Visible-Light-Induced,Graphene Oxide-Promoted C3-Chalcogenylation of Indoles Strategy under Transition-Metal-Free Conditions

An efficient and general method for the synthesis of 3-sulfenylindoles and 3-selenylindoles employing visible-light irradiation with graphene oxide as a promoter at room temperature has been achieved. The reaction features are high yields, simple operation, metal-free and iodine-free conditions, an easy-to-handle oxidant, and gram-scalable synthesis. This simple protocol allows one to access a wide range of 3-arylthioindoles, 3-arylselenylindoles, and even 3-thiocyanatoindoles with good to excellent yields.     

Synthesis of tri-substituted biaryl based trianglimines: formation of C3-symmetrical and non-symmetrical regioisomers

2-Functionalised aromatic monoaldehydes were synthesised in good to excellent yields by reacting 4-bromo-2-fluorobenzaldehyde with different secondary amines and phenol. The Suzuki-coupling reaction of the newly functionalised aromatic monoaldehydes with 4-formylphenylboronic acid afforded the corresponding 2-functionalised-4,4'-biphenyldialdehydes in good yields (47-85%). The [3+3]-cyclocondensation reactions of the 2-functionalised-4,4'-biphenyldialdehydes with (1R,2R)-1,2-diaminocyclohexane afforded a mixture of regioisomeric C(3)-symmetrical and non-symmetrical trianglimines. Reduction of the C(3)-symmetrical and the non-symmetrical trianglimines with NaBH(4) in a mixture of THF and MeOH afforded the corresponding trianglamines in high yields.     

A general and efficient synthesis of sulfonylbenzotriazoles from N-chlorobenzotriazole and sulfinic acid salts

One-pot reactions of sulfinic acid salts (produced from organometallic reagents with SO2) with N-chlorobenzotriazole gave the corresponding N-alkane-, N-arene-, and N-heteroenesulfonylbenzotriazoles 3a-j in 41-93% yields. Reagents 3a-j are efficient sulfonylating agents, reacting at 20-80 degrees C with various primary and secondary aliphatic amines to yield the corresponding sulfonamides in 64-100% yields.     

A new and efficient method for conjugate addition of trialkylphosphites to 3-acylsubstituted coumarins

A new and efficient conjugate addition of trialkylphosphites to 3-ω-bromoacetylcoumarin 1 catalysed by p-toluenesulfonic acid (TsOH) has been studied. Under the same conditions, an enolphosphate gave the corresponding esters of 3-acetyl-4-phosphono-2-oxochromans in high yields. The use of TsOH in the reaction of 3-acetyl-, 3-benzoyl-, and 3-ethoxycarbonyl coumarins led mainly to 1,4-addition products—the corresponding 3-acyl-4-dialkylphosphono-2-oxochromans—in very good yields.     

Zinc-mediated chain extension reaction of 1,3-diketones to 1,4-diketones and diastereoselective synthesis of trans-1,2-disubstituted cyclopropanols

[reaction: see text] A variety of 1,3-diketones can be efficiently converted into the corresponding 1,4-diketones and trans-1,2-disubstituted cyclopropanols by using organozinc species in one-pot reactions. It was found that 2.3 equiv of CF3CO2ZnCH2I was effective to give the corresponding chain-extended products in 44-85% yields, while a mixture of organozinc species formed from 4.0 equiv of Et2Zn, 2.0 equiv of CF3CO2H, and 4.0 equiv of CH2I2 resulted in the formation of trans-1,2-disubstituted cyclopropanols with quite good yields and diastereoselectivity.     

Synthesis of carbazoles via an intramolecular cyclization of 2-(6-substituted 3(Z)-hexen-1,5-diynyl)anilines and their related molecules

Various 2-(6-substituted 3(Z)-hexen-1,5-diynyl)anilines 1a-g were treated with potassium tert-butoxide or potassium 3-ethylpentanoxide in NMP at 60 degrees C for 2 h to give the corresponding 5-substituted carbazoles 2a-g in 36-65% yields together with indoles 9a-g in 21-40% yields, respectively. Exposing the trifluoroacetamide analogues 10h-k under the same reaction conditions gave the carbazoles 2b-e in 37-57% yields and indoles 9b-e in 15-27% yields. Subsequent cyclizations of acetamide analogues 10a-g gave carbazoles 2a-g in 53-86% yields.     

Synthesis and reaction of selenocarbamic acid sodium and potassium salts and organo-germanium, -tin,and -lead esters

Sodium 2 and potassium selenocarbamates 3 were found to be synthesized in moderate to good yields by the reaction of carbamoyl chlorides with sodium and potassium selenides. The salts 2 and 3 reacted with alkyl halides and organo-germanium, -tin, and -lead chlorides to give the corresponding esters 7–9 in good yields.     

Reaction of 2-dimethylaminomethylene-1,3-diones with dinucleophiles. VIII. Synthesis of ethyl and methyl 2,4-disubstituted 5-pyrimidinecarboxylates

Reaction of ethyl or methyl 2-dimethylaminomethylene-3-oxoalkanoates with N-C-N dinucleophiles such as guanidine, acetamidine or benzamidine afforded in high yields the relative esters of 4-substituted 2-amino-, 2-methyl- or 2-phenyl-5-pyrimidinecarboxylic acids, respectively. These esters were hydrolyzed to the corresponding carboxylic acids, which were converted by heating to 4-substituted 2-pyrimidinamines, 2-methyl or 2-phenylpyrimidines, respectively, generally in excellent yields. The 4-unsubstituted ethyl 2-amino-, 2-methyl- and 2-phenyl-5-pyrimidinecarboxylates were obtained in moderate yields by reaction of the above dinucleophiles with ethyl 2,2-diformylacetate. These esters were hydrolyzed and the corresponding acids (with the exception of the 2-methyl derivative) were decarboxylated to give 2-pyrimidinamine and 2-phenylpyrimidine in satisfactory yields.     

A simple procedure for synthesis of 3H-quinazolin-4-one hydrazones under mild conditions

Condensation of 6-bromo- and 6,8-dibromo-2-hydrazino-3-phenyl-3H-quinazolin-4-ones with d-sugars in the presence of a catalytic quantity of glacial acetic acid gave the corresponding hydrazones in good yields. Acetylation of hydrazones with acetic anhydride in anhydrous pyridine gave the corresponding acetyl hydrazones in high yields. Also, other hydrazones were synthesized from condensation of 2-hydrazino-3H-quinazolin-4-ones with aromatic aldehydes in the presence of a catalytic quantity of piperidine.     

Indium-mediated one-pot synthesis of benzoxazoles or oxazoles from 2-nitrophenols or 1-aryl-2-nitroethanones

One-pot reduction-triggered heterocyclizations from 2-nitrophenols to benzoxazoles and from 1-aryl-2-nitroethanones to oxazoles were investigated. In the presence of indium/AcOH in benzene at reflux, 2-nitrophenols and R-C(OMe)₃ (R=H, Me, Ph) produced excellent yields of corresponding benzoxazoles within an hour. Similarly, 1-aryl-2-nitroethanones and Ph-C(OMe)₃ in the presence of indium/AcOH in acetonitrile transformed into the corresponding oxazoles with good yields.     

Synthesis of annulated gamma-carbolines and heteropolycycles by the palladium-catalyzed intramolecular annulation of alkynes

A variety of N-substituted 2-bromo-1H-indole-3-carboxaldehydes incorporating an alkyne-containing tether on the indole nitrogen have been converted to the corresponding tert-butylimines, which have been subjected to palladium-catalyzed intramolecular iminoannulation, affording various gamma-carboline derivatives with an additional ring fused across the 4- and 5-positions in good to excellent yields. When the tethered carbon-carbon triple bond is terminal or substituted with a triethylsilyl group, the iminoannulation generates a tert-butyl-gamma-carbolinium salt as the major product. The palladium-catalyzed intramolecular annulations of N-substituted 2-bromo-1H-indole-3-carboxaldehyde, methyl 2-iodo-1H-indole-3-carboxylate, and 2-iodo-3-phenyl-1H-indole containing a phenylpentynyl tether produce the corresponding heteropolycycles in moderate to good yields.     

Suzuki reaction of vinyl triflates from six- and seven-membered N-alkoxycarbonyl lactams with boronic acids and esters

The Pd(0)-catalyzed reaction of vinyl triflates from N-alkoxycarbonyl lactams with different boron compounds has been studied. The coupling reaction of alkenylboronates and arylboronic acids with six- and seven-membered lactam-derived N-alkoxycarbonyl vinyl triflates was feasible under very mild conditions in THF-water employing (Ph3P)2PdCl2 as a catalyst and Na2CO3 as a base, which provided in high yields the corresponding 6- or 7-substituted N-alkoxycarbonyl-3,4-dihydro-2H-pyridines and N-alkoxycarbonyl-2,3,4,5-tetrahydroazepines. Allylboronates reacted slower but, with vinyl triflates from delta-valerolactam, still gave acceptable yields of the coupling product. Alkylboronic acids required different reaction conditions, in particular the presence of Ag2O together with a base in anhydrous toluene and (dppf)PdCl2 as a catalyst, affording the corresponding 6-alkyl-N-alkoxycarbonyl-3,4-dihydro-2H-pyridines in high yields.     

New route to 3-alkylthiazolo[3,2-a]benzimidazole derivatives

3-Alkyl-thiazolo[3,2-a]benzimidazole derivatives are obtained in high yields via the corresponding 4-alkyl-N-3-(2-aminophenyl)-thiazoline-2-thiones which are easily prepared from 1,2-diaminobenzene, CS(2) and halogenoketones. This new route compares advantageously with the classical mercaptobenzimidazole routes in term of simplicity,isolated yields and availability of the starting materials.     

Ruthenium-catalyzed oxidation of alcohols and catechols using t-butyl hydroperoxide

Ruthenium complexes catalyze the oxidation of alcohols to the corresponding ketones or aldehydes when t-BuOOH (70% aq.) is used as an oxidant. The reactions proceed at room temperature to give the products in excellent to fairly good yields. Among the transition metal catalysts used, dichlorotris(triphenylphosphine)ruthenium (RuCl₂(PPh₃)₃) showed the highest catalytic activity. 3,5-Di-t-butylcatechol and 4-t-butylcatechol are also effectively oxidized to the corresponding 1,2-benzoquinones in the presence of a catalytic amount of RuCl₂(PPh₃)₃ at room temperature with 1.1 equiv. of t-BuOOH, in quantitative yields. Hydrogen peroxide (30% aq.) can also be employed as an oxidant to give 1,2-benzoquinones in excellent yields.     

Reaction of 2-phenyl-4-methyl-Δ2-oxazolin-5-one with imines. A convenient synthesis of 3-amido-β-lactams

Azlactone 3a reacted with furan-2-aldehyde and thiophene-2-aldehyde imines to give corresponding 3-amido-β-lactams in good yields.     

Oxidant Promoted 1,3-Dipolar Cycloaddition of Pyridinium Ylides to Chalcones for Preparation of 1-Benzoyl-2-arylindolizines

The derivatives of 1-benzoyl-2-arylindolizine were prepared in moderate yields of 41%-78% by CrO3/Et3N promoted 1,3-dipolar cycloaddition of pyridinium N-ylides and chalcones. Under the same conditions, CrO3/Et3N promoted 1,3-dipolar cycloaddition of isoquinolinium N-ylides and chalcones provided the corresponding 1-benzoyl-2-arylpyrrolo[2,1-a]isoquinolines in 45 %-61% yields.     

Radical [3+2] annulation of N-allyl-N-chlorotosylamide with alkenes via atom-transfer process

[reaction: see text]. A radical [3+2] annulation reaction with an N-centered radical has been developed. The reaction of alkenes with N-allyl-N-chlorotosylamide yields the corresponding pyrrolidine derivatives in good yields in the presence of Et3B as a radical initiator.     

Asymmetric Michael addition of formaldehyde N,N-dialkylhydrazones to alkylidene malonates

Enantiopure formaldehyde N,N-dialkylhydrazones 1 smoothly react with prochiral alkylidene malonates 2 in the presence of MgI2 to afford the corresponding Michael adducts 3 in excellent yields and good diastereoselectivities; direct racemization-free BF3.OEt2-catalyzed thiolysis of the hydrazone C=N bond affords the corresponding dithioketals 7 in optically pure or enantiomerically enriched form.     

Study on the stannous halides promoted addition of 1,1,1-trichloro-2,2,2-trifluoroethane to aldehydes and the chemical transformation thereof

Promoted by stannous salts, 1,1,1-trichloro-2,2,2-trifluoroethane reacts readily with aliphatic, aromatic, and α, β-unsaturated aldehydes giving the corresponding alcohols bearing a CF3CCl2-moiety in good to excellent yields. These alcohols are farther oxidized by Jones reagent giving the corresponding ketones in high yields.     

Phosphine-catalyzed [3 + 2] cycloaddition of allenoates with trifluoromethylketones: synthesis of dihydrofurans and tetrahydrofurans

The triphenylphosphine-catalyzed formal [3 + 2] cycloaddition of allenoates and trifluoromethylketones was realized to give the corresponding dihydrofurans in good yields with excellent γ-regioselectivities. Hydrogenation of the dihydrofurans gave 2,4,4-trisubstituted tetrahydrofurans in good yields with exclusive cis-selectivities.