Over the last decade, we developed several strategies for the regio-and iteroselective modifications of calixarenes. As a representative example, we reported an iteroselective carbamation of calixarenes in aprotic solvents through the addition of an excess of tert-butyl isocyanate under basic conditions (Figure ). The "all-but-one" iteroselectivity was rationalized by an internal proton assisted mechanism. This mechanism involves a phenolate attacking the isocyanate and a nearby phenol to provide a proton. When only one unreacted phenolic unit remains, the absence of nearby proton donor prevents the last addition. Interestingly, unlike other examples described herein this all-but-one selective method does not lead to a specific number of iterations but depends on the number of starting reactive functions: i = m -1 for m reactive functions. The reaction was shown to work efficiently on a wide scope of substrates including parent or partially functionalized calixarenes and homooxacalixarenes (typical yields >90%). The first example of this all-but-one carbamation on p-tBucalix [6]arene with 18 equiv. of tert-butyl isocyanate showed a ite of 91% equal to the yield (Figure ). It is noteworthy that the all-but-one carbamation can also lead to regioselectivity when multiple regioisomers are possible. The all-but-one carbamation of dihomooxacalix [4]arene leads to a single regioisomer among two possibilities, thus achieving high iteroselectivity (ite of 98%, equal to the yield) and regioselectivity (Figure ).