Metal-free oxidative cross-dehydrogenative coupling of quinones with benzylic C(sp3)–H bonds

Blue-Light Irradiated Mn(0)-Catalyzed Hydroxylation and C(sp3 )-H Functionalization of Unactivated Alkanes with C(sp2 )-H Bonds of Quinones for Alkylated Hydroxy Quinones and Parvaquone

Site-selective C(sp3 )-H functionalization of unreactive hydrocarbons is always challenging due to its inherited chemical inertness, slightly different reactivity of various C-H bonds, and intrinsically high bond dissociation energies. Here, a site-selective C-H alkylation of naphthoquinone with unactivated hydrocarbons using Mn2 (CO)10 as a catalyst under blue-light (457 nm) irradiation without any external acid or base and pre-functionalization is presented. The selective C-H functionalization of tertiary over secondary and secondary over primary C(sp3 )-H bonds in abundant chemical feedstocks was achieved, and hydroxylation of quinones was realized in situ by employing the developed methodology. This protocol provides a new catalytic system for the direct construction of high-value-added compounds, namely, parvaquone (a commercially available drug used to treat theileriosis) and its derivatives under ambient reaction conditions. Moreover, this operationally simple protocol applies to various linear-, branched-, and cyclo-alkanes with high degrees of site selectivity under blue-light irradiated conditions and could provide rapid and straightforward access to versatile methodologies for upgrading feedstock chemicals. Mechanistic insight by radical trapping, radical scavenging, EPR, and other controlled experiments well corroborated with DFT studies suggest that the reaction proceeds by a radical pathway.

Copper(I)-Mediated Divergent Synthesis of Pyrroquinone Derivatives and 2-Halo-3-amino-1,4-quinones

A divergent transformation of 2-amino-1,4-quinones for the synthesis of pyrroquinone derivatives and 2-halo-3-amino-1,4-quinones was disclosed. The mechanistic study showed that both the tandem cyclization and halogenation involved a Cu(I)-catalyzed oxidative radical process. This protocol not only constructed a series of novel pyrroquinone derivatives with high atom economy but also provided a new method of halogenation via directed C(sp²)-H functionalization with CuX (X = I, Br, Cl) serving as the X (X = I, Br, Cl) source.

Bioinspired Photoredox Benzylation of Quinones

3-Benzylmenadiones were obtained in good yield by using a blue-light-induced photoredox process in the presence of Fe(III), oxygen, and γ-terpinene acting as a hydrogen-atom transfer agent. This methodology is compatible with a wide variety of diversely substituted 1,4-naphthoquinones as well as various cheap, readily available benzyl bromides with excellent functional group tolerance. The benzylation mechanism was investigated and supports a three-step radical cascade with the key involvement of the photogenerated superoxide anion radical.

Copper-catalyzed one-pot amine-alkylation of quinones with amines and alkanes

A copper-catalyzed one-pot amine-alkylation of quinones with amines and alkanes in the presence of di-tert-butyl peroxide (DTBP) was developed via a radical reaction process. Various alkanes and aromatic or aliphatic amines with diverse structures and electronic properties are suitable substrates, and the chirality of amines can be maintained for the transformation. This method has high step and atom economy for straightforward access to aminated and alkylated quinones from readily available starting materials.

B(C6F5)3-catalyzed three-component tandem reaction to construct novel polycyclic quinone derivatives: synthesis of a carbonate salt chromogenic chemosensor

A series novel polycyclic quinone derivatives were constructed providing a carbonate salt chromogenic chemosensor.