A scalable Nenitzescu synthesis of 2‐methyl‐4‐(trifluoromethyl)‐1H‐indole‐5‐carbonitrile

2‐Methyl‐4‐(trifluoromethyl)‐1H‐indole‐5‐carbonitrile is a key intermediate in the synthesis of selective androgen receptor modulators discovered in these laboratories. A practical and convergent synthesis of the title compound starting from 4‐nitro‐3‐(trifluoromethyl)phenol and tert‐butyl acetoacetate was developed, including a telescoped procedure for synthesis (without isolation) and Nenitzescu reaction of 2‐trifluoromethyl‐1,4‐benzoquinone. Conversion of the known Nenitzescu indole product to a novel triflate intermediate followed by palladium‐catalyzed cyanation afforded a penultimate carbonitrile. Removal of the C‐3 tert‐butyl ester group on the indole through a decarboxylative pathway completed the synthesis of the title compound in six steps (27% overall yield) from 4‐nitro‐3‐(trifluoromethyl)phenol (five steps, 37% overall yield from tert‐butyl acetoacetate). J. Heterocyclic Chem., (2011).     

Asymmetric Proline‐Catalyzed Addition of Aldehydes to 3H‐Indol‐3‐ones: Enantioselective Synthesis of 2,3‐Dihydro‐1H‐indol‐3‐ones with Quaternary Stereogenic Centers

The proline‐catalyzed addition of various aliphatic aldehydes to sterically hindered 2‐aryl‐substituted 3H‐indol‐3‐ones affords 2,2‐disubstituted 2,3‐dihydro‐1H‐indol‐3‐one derivatives with excellent enantioselectivities. In addition, the synthesis of a chiral derivative, (S)‐2‐(2‐bromophenyl)‐2,3‐dihydro‐2‐(2‐hydroxyethyl)‐1H‐indol‐3‐one, which can be used as an intermediate for the preparation of the natural product hinckdentine A was accomplished with a high level of enantioselectivity.     

Synthesis of 3,4‐dihydro‐1(2H)‐isoquinolinonesxs

Approaches toward the preparative‐scale synthesis of target 3,4‐dihydro‐1(2H)‐isoquinolinones 1–3 are presented. Compounds 1 and 2 were prepared via a Schmidt rearrangement on easily obtained indanone precursors, but in low overall yield. A better method to make this class of compounds is exemplified by the large‐scale synthesis of 2 via a Curtius rearrangement sequence. Thus, high‐temperature thermal cyclization of an in situ formed styryl isocyanate from precursor 8 in the presence of tributylamine gave the corresponding 1(2H)‐isoquinolinone ( 9 ). Catalytic hydrogenation of 9 provided the desired 3,4‐dihydro‐5‐methyl‐1(2H)‐isoquinolinone ( 2 ) in 65 % overall yield. Similar reduction of a commercially available 5‐hydroxy‐1(2H)‐isoquinolinone precursor 10 followed by an O ‐alkylation/amination sequence gave target 3 in good overall yield. The route proceeding via the Curtius rearrangement is recommended for large scale synthesis of other 3,4‐dihydro‐1(2H)‐isoquinolinones. Only when deactivating substituents or sensitive functionality within the benzenoid ring render the high temperature ring closure of the intermediate isocyanate inefficient might a Schmidt rearrangement protocol be the method of choice.     

First Total Synthesis of N‐(3‐Guanidinopropyl)‐2‐(4‐hydroxyphenyl)‐2‐oxoacetamide

The first total synthesis of the α‐oxo amide‐based natural product, N‐(3‐guanidinopropyl)‐2‐(4‐hydroxyphenyl)‐2‐oxoacetamide ( 3 ), isolated from aqueous extracts of hydroid Campanularia sp., has been achieved. The α‐oxo amide 12 , prepared via the oxidative amidation of 1‐[4‐(benzyloxy)phenyl]‐2,2‐dibromoethanone ( 9a ) with 4‐{[(tert‐butyl)(dimethyl)silyl]oxy}butan‐1‐amine ( 10a ), has been used as the key intermediate in the total synthesis of 3 as HBr salt. On the way, an expeditious total synthesis of polyandrocarpamide C ( 2c ), isolated from marine ascidian Polyandrocarpa sp., was carried out in four steps.     

A Simple Synthesis of 5‐(2‐Aminophenyl)‐1H‐pyrazoles

A four‐step synthesis of 1‐substituted 5‐(2‐aminophenyl)‐1H‐pyrazoles 5 as a novel type of histamine analogs and versatile building blocks for further transformations was developed. The synthesis starts from commercially available 2‐nitroacetophenone ( 12 ), which is converted into the enamino ketone 13 as the key intermediate. Cyclization of the key intermediate 13 with monosubstituted hydrazines 14a – 14l afforded the 5‐(2‐nitrophenyl)‐1H‐pyrazoles 17a – 17l . Finally, catalytic hydrogenation of the nitro compounds 17a, 17c – 17e , and 17g – 17j furnished the title compounds 5a, 5c – 5e , and 5g – 5j , respectively, in good yields. As demonstrated by some further transformations, additional functionalization of compounds 17 and 5 is feasible, either by electrophilic substitution at C(4) of the pyrazole ring, or at the NH₂ group.     

Synthesis of Some Novel 4‐(Furan‐2‐yl)‐5,6‐dimethylpyridines

N‐2‐amino‐4‐(furan‐2‐yl)‐5,6‐dimethylnicotinonitrile ( 4 ) was utilized as key intermediate for the synthesis of some new, pyridopyrimidine, benzo[1,5][g]oxazocine, naphthoquinone, and isoindole derivatives. The structures of the newly synthesized compounds were confirmed by elemental analysis, IR, ¹H‐NMR, and mass spectral data.     

A Facile Synthesis of Novel (Z)‐ethyl‐3‐(5‐substituted‐1‐alkyl/aryl‐1H‐indol‐3‐yl)‐2‐(1H‐tetrazol‐5‐yl)acrylate

A novel route was developed for synthesis of high potential 1H‐tetrazoles by using conventional method. Tetrazole scaffold is a promising pharmacophore fragment, frequently used in the development of various novel drugs. Here, the novel (Z)‐3‐(N‐alkyl‐indol‐3‐yl)‐2‐(1H‐tetrazole‐5‐yl)acrylates 5 ( a – i ) have been synthesized from (Z)‐ethyl‐3‐(1H‐indol‐3‐yl)2‐(1H‐tetrazol‐5‐yl)acrylates 4 ( a – c ) by using various alkylating agents such as Dimethyl Sulphate (DMS), Diethyl Sulphate (DES), and benzyl chloride; 4 ( a – c ) were synthesized from sodium azide in the presence of copper sulfate in dimethylformamide; 3 ( a – c ) have been prepared by Knoevenagel condensation of indole‐3‐carbaldehyde 1 ( a – c ) and ethylcyanoacetate 2 in the presence of L‐Proline as a catalyst at room temperature in ethanol for an hour. This is an efficient and clean click chemistry method that has various advantages such as easy workup, higher yields, shorter reaction times, and more economical.     

A Facile and Efficient Synthesis of Arylsulfonamido‐Substituted 1,5‐Benzodiazepines and N‐[2‐(3‐Benzoylthioureido)aryl]‐3‐oxobutanamide Derivatives

A facile and efficient synthesis of 1,5‐benzodiazepines with an arylsulfonamido substituent at C(3) is described. 1,5‐Benzodiazepine, derived from the condensation of benzene‐1,2‐diamine and diketene, reacts with an arylsulfonyl isocyanate via an enamine intermediate to produce the title compounds of potential synthetic and pharmacological interest in good yields (Scheme 1). In addition, reaction of benzene‐1,2‐diamine and diketene in the presence of benzoyl isothiocyanate leads to N‐[2‐(3‐benzoylthioureido)aryl]‐3‐oxobutanamide derivatives (Scheme 2). This reaction proceeds via an imine intermediate and ring opening of diazepine. The structures were corroborated spectroscopically (IR, ¹H‐ and ¹³C‐NMR, and EI‐MS) and by elemental analyses. A plausible mechanism for this type of cyclization is proposed (Scheme 3).     

Synthesis of pyrimido[1,2‐a]benzimidazol‐4(10H)‐one derivatives and evaluation of their interactions with DNA

The synthesis of new derivatives of the planar tricyclic pyrimido[1,2‐a]benzimidazole system featuring protonable side chains in the 3 and/or 10 positions is described. The reported literature procedures for the preparation of the intermediate 3‐ethoxycarbonylpyrimido[1,2‐a]benzimidazol‐4(10H)‐one 15 , starting from 2‐aminobenzimidazole 18 and diethyl ethoxymethylenemalonate, were revised. The interaction with DNA, the intrinsic binding constants, and the antiproliferative activity of a number of compounds ( 1–8, 10, 11 ) were preliminarly investigated.     

Synthesis of the Natural Product Building Block 5‐(3‐Bromophenyl)‐4‐hydroxy‐5‐methylhexan‐2‐one and its Chiral Characterization by Using Chiroptical Spectroscopy

The absolute configuration of 5‐(3‐bromophenyl)‐4‐hydroxy‐5‐methylhexan‐2‐one, an intermediate in the synthesis of various natural products, is assigned by using vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and optical rotatory dispersion (ORD). Experimental spectra were compared to density functional theory (DFT) calculations of the molecule with known configuration. These three techniques independently confirm that the absolute configuration is (S)‐5‐(3‐bromophenyl)‐4‐hydroxy‐5‐methylhexan‐2‐one, thus enabling us to assign the absolute configuration with high reliability. The reliability of the VCD analysis was assessed quantitatively by using the CompareVOA program. We found that, in cases in which the agreement between theory and experiment was very good, a value of 10 cm^?1 for the triangular weighting function gave a more‐realistic discriminative power between enantiomers than the default value of 20 cm^?1.     

A Green Synthesis of 2‐Amino‐4‐(9H‐carbazole‐3‐yl)thiophene‐3‐carbonitriles by a Step‐wise and One‐pot Three‐component Gewald Reaction

An eco‐friendly method has been developed for the synthesis of 2‐amino‐4‐(9H‐carbazole‐3‐yl)thiophene‐3‐carbonitriles from preliminary carbazole ( 1 ) through an intermediate of 2‐(1‐(9H‐carbazole‐3‐yl)ethylidene)malononitriles using the Knoevenagel condensation followed by the Gewald reaction. On the other hand, the target compounds could also be prepared in a one‐pot three‐component manner by treating equimolar quantities of 1‐(9H‐carbazole‐3‐yl)ethanone ( 3 ), malononitrile, and elemental sulfur. The merits of this preparation are mild reaction conditions. The Gewald reaction is executed with inorganic base NaHCO₃ (H₂O) in tetrahydrofuran, easy work‐up procedure with good yields.     

Synthesis of 15‐Cyano‐12‐oxopentadecano‐15‐lactone and 15‐Cyano‐ 12‐oxopentadecano‐15‐lactam

15‐Cyano‐12‐oxopentadecano‐15‐lactone was synthesized in 59% total yield starting from 2‐nitrocyclododecanone by Michael addition to acrylaldehyde, followed by reaction with trimethylsilylcyanide, hydrolysis, ring‐expansion, and Nef reaction. A two‐step, one‐pot synthesis of intermediate 2‐hydroxy‐4‐(1‐nitro‐2‐oxycyclododecyl)butanenitrile from 3‐(1‐nitro‐2‐oxocyclododecyl)propanal was developed and the conditions for the Nef reaction were studied. 15‐Cyano‐12‐oxopentadecano‐15‐lactam was synthesized in 40% total yield starting from 2‐nitrocyclododecanone by Michael addition to acrylaldehyde, followed by Strecker reaction, ring‐expansion, and Nef reaction. The conditions for the Strecker and Nef reactions were studied. The structures of the target compounds, intermediates, and by‐product were characterized by IR, ¹H‐ and ¹³C‐NMR, and elemental analysis or MS.     

Synthesis and Cytotoxicity in Vitro of N‐Aryl‐4‐(tert‐butyl)‐5‐(1H‐1,2,4‐triazol‐1‐yl)thiazol‐2‐amine

A series of novel N‐aryl‐4‐(tert‐butyl)‐5‐(1H‐1,2,4‐triazol‐1‐yl)thiazol‐2‐amines synthesized in a green way. H₂O₂‐NaBr Brominating circulatory system was used in the synthesis of the key intermediate in a mild condition. All of the target compounds were confirmed by ¹H NMR and elemental analysis and tested for their cytotoxicity against two different human cancer cell lines. The cytotoxicity assay revealed that some of the title compounds showed moderate to strong cytotoxic activities. Compound 2i was the most potent compound with the IC₅₀ values of 9 μM against Hela cells and 15 μM against Bel–7402 cells, respectively.     

Synthesis and Structure of O,O‐Diethyl N‐[(trans‐4‐Aryl‐5,5‐dimethyl‐2‐oxido‐2λ5‐1,3,2‐dioxaphosphorinan‐2‐yl)methyl]phosphoramidothioates

A study on the synthesis of the novel N‐(cyclic phosphonate)‐substituted phosphoramidothioates, i.e., O,O‐diethyl N‐[(trans‐4‐aryl‐5,5‐dimethyl‐2‐oxido‐2λ⁵‐1,3,2‐dioxaphosphorinan‐2‐yl)methyl]phosphoramidothioates 4a – l , from O,O‐diethyl phosphoramidothioate ( 1 ), a benzaldehyde or ketone 2 , and a 1,3,2‐dioxaphosphorinane 2‐oxide 3 was carried out (Scheme 1 and Table 1). Some of their stereoisomers were isolated, and their structure was established. The presence of acetyl chloride was essential for this reaction and accelerated the process of intramolecular dehydration of intermediate 5 forming the corresponding Schiff base 7 (Scheme 2).     

Synthesis of 2‐Substituted 2‐Amino Ketones by Rhodium‐Catalyzed Reaction of N‐Sulfonyl‐1,2,3‐triazoles with 2‐Alkenols

A study on a rhodium(II )‐catalyzed reaction of N‐sulfonyl‐1,2,3‐triazoles with 2‐alkenols is reported. The reaction is initiated by insertion of an α‐imino carbene into the O–H linkage of alcohol, forming a 2‐alkenoxy enamide intermediate. A thermal [3,3]‐sigmatropic rearrangement follows to yield 2‐substituted 2‐amino ketone in a stereoselective manner. The successful application of this methodology to a formal synthesis of (–)‐α‐conhydrine is also described.     

Synthesis of N‐aryl‐2‐amino‐4‐oxo‐3,4‐dihydrothieno[2,3‐d]pyrimidine‐6‐carboxamides

Synthetic routes for the preparation of methyl 2‐amino‐4‐methoxythieno[2,3‐d]pyrimidine‐6‐carboxylate (4) ‐ useful intermediate for lipophilic and classical antifolates from 2‐amino‐4,6‐dichloropyrimidine‐5‐car‐baldehyde (1) have been studied. It has been shown that more efficient synthesis of compound 4 includes the preparation of 4‐methoxy derivative 7 and subsequent tandem substitution/annulation reaction with methyl mercaptoethanoate in dimethylformamide in the presence of potassium carbonate and molecular sieves 4 Å. Compound 4 was used for the synthesis of N‐aryl 2‐amino‐4‐oxo‐3,4‐dihydrothieno[2,3‐d]‐pyrimidine‐6‐carboxamides 10a‐c, including an analog of folic acid with amide bridge ‐ N‐(4‐{[(2‐amino‐4‐oxo‐3,4‐dihydrothieno[2,3‐d]pyrirnidin‐6‐yl)carbonyl]amino}‐benzoyl)‐L‐glutamic acid (10c) .     

Cu‐Catalyzed Aerobic Oxidative Cyclizations of 3‐N‐Hydroxyamino‐1,2‐propadienes with Alcohols,Thiols, and Amines To Form α‐O‐, S‐, and N‐Substituted 4‐Methylquinoline Derivatives

A one‐pot, two‐step synthesis of α‐O‐, S‐, and N‐substituted 4‐methylquinoline derivatives through Cu‐catalyzed aerobic oxidations of N‐hydroxyaminoallenes with alcohols, thiols, and amines is described. This reaction sequence involves an initial oxidation of N‐hydroxyaminoallenes with NuH (Nu=OH, OR, NHR, and SR) to form 3‐substituted 2‐en‐1‐ones, followed by Brønsted acid catalyzed intramolecular cyclizations of the resulting products. Our mechanistic analysis suggests that the reactions proceed through a radical‐type mechanism rather than a typical nitrone‐intermediate route. The utility of this new Cu‐catalyzed reaction is shown by its applicability to the synthesis of several 2‐amino‐4‐methylquinoline derivatives, which are known to be key precursors to several bioactive molecules.     

Practical Synthesis of (20S)‐10‐(3‐Aminopropyloxy)‐7‐ethylcamptothecin,a Water‐Soluble Analogue of Camptothecin

A robust, practical synthesis of (20S)‐10‐(3‐aminopropyloxy)‐7‐ethylcamptothecin (T‐2513, 5 ), which is a water‐soluble analogue of camptothecin, has been developed. The key step in this synthesis is a highly diastereoselective ethylation at the C20 position by using N‐arylsulfonyl‐(R)‐1,2,3,4‐tetrahydroisoquinoline‐3‐carboxylic acid ester as a chiral auxiliary, which affords the key intermediate ethyl‐(S)‐2‐acyloxy‐2‐(6‐cyano‐5‐oxo‐1,2,3,5‐tetrahydroindolizin‐7‐yl)butanoate ( 8 k ) in 93 % yield and 87 % de. Optically pure compound 8 k was obtained by a single recrystallization from acetone and its further elaboration through Friedlander condensation afforded compound 5 . This synthesis does not require any chromatographic purification steps and can provide compound 5 on a multi‐gram scale in 6.3 % overall yield (16 steps).     

trans‐3‐Ethyl‐cis‐2,6,6‐trimethyl‐4‐oxocyclohexanecarboxylic acid: an intermediate in the synthesis of a highly potent estrogen

The title compound, C₁₂H₂₀O₃, (IV), the ethyl ester of which is an intermediate in the synthesis of a compound reported to be highly estrogenic, has been prepared. After the initial steps reported for the synthesis of this ester intermediate were followed, it was converted into the crystalline acid, (IV), for X‐ray analysis. It was verified that (IV) was racemic when prepared. X‐ray analysis showed that anti‐hydrogenation of the double bond had occurred in the synthesis, making the orientation of the carboxyl group cis to the 2‐methyl group and trans to the 3‐ethyl group. NMR spectroscopy showed that the stereochemistry of (IV) was identical with that of its ester precursor. While the earlier report did not note the stereochemistry of this ester, it pointed out that the estrogenic product derived from it possessed the opposite carboxyl‐2‐methyl orientation, i.e.trans, although no X‐ray analysis was performed. In the light of these results and the importance of correlating biological activity with compound structure, the unequivocal characterization of the highly estrogenic compound is warranted.     

Thermal Synthesis of 3‐Bromothieno[3,2‐c]pyridin‐4‐(5H)‐one: A Telescoped Procedure with Tributylamine

3‐Bromothieno[3,2‐c]pyridine‐4‐(5H)‐one ( 1 ) was prepared from (2E)‐3‐(4‐bromo‐2‐thienyl)‐2‐propenoic acid ( 3 ) by the Eloy–Deryckere thermal benzo/heteropyridinone synthesis. A telescoped procedure was developed, which reduces some of the risk associated with the classic procedure. Use of tributylamine as an additive in this process was shown to facilitate E/Z‐isomerization of the intermediate vinyl isocyanate and lower the temperature necessary for the overall thermal process.