Synthesis of Novel Fluorinated 11H‐Azaindolo[3,2‐c]isoquinolines

A series of novel fluorinated 11H‐azaindolo[3,2‐c]isoquinolines ( 7 ) have been synthesized starting from 2(1H)pyridones ( 1 ) via azaindoles ( 5 ). Initially, compound 1 was treated with POCl₃/DMF, and the resulting compound 2 was reacted with benzylamine to obtain compounds 3 that were subjected to cyclization after protecting the secondary amine to get azaindoles ( 5 ). Further, compounds 5 were subjected to cyclization as per Pictet–Spengler reaction condition. However, it was not successful. Subsequently, the azaindoles ( 5 ) were acetylated and then cyclized to give title compounds 7 . These compounds are new and well characterized by spectral data.     

Photoinduced Electron Transfer Reactions of alpha-Cyclopropyl- and alpha-Epoxy Ketones. Tandem Fragmentation-Cyclization to Bi-, Tri-, and Spirocyclic Ketones

Reductive photoinduced electron transfer (PET) reactions have been performed with various bicyclic alpha-cyclopropyl-substituted ketones and tertiary amines. The reaction resulted in a regioselective cleavage of one cyclopropyl bond under formation of an exocyclic radical with an endocyclic enolate unit. In the case of bicyclic ketones with an unsaturated side chain, various bicyclic, spirocyclic, and tricyclic products are accessible via radical cyclization, depending on the position of the alkenyl substituent. In addition to triethylamine, N-silylated amines have also been used as electron donors, leading to a variety of compounds, among them are silylated fragmentation products, indicating that a proton is transferred from not only the amine radical cation but also the cationic silyl group. The intramolecular Paternó-Büchi reaction has also been studied for cyclopropane derivatives of the jasmone type leading to tetracyclic oxetanes. Finally, alpha-epoxy-substituted ketones have been investigated under PET conditions, yielding ring-opened products.     

Lewis acid-catalyzed conjugate addition-cyclization reactions of ethenetricarboxylates with substituted propargyl alcohols: stereoselectivity in the efficient one-pot synthesis of methylenetetrahydrofurans

Oxygen-containing heterocyclic systems are important structures in organic chemistry because of their presence in many biologically active compounds. In this work, a Lewis acid-catalyzed cyclization of ethenetricarboxylate derivatives 1 with substituted propargyl alcohols to give methylenetetrahydrofurans was investigated. Reaction of 1 and gamma-silicon-substituted propargyl alcohols 4 with ZnBr2 at 80-110 degrees C led to (Z)-silicon-substituted products stereoselectively. Reaction of 1 and gamma-ester-substituted propargyl alcohol 7 in the presence of various Lewis acids gave ester-substituted methylenetetrahydrofurans stereoselectively. Interesting Lewis acid dependency on stereoselectivity for the reaction of 7 was found. Reaction of alpha-substituted propargyl alcohols also gave cyclized products.     

Synthesis of dibenzo[g,p]chrysenes from bis(biaryl)acetylenes via sequential ICl-induced cyclization and Mizoroki-Heck coupling

We report a facile synthesis of functionalized dibenzo[g,p]chrysenes via initial ICl-promoted cyclization of bis(biaryl)acetylenes, followed by the Mizoroki-Heck coupling reaction. This new approach works well for various bis(biaryl)acetylenes to afford dibenzo[g,p]chrysenes bearing various functionalities. With substrates of one special type including 4'-methoxy-2-ethynylbiphenyls, we found that the ICl treatment led to ipso cyclization to give bicyclic spirocyclohexadienones. In the presence of MeOH/H2SO4, these spiroketone products undergo rearrangement to give 9-iodophenanthrenes through a selective 1,2-alkenyl migration. We prepared various 4'-methoxy-2-ethynylbiphenyl compounds to show the generalization of such an ipso cyclization and 1,2-alkenyl shift. This ipso-cyclization approach can be extended to the preparation of dibenzo[g,p]chrysenes.     

A facile route to the synthesis of pyrimido[2,1-b]quinazoline core from the primary allyl amines afforded from Baylis–Hillman adducts

A highly simplified approach for the generation of substituted pyrimido[2,1-b]quinazoline core from the primary allyl amines afforded from the Baylis–Hillman adducts is described. Sequential reductive alkylation of the primary allyl amine with 2-nitrobenzaldehyde, reduction of the aromatic nitro group with In, CNBr-promoted intramolecular cyclization followed by NaOMe-mediated another intramolecular cyclization furnish the title compounds.     

Synthesis of bicyclic pyrane derivatives via tungsten-mediated [3 + 3] cycloaddition of epoxides with tethered alkynes.

Propargyltungsten compounds bearing a tethered epoxide were prepared in short steps from readily available materials. In the presence of various Lewis acids, BF(3).Et(2)O catalysts (25 mol %) most effectively promote the [3 + 3] cycloaddition of the epoxide with its tethered propargyltungsten group, delivering bicyclic pyranyltungsten compounds in reasonable yields. This cyclization proceeds highly diastereoselectively with tolerance of various functional groups. The stereochemical outcome indicates that the cycloaddition is initiated by the ring opening of the epoxides via an exo-attack of the propargyltungsten group. The resulting pyranyltungsten organometallics were demetalated to yield various bicyclic pyranyl derivatives using different oxidants. This new method provides a short enantiospecific synthesis of bicyclic oxygen compounds if chiral epoxide is used in the cyclization. A mechanistic model is presented to rationalize the reaction pathway of this [3 + 3] cycloaddition.     

Synthesis of 2- and 3-substituted-1,2,3,4-tetrahydrodibenzo[f,h]isoquinolines

Some 2- and 3-substituted-1,2,3,4-tetrahydrodibenzo[f,h]isoquinolines were prepared by a synthetic scheme involving a selective Borch reduction of an amide to the corresponding amine and a Friedel-Crafts cyclization to obtain the dibenzo[f,h]isoquinoline system. The title compounds, which have a similarity to the cell growth inhibitory alkaloid cryptopleurine, failed to exhibit significant protein synthesis inhibitory activity.     

Synthesis of (−)-Hobartine and Related Indole Alkaloids

An improved method for obtaining optically pure (S)-(l-p-menthen-8-yl)amine ( 12 ) has led to expedient syntheses of two hypothetical biogenetic intermediates on the way to aistoteline ( 7 ), namely (S)-(N)-(l-p-menthen-8-yl)-2-(3-indolyl)ethylamine ( 3 ) and (S)-(N)-(l-p-menthen-8-yl)-2-(3-indolyl)ethylideneamine ( 4 ). The latter has been transformed into (?)-hobartine ( 6 ) in 64% yield via a stereoselective biomimetic cyclization by treatment with HCOOH. This unambiguous synthesis establishes the hitherto unknown absolute configuration of (?)-hobartin ( 6 ). Several model cyclization reactions of N-substituted α-(terpen-8-yl)imine derivatives yielding unsaturated 3azabicyclo [3.3.1]nonane compounds are described.     

Synthesis of highly functionalized strained bicyclic dilactam derivatives

An efficient and modest protocol has been utilized for the synthesis of bicyclic dilactam derivatives through one-pot multicomponent domino reaction starting from various cyclic ketones under mild condition. The synthesized motif shows four stereogenic centers with two quaternary amine functionalities and such molecular arrangements are very fascinating and rare to obtain. We propose a mechanism for the formation of bicyclic dilactams through aldol condensation/condensation of cyanoacetamides/cyclization of condensed intermediate.     

Novel cyclization reactions of mono- and dichloroazodienes. A new synthesis of substituted pyridazines

Cyclization of the in—situ generated chloroazodienes with a variety of enamines was found to give chloro-substituted tetrahydropyridazines which could be aromatized to pyridazines by base treatment. This sequence appears to be a formal 4 + 2 hetero Diels-Alder reaction with a high degree of regio and stereo control and constitutes a new synthesis of substituted pyridazines. However, cyclization of the corresponding dichloroazodienes with acyclic enamines gave not only the expected pyridazine product, but also gave an N-aminopyrrole product. Combination of the dichloroazodiene with cyclic enamines gave bicyclic dihy-dropyridazines, bicyclic pyridazines, and acyclic enamines which could be forced to close to the bicyclic dihydropyridazines upon further heating. These results would indicate a stepwise mechanism. The scope and mechanistic speculations on these reactions will be presented. While exploring the novel cyclization reactions of 4-chloroazodienes with electron rich olefins we developed a new and general synthesis of substituted 3-phenypyridazines. A number of these analogs were found to exhibit bleaching herbicidal activity (phytoene desaturase inhibition). Further methodology development coupled with analog synthesis led to the preparation of 3-heteroaryloxy and 3-aryloxypyridazines with increased unit activity and selectivity as well as good environmental properties. These compounds were found to be more active than current commercial standards on a number of important weed species with selectivity in corn in the US and small grains in Europe. Greenhouse activity of the most active analogs ranged from 17–140 g/hectare on important narrow-leaf species.     

Stereochemical studies—75 : Saturated heterocycles—62. connection between the diastereoselectivity and the dominant conformation in the formation of condensed- skeleton 1,3-oxazines,first X-ray diffraction evidence of N-outside conformation

The rapid, spontaneous epimerization occurring at the C(2) chirality centre of a new diastereomeric (r-4,c-2,c-5)-2-(p-nitrophenyl)-3-methyl-4,5-tetramethylenetetrahydro-1,3-oxazine led to the conclusion that the configuration at C(2) of the bicyclic 1,3-oxazines formed by the cyclization of alicyclic 1,3-aminoalcohols with aldehydes is determined by the dominant conformation of the product. The first X-ray diffraction evidence is given for the N-outside conformation of compounds of this type.     

Total Synthesis of (−)‐Cephalotaxine and (−)‐Homoharringtonine via Furan Oxidation–Transannular Mannich Cyclization

Homoharringtonine and its congener cephalotaxine were synthesized. Oxidative ring‐opening of a furan unveils an amine‐tethered dicarbonyl, which undergoes spontaneous transannular Mannich cyclization. The cascade builds the full cephalotaxine substructure in a single operation in 60 % yield. A Noyori reduction enabled synthesis of the title compounds with excellent enantioselectivity (k_rel=278).     

Reactivity studies of ethyl(Z)‐N‐(2‐amino‐1,2‐dicyanovinyl) formimidate with carbonyl compounds in the presence of base

The reaction of ethyl(Z)‐N‐(2‐amino‐1,2‐dicyanovinyl)formimidate 6 with carbonyl compounds in the presence of triethyl amine occurs with formation of the Schiff s base and intramolecular hydrolysis of the adjacent cyano group to give the alkylideneamino derivatives 8a‐f . When the α‐carbon of the ketone has at least one proton, the prolonged contact of 8a‐f with triethylamine causes intramolecular cyclization between this carbon and the imidate carbon atom to form a seven membered ring. This is followed by cyclization of the cyano and amido groups, leading to the pyrrolo[4,3‐b][1,4]diazepines 9 . If a strong base is used the first ring to be formed is the pyrrole ring as evidenced in the reaction of 8a with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene leading to 14 . The subsequent addition of methyl amine to the reaction mixture, caused cleavage of the alkylideneamino unit and formation of the amidine function from the imi date ( 15 ). The addition of acid to the imidates 8a and 8f led to the diazepine compounds 10a and 10f respectively. A suspension of compound 8e in ethanol and triethylamine evolved to a pyrazinone structure 12 under kinetic conditions (4 hours, room temperature) and to the pyrrolo[4,3‐b][1,4]diazepine 9e under thermodynamic conditions (48 hours, room temperature).     

Concise synthesis of 3,7-dioxa-9-aza-bicyclo[3,3,1]-nonane

[reaction: see text] The basicity of an amine has a great impact on physicochemical properties and pharmacokinetics. To attenuate the basicity of morpholine, a bicyclic amine was designed and synthesized with the introduction of an additional beta-oxygen. A transannular cyclization and reduction of a bridgehead alpha-chloro amine functionality produces the topographically unusual amine (pKa = 6.7) in good yield.     

Total synthesis of (+)-seco-C-oleanane via stepwise controlled radical cascade cyclization

An asymmetric concise total synthesis of the (+)-seco-C-oleanane 1 was accomplished. The successful route to this natural product involves as the key step a stepwise regio- and stereocontrolled catalytic radical polyene cascade cyclization from preoleanatetraene oxide (16), a process mediated by Cp(2)TiCl. The use of this single-electron-transfer complex permits mild cyclization conditions without using unnecessary prefunctionalizations and stops the process at the bicyclic level. Theoretical data revealed high activation energy for the third ring closure, which would account for the control of the cyclization. This process also led to natural (-)-achilleol B, camelliol A, and (+)-seco-β-amyrin as minor compounds.     

5-Cyano-6-aryluracil and 2-thiouracil derivatives as potential chemotherapeutic agents. IV

A series of 5-cyano-6-aryluracils and 2-thiouracils 1a-h has been prepared and alkylated to 1,3-dialkyluracils 2a-d and 2-alkylthiouracils, 3, 4 and 6 , by electrophilic substitution with alkyl halides. Reaction of 1b with dibromoethane and 1,3-dibromopropane gave the corresponding bicyclic products, 7-aryl-6-cyano-2,3-dihydrothiazolo[3,2-a]pyrimidin-5-ones 5a,b and 8-aryl-7-cyano-3,4-dihydro-2H-pyrimido[2,3-b][1,3]thiazin-6-ones 5c-g . Nucleophilic substitution on 6 with hydrazine led to 7 which on refluxing with formic acid gave 5-aryl-6-cyano-8-methyl-s-triazolo[3,4-b]pyrimidin-7-ones ( 9 ), while with acetic and propionic acids only 2-acylhydrazino-3-methyl-4-oxo-5-cyano-6-arylpyrimidines 8a,b were isolated. The hydrazine 7 undergoes cyclization with acetylacetone and methyl dimethylmercaptoacrylate providing 2-(pyrazol-1-yl)-3-methyl-4-oxo-5-cyano-6-substituted pyrimidines 10 , and 11 . Some of the compounds were screened for antibacterial-, antifungal- and antiviral activities and a few of them showed significant chemotherapeutical activities.     

Regioselective Synthesis of the 5,6‐Dihydro‐4H‐furo[2,3‐c]pyrrol‐4‐one Skeleton: A New Class of Compounds

We hereby report the first preparation of the 5,6‐dihydro‐4H‐furo[2,3‐c]pyrrol‐4‐one ( 3 ) and its derivatives starting from methyl 3‐(methoxycarbonyl)furan‐2‐acetate ( 8 ). The ester functionality connected to the methylene group was regiospecifically converted to the desired monohydrazide 9 . Conversion of 9 into the acyl azide 10 followed by Curtius rearrangement gave the corresponding isocyanate derivative 11 (Scheme 2). Reaction of 11 with different nucleophiles produced urethane and urea derivatives (Scheme 3). Intramolecular cyclization reactions provided the target compounds (Scheme 5). Removal of the amine‐protecting group formed the title compound 3 .     

Enantioselective imine Michael reaction for the preparation of the (8′R,8a′S)-8,8a′-dimethyl-1′,3′,4′,7′,8′,8a′-hexahydrospiro[1,3-dioxolane-2,2′(6′H)naphthalen]-6′-one building block. A formal synthesis of (+)-valencenol

The enantioselective Michael addition of a chiral imine of 4-protected 2-methylcyclohexane-1,4-dione to phenyl crotonate led after cyclization to the corresponding bicyclic lactam. Reductive cleavage of the chiral moiety followed by saponification gave the corresponding keto-acid, which was cyclized to afford a lactone. Belleau–Fujimoto reaction of the lactone then led to the title building block (diastereoselectivity 96:4, e.e. >98%) in 11% overall yield from the starting dione. (8R,8aS)-(+)-8,8a-Dimethyl-3,4,6,7,8,8a-hexahydronaphthalen-2(1H)-one was obtained after reduction of the carbonyl group, acetylation, and reductive cleavage–deprotection (52% overall yield), representing a formal synthesis of (+)-valencenol.     

The Composition of Keto Aldoses in Aqueous Solution as Determined by NMR Spectroscopy

Keto aldoses usually form complex mixtures of equilibrating isomers in solution. This is due to the two different positions that may be used for ring closure in dicarbonyl sugars. The composition of various 2‐keto aldoses 1 – 5 and 8 , the 3‐keto aldose 2‐deoxy‐D ‐erythro‐hexos‐3‐ulose ( 9 ), and the ketose 1‐deoxy‐D ‐ribulose ( 10 ) in aqueous solution has been determined by NMR spectroscopy. The investigated keto aldoses form equilibria containing three to fifteen isomers. Among various furanose and pyranose ring structures stemming from 1,4‐, 1,5‐, 2,5‐, and 2,6‐cyclization, bicyclic forms were also found in several cases. The 2‐keto aldoses mainly exist as hydrated isomers in H₂O. Therefore, these forms and their proportions were compared to forms found in two homomorphous aldoses and one homomorphous ketose as model compounds. Besides the NMR data, also the composition of the 2‐keto aldoses agreed with the average of forms found in the model compounds, a finding that might eventually be useful for deducing the composition of other keto aldoses.     

Synthesis of 3-methyl-[1,2,4] -triazepino[6,5,4-jk] carbazol-4(3H)one

The title compound ( 14 ), a representative of a novel ring system, was prepared from 9H-carbazole-1-carboxylic acid 1-methylhydrazide ( 7 ) and triethyl orthoformate. Attempted cyclization of 7 with triethyl orthoacetate led only to 9H-carbazole-l-carboxylic acid 2-(l-ethoxyethylidene)-l-methylhydrazide ( 16 ). Treatment of 16 with trifluoroacetic acid gave 9H-carbazole- 1 -carboxylic acid ( 12 ). A postulated mechanism for this transformation was supported by studies with model compounds. A new synthesis of 1 -benzoyl-2-methylhydrazine ( 24 ), using 1-acetyl-1-methylhydrazine ( 22 ) as a synthon, is described.