Huijin Feng

Rhodium‐Catalyzed Directed Sulfenylation of Arene CH Bonds

The rhodium-catalyzed intermolecular direct C-H thiolation of arenes with aryl and alkyl disulfides was developed for the first time to provide a convenient route to aryl thioethers. This strategy is compatible with many different directing groups and exhibits excellent functional group tolerance. More significantly, mono- or dithiolation can be selectively achieved, thus providing a straightforward way for selective preparation of aryl thioethers and dithioethers.

Rhodium‐Catalyzed Synthesis of Amides from Aldehydes and Azides by Chelation‐Assisted CH Bond Activation

Rhodium-Catalyzed Synthesis of Amides from Aldehydes and Azides by Chelation-Assisted C H Bond Activation C H activation : A Rh-catalyzed direct aldehyde C H amidation has been achieved with sulfonyl, aryl, and alkyl azides as the amine sources, and release of N2 as the only byproduct (see scheme). More importantly, this catalytic reaction proceeds in the absence of external oxidants or additives, under mild conditions, at neutral pH under air. This reaction represents a new avenue for practical intermolecular C N bond formation by aldehyde C H bond activation. Cp*= 1,2,3,4,5Pentamethylcyclopentadiene

Rh(III)-catalyzed addition of alkenyl C-H bond to isocyanates and intramolecular cyclization: direct synthesis 5-ylidenepyrrol-2(5H)-ones.

The rhodium-catalyzed addition of an alkenyl C-H bond to isocyanates via sp(2) C-H bond activation followed by an intramolecular cyclization is described. This atom-economic and catalytic reaction affords a simple and straightforward access to biologically relevant 5-ylidene pyrrol-2(5H)-ones and can be carried out under mild and neutral conditions in the absence of any additives and environmentally hazardous waste production.

Rh(III)-Catalyzed Intramolecular Redox-Neutral or Oxidative Cyclization of Alkynes: Short, Efficient Synthesis of 3,4-Fused Indole Skeletons

A Rh(III)-catalyzed intramolecular redox-neutral or oxidative annulation of a tethered alkyne has been developed to efficiently construct 3,4-fused indoles via a C-H activation pathway. The advantages of this process are (1) ready availability of annulation precursors; (2) broad substrate scope; (3) complete regioselectivity; (4) simple and mild reaction conditions; and (5) no need for an external oxidant or to employ molecular oxygen as the stoichiometric terminal oxidant.

Rh(III)-catalyzed C-H amidation with N-hydroxycarbamates: a new entry to N-carbamate-protected arylamines.

An unprecedented Rh(III)-catalyzed direct intermolecular C-H amidation with N-hydroxycarbamates has been developed. Different directing groups, such as pyridine, pyrimidine, pyrazole, and N-OMe oxime, can be employed in this C-H amidation process, providing valuable N-carbamate-protected arylamines (e.g., Cbz, Moz, Ac, Boc, and Fmoc). More importantly, this process may afford a new avenue for intermolecular C-H amidation where readily available N-hydroxycarbamates can be used as the nitrogen source.

Copper(I)-Catalyzed Aryl or Vinyl Addition to Electron-Deficient Alkenes Cascaded by Cationic Cyclization

An exoselective copper-catalyzed arylation- and vinylation-carbocyclization of electron-deficient alkenes was developed to provide rapid and efficient access to a variety of functionalized 3,3-disubstituted oxindoles. With this method, a highly efficient and concise formal synthesis of (±)-physostigmine and (±)-physovenine has been completed.

Rhodium-Catalyzed Direct Addition of Aryl C–H Bonds to Nitrosobenzenes at Room Temperature

An unprecedented Rh-catalyzed direct addition of aryl C-H bonds to nitrosobenzenes has been developed under very mild reaction conditions (room temperature). The reaction is highly step-, atom-, and redox-economic and compatible with air and water to N-selectively provide a variety of N-diarylhydroxylamines in good to excellent yields. More importantly, this process may provide a new direction for C-N bond formation through direct C(sp(2))-H functionalization.

Access to Six- and Seven-Membered 1,7-Fused Indolines via Rh(III)-Catalyzed Redox-Neutral C7-Selective C-H Functionalization of Indolines with Alkynes and Alkenes.

We report herein a new strategy for the Rh(III)-catalyzed redox-neutral C7-selective C-H activation/annulation of indolines to rapidly access various privileged 1,7-fused indolines by utilizing an oxidizing-directing group. For example, a Rh(III)-catalyzed redox-neutral C7-selective C-H functionalization of indolines with arylalkynes is described to directly access 7-membered 1,7-fused indolines. Moreover, an unprecedented intramolecular addition of an alkenyl-Cp*Rh(III) species to a carbamoyl moiety occurred to give 1H-pyrroloquinolinones when employing alkyl alkynes. Additionally, an efficient Rh(III)-catalyzed redox-neutral C7-selective C-H activation/alkenylation/aza-Michael addition of indolines is also developed to give 6-membered 1,7-fused indolines. The advantages of these processes are as follows: (1) mild and simple reaction conditions; (2) no need for an external oxidant; (3) broad scope of substrates; and (4) valuable six- or seven-membered 1,7-fused indolines as products.

Rhodium-Catalyzed Direct Amination of Arenes with Nitrosobenzenes: A New Route to Diarylamines

A Rh(III) -catalyzed addition of aryl CH bonds to nitrosobenzenes, followed by cleavage of the resulting hydroxylamines in situ, has been reported. Different directing groups, such as N-based heterocycles and ketoximes, can be used in this CH amination process, providing valuable diarylamines in excellent yields. Most importantly, this process provides a new method for attaching arylamine groups to aromatic rings.

Design and Synthesis of Novel C14-Hydroxyl Substituted Triptolide Derivatives as Potential Selective Antitumor Agents

It has long been considered that the free beta hydroxyl group at C14 of triptolide (1) is essential to its potent anticancer activity. In this study, we synthesized novel derivatives of 1 with a hydroxyl group substituted by epoxy groups (4-8) or a five-membered ring (11-13). Compounds (4-8) showed significant in vitro anticancer activity although less potent than 1. Although with an alpha oxygen configuration at the C14 position, (14S)-14,21-epoxytriptolide (4) exhibited the highest potency among all these derivatives, clearly challenging the traditional viewpoint on the necessity of C14beta-hydroxyl group of compound 1. Further studies revealed that while displaying broad spectrum in vitro anticancer activity, compound 4 demonstrated prominent selective in vivo anticancer activity, particularly against human ovarian SK-OV-3 and prostate PC-3 cancers with obviously lower toxicity than 1. Noticeably, compound 4 was also highly effective against multidrug resistant cancer cells. Therefore, our study gives new insights into the structure-activity relationship of 1 and also produces a promising anticancer drug candidate with unique anticancer activities.