NMR data for 90+ natural sesquiterpenes possessing triquinane cores were examined with the help of a relatively fast parametric/DFT hybrid computational method, DU8+. Thirteen of these compounds, i.e., approximately 14% of the sample, required structure correction. This rate of misassignment is similar to the percentage of misassigned halogenated sesquiterpenes reported previously.

NMR data for natural products containing the epoxy moiety have been revisited and reanalyzed with the help of a recently developed parametric/DFT hybrid computational method, DU8+. More than 20 structures needed revision, which points to challenges in NMR solution structure assignment for molecules possessing this structural feature. Among the revised structures are achicretin 2, acremine P, aromaticane I, artanomalide B, botryosphaerihydrofuran, chloroklotzchin, crithmifolide, crotodichogamoin A, emervaridone C, 9α,15-epoxyafricanane, fischambiguine B, grandilobalide B, guaianolide A, guatterfriesols A and B, juncenolide G, roscotane D, secoafricane 7, taccalonolides AJ and AF, and related compounds.

Graphical abstract

A new method for photoinduced dearomatization of arenes via an intramolecular cycloaddition with aza-o-xylylenes generated by the excited-state intramolecular proton transfer (ESIPT) in the readily available photoprecursors is developed. The topology of this cycloaddition, [2+4], is unprecedented for photo-dearomatizations of benzenoid aromatic carbocycles. It provides rapid access to novel heterocycles, cyclohexadieno-oxazolidino-quinolinols, as valuable synthons for a broad range of postphotochemical transformations.

Atom- and step-economy in photoassisted diversity-oriented synthesis (DOS) is achieved with a versatile oxalyl linker offering rapid access to complex alkaloid mimics in very few experimentally simple steps: (i) it allows for fast tethering of the photoactive core to the unsaturated pendants, especially important in the case of (hetero)aromatic amines-essentially a one-pot reaction with no isolation of intermediates; (ii) the α-dicarbonyl tether acts as a chromophore enhancer, extending the conjugation chain and facilitating the "harvest" of the lower energy photons for the primary and secondary photoreactions; (iii) it enhances the quantum yield of intersystem crossing (ISC), i.e., it is capable of sensitizing secondary photochemical processes in the cascade; and (iv) the tether forms an additional heterocyclic moiety, imidazolidine-4,5-dione, a known pharmacophore. The overall photoassisted cascade is an efficient complexity-building process as quantified by computed step-normalized complexity indices, leading to extended polyheterocyclic molecular architectures comparable in complexity to natural products such as paclitaxel while requiring only 2-4 simple synthetic steps from readily available chemical feedstock.