7H 2 O/NaI system was treated with acetonitrile for 4 h at room temperature, and then the solvent was removed by rotary evaporation and the resulting mixture was analyzed.…”

New Methodology for the Stereoselective Synthesis of α‐Furfurylamines from Sugars: Application to the Synthesis of Furyl Amino Acids and 3‐Furylisoserines

“…Recently, it has been described that condensation between hexoses and ethyl acetoacetate catalyzed by CeCl 3 /NaI/SiO 2 under solvent‐free conditions at 50 °C affords tetrahydroxybutylfurans in good yields 13. This method is an efficient alternative to the classical García–González reaction, where this condensation is catalyzed by ZnCl 2 in EtOH as solvent 14.…”