Iron catalyzed tandem ring opening/1,6-conjugate addition of cyclopropanols with p-quinone methides: new access to γ,γ-diaryl ketones

Iron-Catalyzed Oxidative Rearrangement of Cyclopropanone Hemiaminals: General Access to Pyrroloindolones from Indoles

A concise synthetic approach to medicinally relevant pyrroloindolones and related fused heterocycles is reported via the diastereoselective N-addition of unprotected indoles to readily accessible cyclopropanone equivalents. The resulting stable hemiaminals are shown to smoothly rearrange to pyrroloindolones in mild conditions using Fe(III) catalysis in the presence of inexpensive ammonium persulfate as a stoichiometric oxidant. Experimental evidence points toward the formation of a β-carboxylic radical intermediate prone to cyclization and oxidative rearomatization as the operative mechanistic pathway.

An Intermolecular Hydroarylation of Unactivated Arylcyclopropane via Re2O7/HFIP-Mediated Ring Opening

In this paper, we describe a Re2O7-mediated ring-opening arylation of unactivated arylcyclopropane because of its functionalization with various arenes via Friedel-Crafts-type reactivity. This protocol allows facile access to functionalized 1,1-diaryl alkanes and is characterized by a broad substrate scope, mild reaction conditions, high efficiency, and high atom economy. Both density functional theory calculations and deuterium labeling experiments were carried out to justify the indispensable role of HFIP in this transformation and pointed to Re2O7-mediated ring opening being the rate-determining step.

Site-selective ring opening of bicyclo[n.1.0]alkanols: an Fe(II)-catalyzed 1,6-conjugate addition to p-quinone methides

Herein, we report an efficient synthetic strategy for an Fe(ii)-catalyzed site-selective ring opening of bicyclo[n.1.0]alkanols and their concomitant 1,6-conjugate addition to p-quinone methides. Access to tertiary carbon centers with appendaged carbocycles of distinct sizes and functional groups are achieved, under a substrate-controlled bond scission of the fused cyclopropanols. Synthetic derivatizations further enhance the utility of the protocol.

Regiocontrol via Electronics: Insights into a Ru-Catalyzed, Cu-Mediated Site-Selective Alkylation of Isoquinolones via a C-C Bond Activation of Cyclopropanols

A site-selective C(3)/C(4)-alkylation of N-pyridylisoquinolones is achieved by employing C-C bond activation of cyclopropanols under Ru(II)-catalyzed/Cu(II)-mediated conditions. The regioisomeric ratios of the products follow directly from the electronic nature of the cyclopropanols and isoquinolones used, with electron-withdrawing groups yielding predominantly the C(3)-alkylated products, whereas the electron-donating groups primarily generate the C(4)-alkylated isomers. Density functional theory calculations and detailed mechanistic investigations suggest the simultaneous existence of the singlet and triplet pathways for the C(3)- and C(4)-product formation. Further transformations of the products evolve the utility of the methodology thereby yielding scaffolds of synthetic relevance.

BF3 ⋅Et2 O-Catalyzed Selective C-4 Alkylation of Isoquinolin-1(2H)-ones Employing p-Quinone Methides

The direct C-4 alkylation of isoquinolin-1(2H)-one moiety is a challenging transformation in organic synthesis. Here we present a practical and efficient synthesis of C-4 alkylated isoquinolin-1(2H)-ones through conjugate addition of isoquinolin-1(2H)-ones to p-quinone methides for the first time. The process is facilitated by Lewis acid catalysis and this operationally straightforward, mild, metal-free and one-pot transformation provides a wide range of C-4 alkylated isoquinolin-1(2H)-ones at ambient temperature in good to excellent yields.

Room-Temperature ZnBr2 -Catalyzed Regioselective 1,6-Hydroarylation of Electron-Rich Arenes to para-Quinone Methides: Synthesis of Unsymmetrical Triarylmethanes

A mild and efficient Zn(II)-catalyzed regioselective 1,6-hydroarylation of para-quinone methides (p-QMs) with electron-rich arenes protocol is reported. A variety of electron-rich arenes and para-quinone methides are well tolerated under mild conditions, delivering a broad range of triarylmethanes in good to excellent yields. The present method also works well for the hydroarylation of p-QMs with other nucleophiles, such as aniline, indole and phenol derivatives, offering the corresponding triarylmethanes with good yields under the standard conditions. The possible mechanism for the formation of C(sp³ )-C(sp² ) bonds in hydroarylation reactions has been explored by step-by-step control experiments, and the reaction may follow a second-order manner in a chemical kinetic study.

Preparation of Chitosan-Composite-Film-Supported Copper Nanoparticles and Their Application in 1,6-Hydroboration Reactions of p-Quinone Methides

Here, we describe the preparation of copper nanoparticles that are stabilized on a chitosan composite film (CP@Cu). This material could catalyze the 1,6-hydroboration reactions of p-quinone methides with B₂pin₂ as a boron source under mild conditions. This reaction exhibited very good functional group compatibility, and the organoboron compounds that were formed could easily be converted into corresponding hydroxyl products with good to excellent yields. This newly developed methodology provides an efficient and sequential pathway for the synthesis of gem-disubstituted methanols.