A novel tandem Pd-catalyzed intramolecular allylic decarboxylative coupling and “diradical conjugated 1,3-dien-5-yne cycloaromatization”: An unusual ortho -selectivity in the cycloaromatization and the mechanistic implications

Identifying reactive normal modes and their effect on regioselectivity in Myers-Saito and Schmittel cyclization of enyne-allenes: a combined perspective between the reaction force constant and statistical tools

This paper presents a theoretical study on the distinguishable regiodivergent C2-C7 Myers-Saito and C2-C6 Schmittel routes of benzannelated enyne-allene cycloaromatizations, in which substitutions on the terminal alkyne by alkyl (-CH3, -CH2CH3, -CH(CH3)2 and -C(CH3)3) and aryl (-C6H5 and -C6H2(CH3)3) groups were included. Mechanistic differences were found between substituents attached to alkynes with and without α-H, whereas in the former the Schmittel cyclization proceeds together with 1,8-H migration, in the latter it does so as the sole primitive event. It was also observed that bulky substituents preferentially favor the C2-C6 Schmittel route, and the statistical prediction of regioselectivity is greatly affected when the ratio of accessible vibrational microstates of the transition states is included, especially in highly competing routes, i.e., ΔΔG‡ → 0. Aiming to gain a deeper understanding, an analysis based on reaction force F(ξ) and reaction force constant κ(ξ) was performed to gain insights into the competing routes. The reactive normal modes were unveiled by means of the correlation between κ(ξ) and the force constant of reaction modes κi(ξ), given by a statistical protocol based on the partial least square with vector importance in projection (PLS-VIP) method. These findings suggest how the vibrational energy can be reorganized in competing paths from a static approach.

Cu-Catalyzed Tandem C-N and C-C Bond Formation Leading to 4(1H)-Quinolones: A Scaffold with Diverse Biological Properties from Totally New Raw Materials in a Single Step

A novel Cu-catalyzed tandem C-N and C-C bond-formation reaction has been developed to furnish 2-substituted-4-(1H)-quinolones. 4-(1H)-quinolones play an important role in medicinal chemistry. Many 2-aryl(alkyl)-4(1H)-quinolones are found to exhibit diverse biological properties. While traditional methods have inherent issues [like starting materials with incompatible functional groups (NH2 and keto groups)], many modern methods either require activated starting materials (like Ynones) or employ expensive metals (Pd, Rh, Au, etc.) involving carbonylation using CO or metal complexes. Our protocol presents an environmentally friendly one-step method for the construction of these useful 2-substituted-4-(1H)-quinolones from easily available aryl boronic acid (or pinacolate ester) and nitriles as new raw materials, using a cheap Cu-catalyst and O2 (air) as a green oxidant. We further extended its application to the synthesis of various natural products, including the first formal total synthesis of punarnavine. A plausible mechanism involving an aryl nitrilium ion (formed due to the intermolecular C-N bond-forming coupling between aryl boron species and the nitrile group) followed by tandem intramolecular C-C bond formation has been proposed.