Synthesis of tetramic acids with a benzo[f]indolizine skeleton. Transannular rearrangements in pyrazino[1,2-b]isoquinolin-4-ones

Pyrazino[1,2-b]isoquinoline-1,4-diones (3) having a bulky activating group at the N(2)-position were rearranged to tetramic acids with a benzo[f]indolizine skeleton (8) in the presence of K^tBuO or LHMDS as bases. This rearrangement was diasteroselective for the 6,11a-trans-isomers of the starting compounds. 1-Hydroxy-pyrazino[1,2-b]isoquinolin-4-one (7) afforded a 1-trichloroacetamido derivative (14) after treatment with trichloroacetonitrile and a catalytic amount of sodium hydride as a base, through two subsequent base-promoted transannular rearrangements. In summary, the combination of functions in the piperazine ring of the starting tricyclic compounds conferred to them new reactivities that imply different base-promoted transannular rearrangements and led to unexpected transformations.     

Synthesis and rearrangement of cycloalkyl[1,2-e]oxazolo[3,2-a]pyrimidin-8/9-ones: an access to cycloalkyl[1,2-d]oxazolo[3,2-a]pyrimidin-5-ones

2-Substituted-4a-hydroxy-9H-cycloalkyl[1,2-e]oxazolo[3,2-a]pyrimidin-9-ones 2a-c were synthesized by an one-step cyclocondensation from the 5-substituted-2-amino-2-oxazolines 1a-c with ethyl 2-oxocyclohexanecarboxylate in ethanol at room temperature, and easily dehydrated to provide 2-substituted-9H-cycloalkyl[1,2-e]oxazolo[3,2-a]pyrimidin-9-ones 3. In refluxing xylene, the reaction conducted with various ethyl 2-oxocycloalkanecarboxylates led to the two isomeric 2-substituted-8/9H-cycloalkyl[1,2-e]oxazolo[3,2-a]pyrimidin-8/9-ones 3 and 2-substituted-5H-cycloalkyl[1,2-d]oxazolo[3,2-a]pyrimidin-5-ones 4. The structure of some compounds was unambiguously established using X-ray crystallography. According to results from the DSC analysis of compound 2a, formation of the thermodynamically stable pyrimidinones 4 could be related to an intramolecular rearrangement of kinetically controlled pyrimidinones 3.     

Microwave assisted synthesis of novel imidazo [2,1-b]thiazole derivative attached to quinoxalinones

3-(6-Phenylimidazo[2,1-b]thiazol-5-yl)quinoxalin-2(1H)-ones (qunoxalinone) (6a-q) have been synthesized by the reaction of ethyl 2-oxo-2-(6-phenylimidazo[2,1-b]thiazol-5-yl)acetates (4a-e) with suitably substituted o-phenylenediamines (5a-f) under microwave heating. The ethyl 2-oxo-2-(6-phenylimidazo[2,1-b]thiazol-5-yl)acetates (4a-e) were prepared by the reaction of 6-phenylimidazo[2,1-b]thiazoles (3a-e) with ethyl chlorooxoacetate in refluxing 1,4-dioxane whereas the thiazoles (3a-e) were synthesized by the reaction of 2-bromo-1-phenylethanones (2a-e) with thiazol-2-amine in refluxing acetone.     

Substituted coumarin amidines: useful building blocks for the preparation of [1]benzopyrano[4,3-b]pyridin-5-one and [1]benzopyrano[4,3-d]pyrimidin-5-one derivatives

The synthesis of [1]benzopyrano[4,3-b]pyridin-5-ones 4a-f and 4g-j starting from 3-formylcoumarin and 3-cyanocoumarin N-functionalized amidines 3a-f and 3g-j, respectively, was reported. The ring-closure reaction mechanism, under basic or acidic media, was proposed. Furthermore, the reaction of 3-formylamidines 3a,c-f with ammonium acetate gave good yields of 2-substituted [1]benzopyrano[4,3-d]pyrimidin-5-ones 7.     

Efficient synthesis and structural analysis of new dioxopiperazine isoquinolines

We report herein the synthesis of new dioxopiperazine isoquinolines using the Pictet-Spengler cyclisation. Our synthetic strategy for the preparation of two new compounds (5, 6), with a tetrahydro-6H-pyrazino[1,2-b]isoquinoline-1,4-dione moiety was developed in only four steps. To understand better the crucial step of the synthesis reported here, theoretical calculations using semiempirical (PM3), ab initio and DFT computations were carried out on a reduced system model. The structure of chlorohydrate water solvate of tetrahydro (2-piperidinylethyl)-6H-pyrazino [1,2-b]isoquinoline-1,4-dione (6·HCl·2H₂O) was determined by X-ray diffraction. Theoretical calculations (RHF/3-21G and RB3LYP/6-31G(d)) were also performed for compound 6 neutralised with a chloride ion.     

Synthesis of 2,3-dihydroimidazo[1,2-a]pyrimidin-5(1H)-ones by the domino Michael addition retro-ene reaction of 2-alkoxyiminoimidazolidines and acetylene carboxylates

2-Alkoxyiminoimidazolidines 2-3 react with acetylene dicarboxylates and ethyl phenylpropiolate to give 8-alkoxy-imidazo[1,2-a]pyrimidin-5(3H)-ones C, which subsequently undergo a sterically induced multihetero-retro-ene fragmentation to give imidazo[1,2-a]pyrimidin-5(1H)-ones 4-7 together with formaldehyde or benzaldehyde. On the other hand, a similar reaction of 2-3 with ethyl propiolate gives corresponding 8-alkoxy-imidazo[1,2-a]pyrimidin-5(3H)-ones 8-10. The unsubstituted imidazo[1,2-a]pyrimidin-5(1H)-one 11 can be prepared by retro-ene reaction of 9 upon prolonged heating in refluxing ethanol. A direct synthetic approach to 1-formyl-7-phenyl-imidazo[1,2-a]pyrimidine-5(1H)-one 14 is reported using DMF/sulfonyl chloride as a new Vilsmeier-type N-formylating reagent.     

A novel and convenient method for the synthesis of new derivatives of pyrido[3,2-e]pyrrolo[1,2-a][1,4]diazepine-6,11-dione

A novel methodology has been developed for the efficient synthesis of 1,4-pyridopyrrolodiazepine derivatives. The key reaction is the bromination under mild conditions by NBS of compounds resulting via peptide coupling of l-proline methyl ester with 3-aminopyridine-2-carboxylic acid 1, then intramolecular cyclization in the construction of 2-bromo-6a,7,8,9-tetrahydro-5H-pyrido[3,2-e]pyrrolo[1,2-a][1,4]diazepine-6,11-dione 4. This latter is then engaged in cross-coupling reactions to generate 1,4-pyridopyrrolodiazepines derivatives 5a-m, 6a-i, 7, and 8a-c. This strategy provides an efficient method to access a library of compounds based on privileged substructures that are of great interest in drug discovery.     

An efficient synthesis of (E)-(2-arylpyrazino[1,2-a]pyrimidine-4-ylidene)acetonitriles and cyanomethyl appended pyrimidines

A series of (E)-(2-arylpyrazino[1,2-a]pyrimidine-4-ylidene)acetonitriles 5a-j and aryl/heteroaryl tethered pyrimidin-4-yl acetonitriles 6a-e has been synthesized in excellent yields through base catalyzed ring transformation of suitably functionalized 2H-pyran-2-ones 3 using 2-aminopyrazine 4a and arylamidinium salts 4b, separately.     

An innovative approach to the synthesis of annelated [a]diaza-anthracenones through tandem cyclization

An innovative route for the synthesis of a novel class of 4-aryl-11-oxo-1,2,3,11-tetrahydro-1,3a-diazacyclopenta[a]anthracene-6-carbonitriles 5a-h and 5-aryl-12-oxo-1,3,4,12-tetrahydro-2H-1,4a-diazabenzo[a]anthracene-7-carbonitriles 5i-k has been developed by ring transformation of suitably functionalized 2H-pyran-2-ones 1 with α-oxoketene cyclic aminals 2 to give compounds 4 followed by photo-induced cyclization.     

Synthesis of phthalascidin analogs

We report a new approach to obtain phthalascidin analogs. 6-Phthalimidomethylpyrazino[1,2-b]isoquinoline-1,4-dione (5a) was obtained in a one-pot N-alkylation/cyclization of the corresponding 1-acetyl-3-arylmethyl-2,5-piperazinedione with N-phthalylacetaldehyde dimethyl acetal. Chemoselective reduction of the C(1)-carbonyl group in the 3-arylmethyl-11,11a-dehydroderivative 9a was followed by cyclization of an acyliminium intermediate, to give the 6,15-imino-7-oxo-14,14a-dehydroisoquino[3,2-b]3-benzazocin 11a. Alternatively, the octacyclic compound 13a was obtained through a novel double cyclization of a precursor in which the C(1)-carbonyl and one phthalimide carbonyl group were reduced.     

Preparation of 6-chloropyrazolo[3,4-b]pyridine-5-carbaldehydes by Vilsmeier-Haack reaction and its use in the synthesis of heterocyclic chalcones and dipyrazolopyridines

Novel 6-chloropyrazolo[3,4-b]pyridine-5-carbaldehydes 5 have been synthesized from the 4,5-dihydropyrazolo[3,4-b]pyridine-6-ones 4 via Vilsmeier-Haack reaction. Further treatment of carbaldehydes 5 with acetophenones 6 and hydrazine hydrate afforded chalcone analogues 7 and dipyrazolo[3,4-b:4′,3′-e]pyridines 8, respectively.     

Synthesis of new tetracyclic 7-oxo-pyrido[3,2,1-de]acridine derivatives

A series of (±)3-hydroxyl- and 2,3-dihydroxy-2,3-dihydro-7-oxopyrido[3,2,1-de]acridines were synthesized for antitumor evaluation. These agents can be considered as analogues of glyfoline or (±)1,2-dihydroxyacronycine derivatives. The key intermediates, 3,7-dioxopyrido[3,2,1-de]acridines (15a,b or 24a,b), for constructing the target compounds were synthesized either from 3-(N,N-diphenylamino)propionic acid (14a,b) by treating with Eaton’s reagent (P₂O₅/MsOH) (Method 1) or from (9-oxo-9H-acridin-10-yl)propionic acid (23a-c) via ring cyclization under the same reaction conditions (Method 2). Compounds 15a,b and 24a,b were converted into (±)3-hydroxy derivatives (25a-d), which were then further transformed into pyrido[3,2,1-de]acridin-7-one (28a-d) by treating with methanesulfonic anhydride in pyridine via dehydration. 1,2-Dihydroxylation of 28a-d afforded (±)cis-2,3-dihydroxy-7-oxopyrido[3,2,1-de]acridine (29a-d). Derivatives of (±)3-hydroxy (25a,b) and (±)cis-2,3-dihydroxy (29a-d) were further converted into their O-acetyl congeners 26a,b and 30a-d, respectively. We also synthesized 2,3-cyclic carbonate (31, 32, and 33) from 29a-c. The anti-proliferative study revealed that these agents exhibited low cytotoxicity in inhibiting human lymphoblastic leukemia CCRF-CEM cell growth in culture.     

A facile route to phenyl, phenylsulfanyl and phenylselanyl substituted pyrano[3,2-c]chromenes

The synthesis of phenyl, phenylsulfanyl and phenylselanyl substituted pyrano[3,2-c]chromenes 4 is accomplished via cyclocondensation of 4-oxo-4H-chromen-3-carbaldehydes 1 with appropriately substituted acetic acids 2 under mild conditions. Further treatment of 4 with alcohol or water led to 5-alkoxy- and 5-hydroxy-2H,5H-pyrano[3,2-c]chromen-2-ones 5 and 6, respectively. Acid and thermal catalysed rearrangement of 4-6 gave 5-hydroxypyrano[2,3-b]chromen-2(10aH)-ones 7 and their subsequent substitution led to 5-alkoxyderivatives 8. Reaction of 4 with amides led to 5-acylamino or 5-phenylsulfonamino substituted 2H,5H-pyrano[3,2-c]chromen-2-ones 9. Reactions were performed under heating or microwave irradiation.     

Tunable blue-emitting fluorophores—benzo[1,2-b:4,3-b′]dithiophene and trithia[5]helicene end-capped with electron-rich or electron-deficient aryl substituents

Light-emitting fluorophores 1-10b based on aryl substituted benzo[1,2-b:4,3-b′]dithiophenes (BDT) and trithia[5]helicenes (T5H) have been synthesized using various combinations of Suzuki coupling, the Wittig, or McMurry reaction, and subsequent photocyclization of the dithienylethenes thus obtained. Photophysical properties of the helical compounds end-capped with different electron-rich and electron-deficient aryl moieties thus resulting were evaluated. Photocyclization of a dithienylethene derivative 10a was investigated, and the X-ray crystal structure of dinaphthyl-substituted BDT (4) was obtained. With this series of compounds 1-10b, we demonstrate that the optical properties of all of the new compounds, and by extension many conjugated materials, can be tuned over the entire blue range (400-480 nm).     

Synthesis of chromeno[4,3,2-cd]isoindolin-2-ones and chromeno[4,3,2-de]isoquinolin-3-ones. Electrophilic versus anionic cyclization of carbamates

The total synthesis of chromeno[4,3,2-cd]isoindolin-2-ones 6a-d and chromeno[4,3,2-de]isoquinolin-3-ones 15a-b from 4-methoxy-9H-xanthen-9-one is reported. The construction of the nitrogenated ring was attempted by both intramolecular electrophilic and anionic cyclizations of the corresponding carbamate precursors. Only anionic cyclization was possible for isoindolinones, but for isoquinolinones the electrophilic and anionic routes both afforded excellent yields.     

Synthesis and single-crystal X-ray diffraction analysis of new heterocyclic coloured materials. 3-Arylazo-8H-imidazo[1,2-b] pyrazolo[4,3-d]pyridazines

A simple synthetic strategy is described for the hitherto unreported 3-arylazo-8H-imidazo[1,2-b]pyrazolo[4,3-d]pyridazines 7 is described based on the reaction of 3-acetyl-4-cyano-1,5-diphenylpyrazole hydrazone 3 with the hydrazonoyl halides 1a-l. The structures of such dyes were confirmed by spectroscopic and X-ray crystallographic analyses. The mechanism of formation of such compounds was also discussed.     

An expedient approach to tetrahydrofuro[3,2-b]pyridine-2(3H)-ones via activation of pyridine N-oxide by triflic anhydride

The double addition of bis(trimethylsilyl) ketene acetals [R₁, R₂ = CH₃, -(CH₂)₅-] to pyridine N-oxide promoted by triflic anhydride under mild conditions generates N-[(trifluoromethane)sulfonyl-1,2-dihydropyridine-2,4-dicarboxylic acids 2a-b. Subsequent reaction of these acids upon iodolactonization conditions affords tetrahydrofuro[3,2-b]pyridine-2(3H)-ones 3a-b containing an exo-insaturation on the products as a result of an unexpected decarboxylation.     

A new synthetic entry to the tricyclic skeleton of FR901483 by palladium-catalyzed cyclization of vinyl bromides with ketone enolates

A new synthetic entry to the FR901483 core is described. The Pd-mediated cyclization of amino-tethered vinyl halides and ketone enolates from the azaspiro[4.5]decan-8-ones 5 and 10 gives the functionalized 7,10a-methanoperhydropyrrolo[1,2-a]azocines 1 and 11, respectively.     

A novel transformation of 1-exo-substituted 2a-aroyl-1,2,2a,8b-tetrahydro-3H-benzo[b]cyclobuta[d]pyran-3-ones with sulfoxonium ylide to highly strained 2a-(1-arylethenyl)-1,2,2a,7b-tetrahydrocyclobuta[b]benzofurans

When 1-substituted 2a-aroyl-1,2,2a,8b-tetrahydro-3H-benzo[b]cyclobuta[d]pyran-3-ones (1) were treated with dimethylsulfoxonium methylide, 1-endo isomers (endo-1) gave 1-substituted 3-aroyl-1,2,4a,9b-tetrahydrodibenzofuran-4-ols (2) exclusively as expected. On the other hand, 1-exo isomers (exo-1) underwent a novel transformation to 1-substituted 2a-(1-arylethenyl)-1,2,2a,7b-tetrahydrocyclobuta[b]benzofurans (3), together with 2.     

Synthesis of new compounds containing the 2,3-dihydro[1,4]dioxino[2,3-b]pyridine heterocyclic system as a substructure

2,3-Dihydro-spiro[1,4]dioxino[2,3-b]pyridine-3,3′-pyrrolidine (8A) and 2,3-dihydro-spiro[1,4]dioxino[2,3-b]pyridine-3,4′-piperidine (9A) have been synthesized from 2-chloro-3-pyridinol. The corresponding 2,3′ (8B) and 2,4′ (9B) isomers were obtained via the Smiles rearrangement, while 9B was also selectively synthesized from 2-nitro-3-pyridinol. The separation of the isomers A and B under the sulfamide form was carried out by flash column chromatography. Subsequent transformations of the corresponding dioxinopyridine derivatives were described.