Consecutive π-Lewis acidic metal-catalysed cyclisation/photochemical radical addition promoted by generated 2-benzopyrylium as the photoredox catalyst.

A π-Lewis acidic metal-catalysed cyclisation/photochemical radical addition sequence was developed, which utilises generated 2-benzopyrylium cation intermediates as photoredox catalysts and electrophilic substrates to form 1-isochromene derivatives in good yields in most cases. The key 2-benzopyrylium intermediates were generated through the activation of the alkyne moiety of -carbonyl alkynylbenzene derivatives by such π-Lewis acidic metal catalysts as AgNTf and Cu(NTf), and the subsequent intramolecular cyclisation and proto-demetalation using trifluoroacetic acid. Further photo-excitation of the 2-benzopyrylium intermediates facilitated single-electron transfer from a benzyltrimethylsilane derivative as a donor molecule to promote the radical addition of arylmethyl radicals to the 2-benzopyrylium intermediates.

Intermolecular -selective Diels-Alder reaction catalysed by dual-functional Brønsted acid: conformational restriction of transition states by hydrogen bonds as the key interaction.

An -selective Diels-Alder (-DA) reaction in which the formed diastereomer is different from that formed in the conventional -selective Diels-Alder (-DA) reaction was developed, which involves a dual-functional Brønsted acid as a catalyst and not only a dienophile (vinylquinoline) but also an acyclic diene (dienylcarbamate) having a sterically less demanding substituent. Factors necessary for achieving the -DA reaction were extracted through an exhaustive computational search of the corresponding transition states, in which the relative orientation of the dienophile and the acyclic diene is firmly defined by hydrogen bonding interactions with a dual-functional Brønsted acid catalyst. It was experimentally verified that the combined use of the dual-functional acid catalyst, such as phosphoric acid, and the conformationally restricted diene (dienylcarbamate), which was realized by the introduction of a substituent at the 2-position of the diene unit, is the key to achieving the -DA reaction.

Computational molecular refinement to enhance enantioselectivity by reinforcing hydrogen bonding interactions in major reaction pathway.

Computational analyses have revealed that the distortion of a catalyst and the substrates and their interactions are key to determining the stability of the transition state. Hence, two strategies "distortion strategy" and "interaction strategy" can be proposed for improving enantiomeric excess in enantioselective reactions. The "distortion strategy" is used as a conventional approach that destabilizes the TS (transition state) of the minor pathway.