Exploring the Activation Modes of a Rotaxane-Based Switchable Organocatalyst

Abstract

The reactivity of a rotaxane that acts as an aminocatalyst for the functionalization of carbonyl compounds through HOMO and LUMO activation pathways has been studied. Its catalytic activity is explored for C-C and C-S bond forming reactions through iminium catalysis, in nucleophilic substitutions and additions through enamine intermediates, in Diels-Alder reactions via trienamine catalysis, and in a tandem iminium-ion/enamine reaction. The catalyst can be switched "on" or "off", effectively controlling the rate of all of these chemical transformations, by the in situ change of the position of the macrocycle between two different binding sites on the rotaxane thread.

Wholly Synthetic Molecular Machines

“…In the case of the molecular shuttle, the easiest way to confer bistability is to incorporate two (very) different recognition sites onto the axle of the dumbbell component of a [ 2]rotaxane ( Figure 4b). [85] This objective can be achieved by replacingt he hydroquinone recognition sites in the moleculars huttle by tetrathiafulvalene and 1,5-dioxynaphthaleneu nits, [86] as strong and weakr ecognition sites, respectively,i nawide range of donor-acceptor rotaxanes and catenanes that have found applicationi nc atalysis, [87][88][89] molecular electronic devices [90,91] and drug delivery systems. [92] Figure 3.…”

“…Based on the flood of reviews [24-27, 58, 63, 89, 118, 121] and feature articles, [147,148] not to mention remarkable, high-profile papers [43,53,56,61,87,88,94,108,112,128,135,136,144,146] and news & views, [95,129,137,145] that have surfaced in the scientific literature which enjoyg lamour status duringt he past couple of years, research into wholly synthetic molecular machines appearst o have reached at ippingp oint. If this point in the rise of molecular machines [24,25] has indeed been reached, then the questions which arise are what next and where next?T he latter question is the easier of the two to answer:i ft he history of science tells us anything, it is that applications which find their way into our everyday lives are ap rerequisite for the recognition of an ew field of science.…”

Dynamic Responsive Systems for Catalytic Function

“…In its protonated form, the macrocyclic ring blocks the secondary amine and no conversion was observed over five days; upon treatment of the system with sodium hydroxide, complete conversion is achieved within one hour. The authors have also demonstrated the scope of catalyst 121 in a range of reactions catalyzed by iminium (β‐sulfenylation of α,β‐ unsaturated carbonyl compounds, Michael addition of methylene compounds to α,β‐ unsaturated aldehydes) and enamine (α‐chlorination of aldehydes and Michael addition of aldehydes to vinyl bissulfone) reactivity platforms, as well as in tandem iminium‐enamine and trienamine catalysis (Diels–Alder reaction between 2,4‐dienal 135 ) and cyanoester 136 . In iminium catalysis, high conversions with the ON state are observed, but the OFF state displayed some background activity for more activated substrates.…”

Bifunctional Molecular Photoswitches Based on Overcrowded Alkenes for Dynamic Control of Catalytic Activity in Michael Addition Reactions

“…Notably, these two pairs of catalytic functional groups would also be addressed with two opposite helical chirality, P or M , upon irradiation and thermal relaxation. We envisioned such a design as a feasible future route for stimuli‐responsive switchable catalysts in multi‐tasking systems and one‐pot multi‐step diastereo‐ and enantioselective reactions …”