The silver-catalyzed decarboxylative trifluoromethylation of aliphatic carboxylic acids is described. With AgNO3 as the catalyst and K2S2O8 as the oxidant, the reactions of aliphatic carboxylic acids with (bpy)Cu(CF3)3 (bpy = 2,2′-bipyridine) and ZnMe2 in aqueous acetonitrile at 40 °C afford the corresponding decarboxylative trifluoromethylation products in good yield. The protocol is applicable to various primary and secondary alkyl carboxylic acids and exhibits wide functional group compatibility. Mechanistic studies reveal the intermediacy of –Cu(CF3)3Me, which undergoes reductive elimination and subsequent oxidation to give Cu(CF3)2 as the active species responsible for the trifluoromethylation of alkyl radicals.

The copper-mediated trifluoromethylation of alkyl radicals is described. The combination of Et3SiH and K2S2O8 initiates the radical reactions of alkyl bromides or iodides with BPyCu(CF3)3 (BPy = 2,2′-bipyridine) in aqueous acetone at room temperature to afford the corresponding trifluoromethylation products in good yield. The protocol is applicable to various primary and secondary alkyl halides and exhibits wide functional group compatibility. A mechanism involving trifluoromethyl group transfer from Cu(II)–CF3 intermediates to alkyl radicals is proposed.

The silver-catalyzed Hunsdiecker bromination of aliphatic carboxylic acids is described. With Ag(Phen)2OTf as the catalyst and dibromoisocyanuric acid as the brominating agent, various aliphatic carboxylic acids underwent decarboxylative bromination to provide the corresponding alkyl bromides under mild conditions. This method not only is efficient and general but also enjoys wide functional group compatibility. An oxidative radical mechanism involving Ag(II) intermediates is proposed.

The trifluoromethylalkynylation of unactivated alkenes with alkynyl sulfones and Togni’s reagent was developed. The reaction was catalyzed by 2,4,6-trimethylpyridine, leading to various β-trifluoromethylated alkynes under metal-free conditions with a broad substrate scope and wide functional group compatibility. A mechanism involving catalytic nonchain radical processes is proposed.

AbstractThe first total synthesis of the hexacyclic indole alkaloid (±)-corymine is described. Starting from the readily available N-protected tryptamine, the title compound was achieved in 21 steps in 3.4 % overall yield. Key steps of the synthesis include: a) the addition of a malonate to a 3-bromooxindole to afford 3,3-disubstituted oxindole, b) the formation of a 12-membered cyclic enol ether by intramolecular O-propargylation, immediately followed by propargyl Claisen rearrangement to provide the α-allenyl ketone stereospecifically, c) DMDO oxidation to install a hydroxy group in a highly stereoselective manner, and d) the SmI2-mediated reductive C−O bond cleavage to remove the α-keto carboxyl group.

The AgNO3-catalyzed reactions of unactivated alkenes with acetic acid and Selectfluor reagent in aqueous solution afforded the corresponding γ-fluorinated carboxylic acids under mild conditions. Carbofluorination was not only efficient and regioselective, but also enjoyed a wide functional group compatibility.

AbstractDirect fluorination of tertiary alkyl bromides and iodides with Selectfluor is described. The halogen-exchange fluorination proceeds efficiently in acetonitrile at room temperature under metal-free conditions and exhibits a wide range of functional group compatibility. Furthermore, the reactions are highly selective in that alkyl chlorides and primary and secondary alkyl bromides remain intact. A radical mechanism is proposed for this selective fluorination.

AbstractDirect fluorination of tertiary alkyl bromides and iodides with Selectfluor is described. The halogen-exchange fluorination proceeds efficiently in acetonitrile at room temperature under metal-free conditions and exhibits a wide range of functional group compatibility. Furthermore, the reactions are highly selective in that alkyl chlorides and primary and secondary alkyl bromides remain intact. A radical mechanism is proposed for this selective fluorination.

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.

The stereoselectivity in the 6-exo cyclization of α-carbamoyl radicals was investigated experimentally and theoretically. The BEt3/O2-initiated iodine-atom-transfer radical cyclization reactions of substituted N-(but-3-en-1-yl)-N-(tert-butyl)-2-iodoalkanamides were carried out, which led to the predominant formations of 3,4-cis, 4,5-trans, or 4,6-trans substituted δ-lactams. Density functional calculations at the B3LYP/6-31G* level revealed that the 6-exo radical cyclization proceeds via boat-conformational transition states. Furthermore, a mechanistic insight into the stereoselectivity was provided and the calculation results were in excellent agreement with the experimental observations.

We report herein an efficient and general method for the decarboxylative azidation of aliphatic carboxylic acids. Thus, with AgNO3 as the catalyst and K2S2O8 as the oxidant, the reactions of various aliphatic carboxylic acids with tosyl azide or pyridine-3-sulfonyl azide in aqueous CH3CN solution afforded the corresponding alkyl azides under mild conditions. A broad substrate scope and wide functional group compatibility were observed. A radical mechanism is proposed for this site-specific azidation.

With the catalysis of CuI/3,4,7,8-tetramethyl-1,10-phenanthroline, various ketones smoothly underwent the intramolecular C-vinylation with vinyl bromides in refluxing THF leading to the efficient synthesis of the corresponding multisubstituted cyclobutenones.

We report herein a facile synthesis of α-methylene-β-lactams. Thus, under the catalysis of triphenylphosphine, a number of 2-propiolamidoacetates or α-propiolamido ketones in refluxing ethanol underwent umpolung cyclization to afford the corresponding 4-substituted 3-methyleneazetidin-2-ones in high yields.

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.

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.

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.

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)2OTf, 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.

Although fluorinated compounds have found widespread applications in the chemical and materials industries, general and site-specific C(sp3)–F bond formations are still a challenging task. We report here that with the catalysis of AgNO3, various aliphatic carboxylic acids undergo efficient decarboxylative fluorination with SELECTFLUOR® reagent in aqueous solution, leading to the synthesis of the corresponding alkyl fluorides in satisfactory yields under mild conditions. This radical fluorination method is not only efficient and general but also chemoselective and functional-group-compatible, thus making it highly practical in the synthesis of fluorinated molecules. A mechanism involvinig Ag(III)-mediated single electron transfer followed by fluorine atom transfer is proposed for this catalytic fluorodecarboxylation.

With the promotion of Lewis acid BF3•OEt2, various N-(hex-5-enyl)-2-iodoalkanamides underwent efficient and regioselective 9-endo iodine-atom-transfer radical cyclization reactions at room temperature. The cyclized products were readily converted to the corresponding azonan-2-ones by reduction with Bu3SnH or to hexahydroindolizin-3(5H)-ones by treatment with aqueous Na2CO3 in a one-pot, two-stage manner.

Unsaturated primary amidyl radicals of Z-configurations underwent efficient chemo- and stereoselective 6-exo cyclization reactions via chair-conformational transition states, leading to the predominant formations of 3,6-trans, 4,6-cis, or 5,6-trans substituted δ-lactams.

The iodine-atom-transfer 8-endo cyclization of α-carbamoyl radicals was investigated experimentally and theoretically. With the aid of Mg(ClO4)2 and a bis(oxazoline) ligand, N-ethoxycarbonyl-substituted N-(pent-4-enyl)-2-iodoalkanamides underwent 8-endo cyclization leading to the formation of only the corresponding 3,5-trans-substituted azocan-2-ones in excellent yields. Similarly, the BF3·OEt2/H2O-promoted reactions of N-ethoxycarbonyl-N-(2-allylaryl)-2-iodoalkanamides afforded exclusively the benzazocanone products with a 3,5-cis configuration in high yields. The bidentate chelation of substrate radicals not only significantly improved the efficiency of cyclization but also resulted in the change of stereochemistry of azocanone products from 3,8-trans to 3,8-cis. Theoretical calculations at the UB3LYP/6-31G* level revealed that the cyclization of N-carbonyl-substituted α-carbamoyl radicals occurs via the E-conformational transition states without the presence of a Lewis acid. On the other hand, the cyclization proceeds via the Z-conformational transition states when the substrates form the bidentate chelation with a Lewis acid. In both cases, the 8-endo cyclization is always fundamentally preferred over the corresponding 7-exo cyclization. The complexed radicals having the more rigid conformations also allow the better stereochemical control in the iodine-atom-abstraction step. To further understand the reactivity of α-carbamoyl radicals, the competition between the 8-endo and 5-exo cyclization was also studied. The results demonstrated that the 8-endo cyclization is of comparable rate to the corresponding 5-exo cyclization for α-carbamoyl radicals with fixed Z-conformational transition states. As a comparison, the 8-endo mode is fundamentally preferred over the 5-exo mode in the cyclization of NH-amide substrates because the latter requires the Z-conformational transition states, whereas the former proceeds via the more stable E-conformational transition states.

The first asymmetric synthesis of indole alkaloid (+)-subincanadine F was successfully accomplished with the uncommon 7-endo-trig stereoselective radical cyclization as the key step and its absolute configuration was thus assigned.

With the catalysis of CuI/3,4,7,8-tetramethyl-1,10-phenanthroline, various ketones smoothly underwent the intramolecular O-vinylation with vinyl bromides leading to the efficient synthesis of the corresponding multisubstituted furans.

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.

With the catalysis of CuI/trans-N,N′-dimethylcyclohexane-1,2-diamine, a number of carboxylic acids underwent efficient intramolecular O-vinylation with vinyl bromides leading to the synthesis of the corresponding five- and six-membered enol lactones. The same catalytic system also led to the efficient cycloisomerization of alkynoic acids.

With chemoselective Dieckmann condensation as the key step, the protective-group-free total synthesis of (±)-subincanadine F was accomplished in 7 steps from the commercially available tryptamine in 33% overall yield.

The first copper-catalyzed intramolecular O-vinylation of carbonyl compounds with vinyl bromides was reported, among which the efficient formation of 5-, 6- and even 7-membered cyclic alkenyl ethers was achieved with β-ketoesters as nucleophiles.

C(sp3)–C(sp) bond formations are of immense interest in chemistry and material sciences. We report herein a convenient, radical-mediated and catalytic method for C(sp3)–C(sp) cross-coupling. Thus, with AgNO3 as the catalyst and K2S2O8 as the oxidant, various aliphatic carboxylic acids underwent decarboxylative alkynylation with commercially available ethynylbenziodoxolones in aqueous solution under mild conditions. This site-specific alkynylation is not only general and efficient but also functional group compatible. In addition, it exhibits remarkable chemo- and stereoselectivity.

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.

The AgNO3-catalyzed reactions of unactivated alkenes with acetic acid and Selectfluor reagent in aqueous solution afforded the corresponding γ-fluorinated carboxylic acids under mild conditions. Carbofluorination was not only efficient and regioselective, but also enjoyed a wide functional group compatibility.

The highly efficient and stereocontrolled dimerization of 1,2,3,8-tetrahydropyrrolo[2,3-b]indoles was successfully developed with I2 as the oxidant, which allowed the rapid synthesis of meso- and rac-chimonanthines, (+)-WIN 64821 and (+)-WIN 64745 in the highest overall yields to date via the oxidation–oxidation–reduction sequence.

The first asymmetric synthesis of indole alkaloid (+)-subincanadine F was successfully accomplished with the uncommon 7-endo-trig stereoselective radical cyclization as the key step and its absolute configuration was thus assigned.

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.