Supramolecular Control of the Template‐Induced Selective Photodimerization of 4‐Methyl‐7‐O‐hexylcoumarin

Abstract

A symmetric ditopic molecular receptor (3), containing two identical hydrogen-bonding recognition subunits, was designed and synthesized. These subunits are capable of binding substrates with complementary donor and acceptor sites to form a supramolecular complex through hydrogen bonding. Receptor 3 was designed to accept two guest molecules, which are held in close proximity within the supramolecular species. The substrate molecule, 4-methyl-7-O-hexylcoumarin (1 c), forms a 2:1 complex with a binding constant of 150 m(-1) for the second substrate, passing first through a 1:1 complex with an affinity constant of 510 m(-1). The orientation of two molecules of 1 c when bound to the template leads to the selective formation of the trans-syn [2+2] photoproduct 2 cB upon irradiation. Other photoproducts typically produced in the absence of the template are suppressed.

Lewis‐acid‐catalyzed Photodimerization of Coumarins and N‐methyl‐2‐quinolone

“…The product distribution can be changed by using a Pd nanocage (30). A template‐induced selective photodimerization of 4‐methyl‐7‐ O ‐hexylcoumarin has been reported (31).…”

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

“… 578 , 579 The selectivity of the [2 + 2] photodimerization was found to be altered for certain coumarins in micellar solutions 580 or in the presence of a template. 581 The enantioselective formation of coumarin dimer 317 was observed in the presence of a chiral template but with low chemical yield. 582 A racemic coumarin photodimer was employed as a probe for the mechanochemical scission within poly(methyl acrylate) polymers.…”

Exciting Supramolecular Architectures: Light‐Induced Processes and Synthetic Transformations in Noncovalent Assemblies

“…Covalent capture of a dynamic assembly around a given template often leads to the formation of a receptor for the templatea process of substrate-induced receptor synthesis. [21] Barbituric acid derivatives make convenient templates, as they possess two non-selfcomplementary binding sites that can be used to assemble photoactive chromophores, including coumarins [23] and fullerenes. [25] Reproduced with permission from ref.…”

“…[22] Similarly, Skeen et al extended this approach to promote the trans-syn photodimerization of a coumarin derivative using an extended ditopic receptor. [23] The incorporation of two or more independent binding sites and a photoactive moiety leads to systems in which different inputs can be used to control the outcome of a reaction. [24] The scope of the template approach is not limited to directing reaction pathways of well-known photochemical transformations.…”