Synthesis and structural revision of naturally occurring ayapin derivatives

The synthesis of three highly oxygenated naturally occurring coumarins, 8-methoxy-6,7-methylenedioxycoumarin, 5-methoxy-6,7-methylenedioxycoumarin and 5,8-dimethoxy-6,7-methylenedioxycoumarin is described for the first time, together with a new method for the preparation of ayapin (6,7-methylenedioxycoumarin). Comparison of the spectroscopic data of the synthetic tetraoxygenated coumarin 5,8-dimethoxy-6,7-methylenedioxycoumarin with literature reports resulted in the structural revision of several natural coumarins. Two coumarins, both identified as 5,8-dimethoxy-6,7-methylenedioxycoumarin must have other structures, while the structure of another coumarin, described as the isomeric 7,8-dimethoxy-5,6-methylenedioxycoumarin has to be revised to 5,8-dimethoxy-6,7-methylenedioxycoumarin.     

The structure of covalent hydrates of alloxazines. A reinvestigation

It is shown by ¹³C-NMR. and synthesis of 6,7-dimethyl-3-ethoxycarbonylamino-quinoxaline-2-carboxamide ( 5 ) and methyl 6,7-dimethyl-3-(N′-methylureido)-quinoxaline-2-carboxylate ( 6 ) that hydrolysis of lumichrome ( 1 , R = H) must yield 6,7-dimethyl-3-ureidoquinoxaline-2-carboxylic acid ( 2 , R = H) and not 6,7-dimethyl-2-oxo-1,2,9,9a-tetrahydrooxazolo[4,5-b]quinoxaline-9a-carboxamide ( 2a , R = H), as previously proposed.     

Cinnoline chemistry. XIV. 3-cyclohexylcinnolines

The synthesis of 3-cyclohexyl-6,7-dimethoxy-1H-4-cinnolone ( 4 ), 4-chloro-3-cyclohexyl-6,7-dimethoxycinnoline ( 5 ) and 8-bromo-3-cyclohexyl-6,7-dimethoxy-1H-4-cinnolone ( 6 ) are reported.     

[3+2] Cyclopentane annulation reactions using organoiron reagents. Hydroazulene synthesis.

A one step synthesis of 4-ketohydroazuleneiron complexes 6,7 and 8 from troponeiron tricarbonyl is described.     

Facile and efficient synthesis of 1-[2-(6,7-dimethyl-3,4-dihydronaphthalen-2-yl)ethyl]pyrrolidine hydrochloride

An efficient and facile procedure for the preparation of 1-[2-(6,7-dimethyl-3,4-dihydronaphthalen-2-yl)ethyl]pyrrolidine hydrochloride from 6,7-dimethyl-1,2,3,4-tetrahydronaphtalen-1-one in four steps is proposed. It includes one-step synthesis of 1-(6,7-dimethyl-1,2,3,4-tetrahydronaphthalen-2-yl)acetic acid as key intermediate and subsequent transformations of functional groups therein. Published in Russian in Zhurnal Organicheskoi Khimii, 2008, Vol. 44, No. 3, pp. 449–453. The text was submitted by the authors in English.     

Oxa-Pictet-Spengler reaction in water. Synthesis of some (±)-1-aryl-6,7-dimethoxyisochromans

An acid catalyzed oxa-Pictet-Spengler reaction ‘on water’ leading to the synthesis of a variety of 1-aryl-6,7-dimethoxyisochromans is described. The aqueous chemistry is a much cleaner, efficient, cheaper and simple method for synthesis. The scope of reactions was extended to thia-Pictet-Spengler reaction to afford the some isothiochromans.     

Total synthesis of (-)- and ent-(+)-vindoline and related alkaloids

A concise 11-step total synthesis of (-)- and ent-(+)-vindoline (3) is detailed based on a unique tandem intramolecular [4 + 2]/[3 + 2] cycloaddition cascade of a 1,3,4-oxadiazole inspired by the natural product structure, in which three rings and four C-C bonds are formed central to the characteristic pentacyclic ring system setting all six stereocenters and introducing essentially all the functionality found in the natural product in a single step. As key elements of the scope and stereochemical features of the reaction were defined, a series of related natural products of increasing complexity were prepared by total synthesis including both enantiomers of minovine (4), 4-desacetoxy-6,7-dihydrovindorosine (5), 4-desacetoxyvindorosine (6), and vindorosine (7) as well as N-methylaspidospermidine (11). Subsequent extensions of the approach provided both enantiomers of 6,7-dihydrovindoline (8), 4-desacetoxyvindoline (9), and 4-desacetoxy-6,7-dihydrovindoline (10).     

Synthesis of tylophorine

A biogenetic type of synthesis of tylorphorine 12 (3.8% yield, established by a radio-dilution method) was achieved by ferricyanide oxidation of 6,7-di(3-hydroxy-4-methoxyphenyl)-6,7-dehydroindolizidine 10.     

Novel stereocontrolled approach to syn- and anti-oxepene-cyclogeranyl trans-fused polycyclic systems: asymmetric total synthesis of (-)-Aplysistatin, (+)-Palisadin A, (+)-Palisadin B, (+)-12-hydroxy-palisadin B, and the AB ring system of adociasulfate-2 and toxicol A

A new stereocontrolled method for the formation of trans-anti cyclogeranyl-oxepene systems is described. The demanding stereochemistry is secured by stereoselective coupling of a cyclogeranyl tertiary alcohol with a 1,2-unsymmetrically substituted epoxide, while the formation of the highly strained oxepene is achieved employing ring-closing metathesis. Since the stereochemistry of the trans-fused 6,7-ring system is determined by the epoxide, the method also allows the construction of trans-syn 6,7-ring systems. This approach leads to the synthesis of the AB fragment of Adociasulfate-2 and Toxicol A, for the first time. The flexibility and efficiency of the presented strategy is demonstrated by the total asymmetric synthesis of (-)-Aplysistatin, (+)-Palisadin A, (+)-12-hydroxy-Palisadin B, and (+)-Palisadin B, employing two similar key intermediates.     

Polycyclic N-heterocyclic compounds. XLV. Synthesis of 4-substituted 5,6-dihydrobenzo[h]quinazolines and 6,7-dihydro-5H-benzo[6,7]cyclohepta[1,2-d]pyrimidines and their inhibitory activity on platelet aggregation

The synthesis of 4-substituted 5,6-dihydrobenzo[h]quinazolines and 6,7-dihydro-5H-benzo[6,7]cyclohepta-[1,2-d]pyrimidines with substituents which are an electron-attracting group such as a nitrite, an amide, a thione, or a carboxyl group is described. Their inhibitory activity against collagen-induced platelet aggregation was also investigated.     

Heterocyclic analogs of pleiadiene. 58. Thiocyanogenation of permidones. Synthesis of perimidone-6,7-disulfides

The thiocyanogenation of 1, 3-disubstituted perimidones gives good yields of their 6 (7)-monothiocyano and 6, 7-dithiocyano derivatives. Alkaline hydrolysis of these derivatives leads to the formation of the corresponding disulfides. The reduction of 1, 3-dimethylperimidone-6,7-disulfide is accompanied by the destruction of the disulfide bridge and may be used for the synthesis of 6,7-dialkylmercaptoperimidones.Communication 57, see ref. [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1493–1496, November, 1985.     

Synthesis of fluorinated 1,8-naphthyridinone derivatives

Processes for the synthesis of fluorinated 1,8-naphthyridinone derivatives including 6,7-difluoro-1,8-naphthyridin-2-one are described.     

Polyhydroxylated nortropanes starting from D-glucose: Synthesis of homochiral (+) and (−)-calystegines B2

The cycloheptano-isoxazoline 1, prepared from D-glucose, is converted to 6,7-dideoxy cycloheptitols which are suitable precursors for the synthesis of enantiomerically pure (+) and (−)-Calystegines B₂.     

Novel polymers of intrinsic microporosity (PIMs) derived from 1,1-spiro-bis(1,2,3,4-tetrahydronaphthalene)-based monomers

The synthesis of novel monomers based upon the rigid 1,1′-spiro-bis(1,2,4,5-tetrahydro-6,7-dihydroxynaphthalene) framework is reported. These monomers can be used for the synthesis of polymers of intrinsic microporosity (PIMs) due to their reactive catechol units and nonlinear shape, which introduces the necessary sites of contortion into the resulting PIM.     

New Aryl Derivatives of Quinolinedione and Related Heterocyclic Compounds

The synthesis of new derivatives of 6,7‐dibromoquinoline‐5,8‐dione and 6,7‐dichloroquinoline‐5,8‐dione via palladium/Sphos‐mediated Suzuki–Miyaura cross‐coupling reaction is reported. The 6,7‐dibromoquinoline‐5,8‐dione and 6,7‐dichloroquinoline‐5,8‐dione intermediates were prepared in a three‐step reaction from 8‐hydroxyquinoline. The palladium‐catalyzed reactions of 6,7‐dibromoquinoline‐5,8‐dione and 6,7‐dichloroquinoline‐5,8‐dione with a variety of aryl boronic acids provide coupled compounds in high yields. The arylation of 6,7‐dibromoquinoline‐5,8‐dione and 6,7‐dichloroquinoline‐5,8‐dione with 4‐bromophenyl boronic acid supplied 6,6′‐(1,4‐phenylene)bis(7‐bromoquinoline‐5,8‐dione) and (4‐(6‐(4‐(6‐chloro‐5,8‐dihydroquinolin‐7‐yl)phenyl)‐5,8‐dihydroquinolin‐7‐yl)phenyl)boronic acid respectively, in addition to the expected coupled compounds in moderate yields. Also, Pd(0)/PPh₃ allowed the 7‐chloro‐6‐(4‐nitrophenyl)quinoline‐5,8‐dione and 7‐chloro‐6‐phenylquinoline‐5,8‐dione to be synthesized via Heck reaction. The yields of the synthesized target molecules depend largely on the reaction conditions and the type of ligands employed. Structural assignments of the synthesized compounds were established by spectra and analytical data.     

Chemistry of naphthazarin derivatives: XV. Bromination of naphthazarin and its derivatives

Bromination of a number of naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) derivatives having different substituents in the aromatic ring with molecular bromine in carbon tetrachloride was studied. Preparative procedures for the synthesis of 2-bromo-5,8-dihydroxy-7-methoxy-1,4-naphthoquinone, 2-bromo-6,7-dichloro-5,8-dihydroxy-1,4-naphthoquinone, 2-bromo-3,5,8-trihydroxy-1,4-naphthoquinone, and 2-bromo-6,7-dichloro-3,5,8-trihydroxy-1,4-naphthoquinone were developed.     

Vicinal diester dianions. Annelation with allylic and benzylic αω-dihalides. Synthesis of tricyclobuta[1,2:3,4:6,7]naphthalene

A new method of annelation utilizing the reaction of vicinal diester dianions with allylic and benzylic α,ω-dihalidesis described. The synthesis of tricyclobuta-[1,2:3,4:6,7] naphthalene is reported.     

New Approach to Synthesis of 6,7—Dimethoxyisatin

A new approach to synthesis of 6,7-dimethoxyisatin is reported.2-nitro-3,4-dimethoxy mandelonitrile in glacial acetic acid was treated with the solution of stannous chloride in hydrochloric acid to give 6,7-dimethoxyisatin in a high yield.     

A simple route to 6- and 7-fluoro-substituted naphthalene-1-carboxylic acids

A simple one-pot method for the synthesis of 6-fluoro- and 6,7-difluoro-1-naphthoic acid is described. 6-Fluoro-1-naphthoic acid can be converted into 7-fluoro-1-naphthoic acid in three straightforward steps.     

An efficient synthesis of substituted anthraquinones and naphthoquinones

An efficient synthesis of 6,7-disubstituted naphthoquinones and 2,3,6,7-tetrasubstituted anthraquinones were developed using the reaction of thiophene dioxides and benzoquinone and naphthoquinone derivatives, respectively.