Extraannular fluorinated calixarenes: Regiospecificity of the deoxofluorination reactions of bis(spirodienol) derivatives

A new route for the partial displacement of OH groups of p-tert-butylcalixa rene via spirodienol derivatives is described. NaBH4 reduction of the bis(s pirodienone) calixarene derivatives 2a-2c afforded the corresponding bis(sp irodienols) 3a-3c in stereospecific fashion. H-1 NMR NOESY spectroscopy ind icated that in the case of 2a, the reaction proceeds by attack at the exo f ace of the two carbonyls (the face located anti to the spiro C-O bond). The spirodienols readily revert to p-tert-butylcalix[4]arene when heated. The reaction of 3a with the deoxofluorinating agent DAST (Et2NSF3) afforded a m ixture of extraannular substituted calixarenes possessing one or two fluoro -substituted dehydroxylated rings. The bisfluorinated calixarene 6a adopts in the crystal a conformation (1,3-alternate) similar to that adopted in so lution by the di-dehydroxylated calixarene 6b. An experiment conducted with a selectively deuterated spirodienol derivative indicated that the deoxofl uorination reaction involves regiospecific nucleophilic attack at the gamma position of the pentadienol subunit.