Reaction of dibutyltin oxide with amides in presence of traces of water: multinuclear NMR study and mechanism

The product of the reaction of primary and secondary amides with dibutyltin oxide is shown to be a dimeric 1,3-diacyloxytetrabutyldistannoxane. The re action was studied in hulk with model amides at 180 degrees C, avoiding per fect anhydrous conditions, in view to be transposable to transamidification with reactive extrusion process. The formation of an intermediate compound of the type 1-acyloxy-3-alkylaminotetrabutyldistannoxane is pointed out. W ith an excess of amide, the presence of water leads to the dimeric 1,3-diac yloxytetrabutyldistannoxane. Without an excess of amide, the hydrolysis of this intermediate leads to a more complex tetrastannoxane structure associa ted in a more or less perfect ladder-like structure including partially hyd rolyzed and condensed forms of the distannoxane. The dimeric 1-acyloxy-3-al koxytetrabutyldistannoxane resulting from the reaction of esters with dibut yltin oxide are shown to give a similar stannoxane structure after hydrolys is. All the products were characterized in solution by H-1-, C-13- and Sn-1 19-NMR spectroscopy. On the basis of the spectroscopic analysis, a mechanis m of the reaction is proposed and discussed. (C) 1999 Elsevier Science S.A. All rights reserved.