Microwave-Assisted Copper Catalysis of α-Difluorinated gem-Diol toward Difluoroalkyl Radical for Hydrodifluoroalkylation of para-Quinone Methides

Copper-Catalyzed Difluoroalkylation Reaction

This review describes recent advances in copper-catalyzed difluoroalkylation reactions. The RCF₂ radical is generally proposed in the mechanism of these reactions. At present, various types of copper-catalyzed difluoroalkylation reactions have been realized. According to their characteristics, we classify these difluoroalkylation reactions into three types.

Metal-Free Reductive Coupling of para-Quinone Methides with 4-Cyanopyridines Enabled by Pyridine-Boryl Radicals: Access to Pyridylated Diarylmethanes with Anti-Cancer Activity

Reported herein is a streamlined protocol to produce pyridylated diarylmethanes through pyridine-boryl radical induced reductive coupling between para-quinone methides (p-QMs) and 4-cyanopyridines using bis(pinacolato)diboron (B₂ pin₂ ) as a templated reagent. The metal-free process is characterized by an operationally simple approach, excellent chemoselectivity (1,2- vs. 1,6-selectivity), and a broad substrate scope with good functional group compatibility. The mechanistic studies provided important insights into the reductive cross-coupling process between diarylmethyl radical and pyridine-boryl radical. Moreover, part of the obtained pyridylated diarylmethane products were screened against a panel of cancer cell lines, and 3 v was confirmed to significantly inhibit the proliferation of head and neck squamous cell carcinoma (HNSCC) cells. This method offers a platform for the preparation of new lead compounds with antitumor activity.

Divergent Synthesis of gem-Difluorinated Oxa-Spirocyclohexadienones by One-Pot Sequential Reactions of p-Hydroxybenzyl Alcohols with Difluoroenoxysilanes

A new efficient formal [2 + 3] cyclization of p-hydroxybenzyl alcohols with difluoroenoxysilanes has been established. This convenient one-pot sequential procedure enables the divergent construction of highly functionalized gem-difluorinated oxa-spirocyclohexadienones under mild conditions. As opposed to the common C1 synthons in previous studies, difluoroenoxysilanes acted as new 3-atom (CCO) synthons for the first time here. The AcOH and H₂O generated in the reaction are critical for the reactions to proceed smoothly.

Selective sulfonylation and isonitrilation of para-quinone methides employing TosMIC as a source of sulfonyl group or isonitrile group

Chemoselective sulfonylation and isonitrilation reactions for the divergent synthesis of valuable diarylmethyl sulfones and isonitrile diarylmethanes starting from easy-to-synthesize para-quinone methides (p-QMs) and commercially abundant p-toluenesulfonylmethyl isocyanide (TosMIC) by using respectively zinc iodide and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as catalysts were developed. The distinguishing feature of this method is that TosMIC plays a dual role from the same substrates in the reaction: as a sulfonyl source or as an isonitrile source. The synthetic utility of this protocol was also demonstrated in the synthesis of difluoroalkylated diarylmethane 5 and diarylmethane ketone derivatives 6 and 7, which are important core structures in natural products and medicines.

Iron-Catalyzed Ring Opening of Cyclopropanols and Their 1,6-Conjugate Addition to p-Quinone Methides

A novel iron-catalyzed ring opening of cyclopropanols and their 1,6-conjugate addition to p-quinone methides for accessing substituted phenols is disclosed. In this protocol, various cyclopropanols are converted to alkyl radicals and undergo 1,6-conjugate addition to p-quinone methides toward C-C bond formation. The salient features of this methodology include operationally simple and mild reaction conditions, environmentally benign protocol, high efficiency, inexpensive catalyst, good to excellent yield, and a wide range of substrate scope.