Chaozhong Li

Silver-Catalyzed Radical Aminofluorination of Unactivated Alkenes in Aqueous Media

We report herein a mild and catalytic intramolecular aminofluorination of unactivated alkenes. Thus, with the catalysis of AgNO3, the reactions of various N-arylpent-4-enamides with Selectfluor reagent in CH2Cl2/H2O led to the efficient synthesis of 5-fluoromethyl-substituted γ-lactams. A mechanism involving silver-catalyzed oxidative generation of amidyl radicals and silver-assisted fluorine atom transfer was proposed.

Silver-Catalyzed Radical Phosphonofluorination of Unactivated Alkenes

We report herein a mild and catalytic phosphonofluorination of unactivated alkenes. With catalysis by AgNO3, the condensation of various unactivated alkenes with diethyl phosphite and Selectfluor reagent in CH2Cl2/H2O/HOAc at 40 °C led to the efficient synthesis of β-fluorinated alkylphosphonates with good stereoselectivity and wide functional group compatibility. A mechanism involving silver-catalyzed oxidative generation of phosphonyl radicals and silver-assisted fluorine atom transfer is proposed.

Silver-Catalyzed Decarboxylative Chlorination of Aliphatic Carboxylic Acids

Decarboxylative halogenation of carboxylic acids, the Hunsdiecker reaction, is one of the fundamental functional group transformations in organic chemistry. As the initial method requires the preparations of strictly anhydrous silver carboxylates, several modifications have been developed to simplify the procedures. However, these methods suffer from the use of highly toxic reagents, harsh reaction conditions, or limited scope of application. In addition, none is catalytic for aliphatic carboxylic acids. In this Article, we report the first catalytic Hunsdiecker reaction of aliphatic carboxylic acids. Thus, with the catalysis of Ag(Phen)(2)OTf, the reactions of carboxylic acids with t-butyl hypochlorite afforded the corresponding chlorodecarboxylation products in high yields under mild conditions. This method is not only efficient and general, but also chemoselective. Moreover, it exhibits remarkable functional group compatibility, making it of more practical value in organic synthesis. The mechanism of single electron transfer followed by chlorine atom transfer is proposed for the catalytic chlorodecarboxylation.

Silver-Catalyzed Radical Fluorination of Alkylboronates in Aqueous Solution

We report herein an efficient and general method for the deboronofluorination of alkylboronates. Thus, with the catalysis of AgNO3, the reactions of various alkylboronic acids or their pinacol esters with Selectfluor reagent in acidic aqueous solution afforded the corresponding alkyl fluorides under mild conditions. A broad substrate scope and wide functional group compatibility were observed. A radical mechanism is proposed for this site-specific fluorination.

Transition-metal-free, room-temperature radical azidofluorination of unactivated alkenes in aqueous solution

We report herein the transition-metal-free azidofluorination of unactivated alkenes. Thus, the condensation of various alkenes with TMSN3 and Selectfluor in aqueous CH3CN at RT led to the efficient and regioselective synthesis of β-fluorinated alkyl azides with excellent functional group compatibility and good stereoselectivity. A single electron transfer mechanism involving the oxidative generation of azidyl radicals is proposed.

Silver-Catalyzed Decarboxylative Allylation of Aliphatic Carboxylic Acids in Aqueous Solution.

Direct decarboxylative radical allylation of aliphatic carboxylic acids is described. With K2S2O8 as the oxidant and AgNO3 as the catalyst, the reactions of aliphatic carboxylic acids with allyl sulfones in aqueous CH3CN solution gave the corresponding alkenes in satisfactory yields under mild conditions. This site-specific allylation method is applicable to all primary, secondary, and tertiary alkyl acids and exhibits wide functional group compatibility.

Palladium-Catalyzed Sequential Cyanation/N-Addition/N-Arylation in One-Pot: Efficient Synthesis of Luotonin A and Its Derivatives

With the catalysis of palladium, a number of 2-bromo-N-(2-iodobenzyl)benzamides underwent sequential cyanation/N-addition/N-arylation leading to the efficient construction of isoindolo[1,2-b]quinazolin-10(12H)-ones in a two-stage, one-pot manner. This method also allowed the convenient synthesis of luotonin A and its derivatives.

Preference of β-Lactam Formation in Cu(I)-Catalyzed Intramolecular Coupling of Amides with Vinyl Bromides

A general and highly efficient synthesis of 4-alkylidene-2-azetidinones was achieved by the Cu(I)-catalyzed intramolecular C-N coupling of amides with vinyl bromides. This 4-exo ring closure was found to be fundamentally preferred over other modes (5-exo, 6-exo, and 6-endo) of cyclization under copper catalysis. Tandem C-N bond formation was then successfully developed to allow the convenient generation of medium-sized lactams.

Formal fluorine atom transfer radical addition: silver-catalyzed carbofluorination of unactivated alkenes with ketones in aqueous solution

In this article, we report the first examples of carbofluorination of unactivated alkenes. Under catalysis by AgNO3, the reactions of unactivated alkenes with Selectfluor reagent and active methylene compounds such as acetoacetates or 1,3-dicarbonyls in CH2Cl2–H2O–HOAc solution afforded the corresponding three-component condensation products under mild conditions. Furthermore, with the promotion of NaOAc, the AgOAc-catalyzed carbofluorination of various unactivated alkenes with Selectfluor and acetone proceeded smoothly in aqueous solution at 50 °C. The carbofluorination was efficient and highly regioselective, and enjoyed a broad substrate scope and wide functional group compatibility. These formal fluorine atom transfer radical addition reactions provide a convenient entry to structurally divergent, polyfunctional organofluorine compounds as versatile synthetic intermediates.

Total Synthesis of (+)-Decursivine

The first asymmetric synthesis of natural indole alkaloid (+)-decursivine was accomplished. The key step involves the PIFA-mediated intramolecular [3 + 2] cycloaddition of 5-hydroxytryptophan with a substituted cinnamamide in a highly diastereoselective manner.