Xinyao Li

Mn-Catalyzed Highly Efficient Aerobic Oxidative Hydroxyazidation of Olefins: A Direct Approach to β-Azido Alcohols

An efficient Mn-catalyzed aerobic oxidative hydroxyazidation of olefins for synthesis of β-azido alcohols has been developed. The aerobic oxidative generation of azido radical employing air as the terminal oxidant is disclosed as the key process for this transformation. The reaction is appreciated by its broad substrate scope, inexpensive Mn-catalyst, high efficiency, easy operation under air, and mild conditions at room temperature. This chemistry provides a novel approach to high value-added β-azido alcohols, which are useful precursors of aziridines, β-amino alcohols, and other important N- and O-containing heterocyclic compounds. This chemistry also provides an unexpected approach to azido substituted cyclic peroxy alcohol esters. A DFT calculation indicates that Mn catalyst plays key dual roles as an efficient catalyst for the generation of azido radical and a stabilizer for peroxyl radical intermediate. Further calculation reasonably explains the proposed mechanism for the control of C-C bond cleavage or for the formation of β-azido alcohols.

From Ketones to Esters by a Cu-Catalyzed Highly Selective C(CO)–C(alkyl) Bond Cleavage: Aerobic Oxidation and Oxygenation with Air

The Cu-catalyzed aerobic oxidative esterification of simple ketones via C-C bond cleavage has been developed. Varieties of common ketones, even inactive aryl long-chain alkyl ketones, are selectively converted into esters. The reaction tolerates a wide range of alcohols, including primary and secondary alcohols, chiral alcohols with retention of the configuration, electron-deficient phenols, as well as various natural alcohols. The usage of inexpensive copper catalyst, broad substrate scope, and neutral and open air conditions make this protocol very practical. (18)O labeling experiments reveal that oxygenation occurs during this transformation. Preliminary mechanism studies indicate that two novel pathways are mainly involved in this process.

Rh-Catalyzed Construction of Quinolin-2(1H)-ones via C-H Bond Activation of Simple Anilines with CO and Alkynes.

A novel and efficient Rh-catalyzed carbonylation and annulation of simple anilines with CO and alkynes through N-H and C-H bond activation for the direct synthesis of quinolin-2(1H)-ones has been developed. Simple anilines without preactivation, broad substrate scope with hetero/polycycles, and high-value products make this protocol very practical and attractive. A key rhodacycle complex was isolated and well-characterized.

I2- or NBS-Catalyzed Highly Efficient α-Hydroxylation of Ketones with Dimethyl Sulfoxide

An efficient method for the direct preparation of high synthetic valuable α-hydroxycarbonyls is described. The simple and readily available I2 or NBS was used as catalyst. DMSO acts as the oxidant, oxygen source, and solvent. A diverse range of tertiary Csp(3)-H bonds as well as more challenging secondary Csp(3)-H bonds could be hydroxylated in this transformation. The reaction is mild, less toxic and easy to perform.

Dehydrogenative N‐Incorporation: A Direct Approach to Quinoxaline N‐Oxides under Mild Conditions

An efficient method for the synthesis of quinoxaline N-oxides proceeds by the dehydrogenative N-incorporation of simple imines by C(sp(2))-H and C(sp(3))-H bond functionalization. The overall transformation involves the cleavage of three C-H bonds. The reaction is easily handled and proceeds under mild conditions. Simple and readily available tert-butyl nitrite (TBN) was employed as the NO source.

Silver-Catalyzed Decarboxylative Azidation of Aliphatic Carboxylic Acids

The catalytic decarboxylative nitrogenation of aliphatic carboxylic acids for the synthesis of alkyl azides is reported. A series of tertiary, secondary, and primary organoazides were prepared from easily available aliphatic carboxylic acids by using K2S2O8 as the oxidant and PhSO2N3 as the nitrogen source. The EPR experiment sufficiently proved that an alkyl radical process was generated in the process, and DFT calculations further supported the SET process followed by a stepwise SH2 reaction to afford azide product.

Ceric ammonium nitrate (CAN) catalyzed modification of ketones via two C-C bond cleavages with the retention of the oxo-group.

A simple ceric ammonium nitrate (CAN) catalyzed functionalization of ketones through double C-C bond cleavage strategy has been disclosed. This reaction provides a mild, practical method toward carbamoyl azides, which are versatile intermediates and building blocks in organic synthesis. Based on relevant mechanistic studies, a unique and plausible C-C bond and N-O bond cleavage process is proposed, where the oxyamination intermediate plays an important role in this reaction.

Conversion of Simple Cyclohexanones into Catechols

A novel I2-catalyzed direct conversion of cyclohexanones to substituted catechols under mild and simple conditions has been described. This novel transformation is remarkable with the multiple oxygenation and dehydrogenative aromatization processes enabled just by using DMSO as the solvent, oxidant, and oxygen source. This metal-free and simple system demonstrates a versatile protocol for the synthesis of highly valuable substituted catechols and therefore streamlines the synthesis and modification of biologically important molecules for drug discovery.

Fe-Catalyzed Amination of (Hetero)Arenes with a Redox-Active Aminating Reagent under Mild Conditions

A novel and efficient Fe-catalyzed direct C-H amination (NH2 ) of arenes is reported using a new redox-active aminating reagent. The reaction is simple, and can be performed under air, mild, and redox-neutral conditions. This protocol has a broad substrate scope and could be used in the late-stage modification of bioactive compounds. Mechanistic studies demonstrate that a radical pathway could be involved in this transformation.

Copper-Catalyzed Oxygenation Approach to Oxazoles from Amines, Alkynes, and Molecular Oxygen

A novel and efficient oxygenation approach to trisubstituted oxazoles via a copper-catalyzed aerobic oxidative dehydrogenative annulation of amines, alkynes, and O2 has been developed. This transformation combines dioxygen activation and oxidative C-H bond functionalization and provides a practical protocol for the preparation of oxazole derivatives, which are privileged units found in various bioactive compounds or other natural products. 18O-labeling experiments were conducted to reveal that oxygenation was involved in this chemistry.