Thermal and Photochemical Switching of Chiral Sugar Azoalkenes: A Mechanistic Interrogation. Issue 19 (11th May 2020)

• Record Type: Journal Article
• Authors: Sánchez‐León, Ana María; Cintas, Pedro; Light, Mark E.; Palacios, Juan Carlos
• Is Part Of: European journal of organic chemistry. Issue 19(2020)
• Page Start: 2827
• Page End: 2841
• Publication Date: 2020-05-11
• Subjects: Azoalkene -- Carbohydrates -- Chirality -- Photoswitching -- Thermal isomerization; Chemistry, Organic -- Periodicals; Organic compounds -- Synthesis -- Periodicals; Bioorganic chemistry -- Periodicals; Chemistry, Physical organic -- Periodicals; 547
• DOI: 10.1002/ejoc.202000029
• Languages: English
• ISSNs: 1434-193X

Abstract

Abstract : This manuscript describes a thorough study on the thermal and photochemical evolution of carbohydrate‐based azoalkenes, which have been proposed as putative intermediates en route to other heterocyclic derivatives and nucleoside analogues. These substances represent new protagonists in the azo chemical space, under intense study due to reversible photoswitching of this functional group suitable for designing artificial nanomachines and responsive materials. Although structurally simple azadienes derived from monosaccharides have long been known, the dynamics of such species in solution and solid phase remains poorly characterized. Herein, we show that such azoalkenes undergo 3 E →3 Z thermal isomerization, which is accelerated by the presence of Brönsted acids. On the other hand, they undergo 1 E →1 Z isomerization when irradiated by sunlight, while the reverse 1 Z →1 E isomerization occurs thermally in the dark or under acid catalysis. As a result, sugar monoazadienes not only exhibit inherent chirality, but also dual on‐off isomerization under external stimuli. Both experiments and DFT‐based computational analyses provide a consistent and unifying mechanistic picture of these transformations. Abstract : Incorporation of the photolabile azo group into an unsaturated sugar chain affords a class of glycomimetics susceptible of thermal and photo‐induced switches under mild conditions (sunlight irradiation). Herein, such stereomutations and mechanistic routes are disentangled by experiment and DFT calculations.