Important insight has been obtained into the mechanism of the reversible acid-catalysed transacetalation of cyclophane formaldehyde acetals (formals) C-i in MCI, at 25 degrees C. ne order of appearance of the lowest oligomers in the early stages of the equilibration reaction is fully consistent with ring-fusion/ring-fission processes in which oxonium ion intermediates undergo S(N)2 reactions, according to an acid-catalysed bimolecular (A2) mechanism. The alternative acid-catalysed monomolecular (A1) reaction path, based on "back-biting" processes of carbenium ions generated by S(N)1-type cleavage of oxonium ion intermediates, predicts sequences that are in marked contrast with experimental findings.
A ring-fusion/ring-fission mechanism for the metathesis reaction of macrocyclic formaldehyde acetals / Roberta, Cacciapaglia; DI STEFANO, Stefano; Mandolini, Luigi. - In: CHEMISTRY-A EUROPEAN JOURNAL. - ISSN 0947-6539. - 12:33(2006), pp. 8566-8570. [10.1002/chem.200600983]
A ring-fusion/ring-fission mechanism for the metathesis reaction of macrocyclic formaldehyde acetals
DI STEFANO, Stefano;MANDOLINI, Luigi
2006
Abstract
Important insight has been obtained into the mechanism of the reversible acid-catalysed transacetalation of cyclophane formaldehyde acetals (formals) C-i in MCI, at 25 degrees C. ne order of appearance of the lowest oligomers in the early stages of the equilibration reaction is fully consistent with ring-fusion/ring-fission processes in which oxonium ion intermediates undergo S(N)2 reactions, according to an acid-catalysed bimolecular (A2) mechanism. The alternative acid-catalysed monomolecular (A1) reaction path, based on "back-biting" processes of carbenium ions generated by S(N)1-type cleavage of oxonium ion intermediates, predicts sequences that are in marked contrast with experimental findings.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
