Selective Monoterpene-like Cyclization Reactions Achieved by Water Exclusion from Reactive Intermediates in a Supramolecular Catalyst

Abstract

A polyanionic supramolecular assembly (1) is shown to catalytically cyclize the monoterpene citronellal and two homologues. In contrast to cyclization in acidic aqueous solution, the hydrophobic interior of 1 prevents the capture of reactive intermediates by water. This effect was also observed in the gold-catalyzed cycloisomerization of an enyne. Due to the steric confinement of the catalyst's interior, Prins cyclizations in 1 proceed cleanly both for substrates containing and lacking gem-dimethyl substitution. Encapsulation in 1 consequently imposes a degree of mechanistic control that, similar to enzyme catalysis, is not observed in bulk aqueous solution.

Different and Often Opposing Forces Drive the Encapsulation and Multiple Exterior Binding of Charged Guests to a M4L6 Supramolecular Vessel in Water

“…The assembly contains ah ighly anionic exterior surface, which confers solubility in water,a s well as affinity for the externali on association of cationic molecules. [24] Other catalyzed chemical transformations [25,26] and dramatic changes in the properties and reactivity of encapsulatedg uest molecules [27,28] have been achieved with rate accelerationso f up twentym illion, [29] thus leadingu st oa ssume that the transition state of these reactions is stabilized, similar to the case of enzymes. For example, host 1 catalyzes the Nazarov cyclizationo f1 ,3-pentadienols with rate accelerationso f1 0 6 ,a nd this result has been attributed to transition-state binding, as well as substrate conjugate stabilization.…”

Protein-like proton exchange in a synthetic host cavity

“…Assembly 1 exhibits 12 intramolecular amide hydrogen bonds which, in analogy to structurally important peptide bonds found in polypeptides, preferentially stabilize the desired tetrahedral supramolecular structure over other conformers (35). Compound 1 and related hosts have been shown to catalyze several important chemical reactions with sizable rate accelerations (up to 10 6 ) and unusual selectivity reminiscent of enzyme catalysis (34,(36)(37)(38)(39)(40)(41). Unlike most enzymes, the reactions catalyzed by 1 are functionally and mechanistically very diverse.…”

Heterometallic transition metal clusters and cluster-supported coordination polymers derived from Tp- and Tp*-based Mo(W) sulfido precursors

“…The cage compounds, extensively studied in the last few decades by Fujita, Raymond, Nitschke and others [115][116][117][118][119][120][121][122][123][124][125][126], are a fascinating class of discrete molecular entities capable of altering molecular behavior within the confined space, and termed as 'molecular flasks' by Fujita [127]. The geometrical advantage of Tp and Tp* along with MS 3 Cu 3 (M = Mo, W) in favoring tetrahedral cages may allow us to approach other cage compounds with relative ease.…”