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Molecular flasks are compounds that are able to mediate or catalyze chemical transformations inside their cavities. The development of such compounds is often inspired by nature. Enzymes, nature’s catalysts, are able to convert a certain substrate with very high turnover number and selectivity. In addition to their very high chemo-, regio-, and stereoselectivity, enzymes are also able to distinguish their substrates on the basis of size, resulting in size selectivity. To date, many synthetic materials such as metal–organic frameworks are used to accomplish size-selective transformations. However, also the number of molecular flasks known to mediate or catalyze size-selective transformations is increasing. In this perspective an overview on classic and the most recent examples of size-selective molecular flasks is given. In addition, an outlook on promising developments in cavity chemistry that may lead to the development of additional size-selective molecular flasks is given.

A system of three coupled catalytic cycles enabling the one-pot transformation of epoxides to amines via Meinwald rearrangement, imine condensation, and imine reduction is described. This assisted tandem catalysis is catalyzed by B(C6F5)3 resulting in the first tandem Meinwald rearrangement-reductive amination protocol. The reaction proceeds in nondried solvents and yields β-functionalized amines. In particular, β-diarylamines are obtained in high yields.