Preparation of glycoluril monomers for expanded cucurbit[n]uril synthesis

Glycoluril derivatives bearing free ureidyl groups () and bis(cyclic ethers) () are the fundamental building blocks for the synthesis of cucurbituril, its derivatives, and its congeners. The known derivatives of and fall into two main classes—those bearing alkyl or aryl functional groups on their convex face. In this paper we present a third class of glycolurils, namely those bearing substituents that are electron withdrawing in character. This class of compounds carries carboxylic acid derived functional groups on their convex face and are derived from diesters and . An improved synthesis of and is reported and their modification described. For example, and are converted into secondary amides () by heating in solutions of the neat primary amines. The secondary amides can be transformed into imides (, , ) by heating with PTSA in ClCH2CH2Cl. The isolation of these compounds in pure form in high yields is accomplished by simple and scalable washing or recrystallization procedures. We also present the X-ray crystallographic characterization of bis(cyclic ethers) , , and . We anticipate that the ready availability of ester, carboxylate, acid, secondary amide, imide, and tertiary amide derivatives of and will expand the scope of the synthesis of cucurbituril derivatives by providing a new class of building blocks with electron withdrawing substituents.