Reductive deoxygenation of ortho-hydroxyaromatic aldehydes to 1,2-bis(hydroxyaryl)ethanes: application to the synthesis of ethylene bridged calixarene-analogous metacyclophanes

Cooperative Al(Salen)-Pyridinium Catalysts for the Asymmetric Synthesis of trans-Configured β-Lactones by [2+2]-Cyclocondensation of Acylbromides and Aldehydes: Investigation of Pyridinium Substituent Effects

“…Based on our previously established protocol [ 53 , 54 ] the ligands 14 could be prepared via a general 4-step procedure ( Scheme 3 ). Phenols 9 were formylated with paraformaldehyde in the presence of NEt 3 and MgCl 2 [ 72 , 73 ]. A subsequent bromomethylation of 10 with paraformaldehyde, HBr and catalytic amounts of sulfuric acid gave benzyl bromides 11 in high yields [ 74 ].…”

Titanium Salen Complexes with Appended Silver NHC Groups as Nucleophilic Carbene Reservoir for Cooperative Asymmetric Lewis Acid/NHC Catalysis

“…However, depending on the reaction conditions also a known γ-lactone could be formed in good yields using this Ag-carbene route, which might thus be an interesting alternative compared to the common imidazolium salt/base approaches. 4147 precursors and ligands were prepared according to literature procedures: 1-mesityl-1H-imidazole, [31] 4-mesityl-4H-1,2,4-triazole, [32] 4-phenyl-4H-1,2,4-triazole, [33] 1-phenyl-1H-benzo [d]imidazole, [34] 1-mesityl-1H-benzo [d]imidazole, [35] (1R,2R)-N1-mesityl-1,2-diphenylethane-1,2-diamine, [36] 5-tert-butyl-2-hydroxybenzaldehyde 1, [37] 5-(tert-butyl)-3-(halomethyl)-2-hydroxybenzaldehydes 2, [8] [7a] (1R,2R)-1,2-bis(4methoxyphenyl)ethane-1,2-diamine, [38] (1R,2R)-1,2-dicyclohexylethane-1,2-diamine, [39] [6] and (R,R)-(-)-N,N′-bis{5-tert-butyl-3-[(1mesityl-1H-imidazol-3-ium)-1-ylmethyl]salicylidene}-1,2-cyclohexanediamine dichloride (4j). [7a] All other laboratory chemicals were purchased from commercial suppliers and were used without purification unless otherwise indicated.…”

Calixarenes containing modified meso bridges

“…This fact is promising for their use in supramolecular chemistry. 62 Another example of a homocalixarene is 19, obtained from diphenylmethane dialdehyde 20 using aluminum powder and sodium hydroxide. 63 Compound 19 has proven useful as a synthon for further reactions.…”

“…62 The reaction of 15a afforded two homocalixarenes, 16a and 17, which were separated by column chromatography. In the case of KOH, RbOH and CsOH, 16a is the major product, while in the presence of LiOH or NaOH, 17 prevails.…”