Reactions of substituted 8-oxatricyclo[3.2.1.02,4]octan-6-ones and 9-oxatricyclo[3.3.1.02,4]nonan-6-ones with methylmagnesium bromide and lithium aluminum hydride

Substituted 8-oxatricyclo[3.2.1.0^2,4]octan-6-one and 9-oxatricyclo[3.3.1.0^2,4]-nonan-6-one obtained by treating substituted cyclopropenes with carbonyl ylides in reactions with methylmagnesium bromide and lithium aluminum hydride were stereoselectively converted into the corresponding alcohols.     

Stereoselective carbonyl reductions of chloro-substituted 8-oxabicyclo[3.2.1]oct-6-en-3-ones

The lithium aluminium hydride reduction of 2,2,4,4-tetrachloro-8-oxabicyclo[3.2.1]oct-6-en-3-one (8) was reinvestigated. In contrast to most halogeno-substituted oxabicyclic ketones, which give predominantly the corresponding endo alcohols, the expected (3endo)-2,2,4,4-tetrachloro-8-oxabicyclo[3.2.1]oct-6-en-3-ol (9n) is formed in a minute proportion. An X-ray structure analysis of the dominating product gave proof of the exo-alcohol, i.e., (3exo)-2,2,4,4-tetrachloro-8-oxabicyclo[3.2.1]oct-6-en-3-ol (9x). On the other hand, reduction of trichloroketone 11, 2,2,endo-4-trichloro-8-oxabicyclo[3.2.1]oct-6-en-3-one, and the methoxy-substituted chloroketones 13 and 14 provided the corresponding endo alcohols (12 and 15).     

Conformational study of N-substituted 8-azabicyclo[3.2.1]octan-3-ones

N-Substituted 8-azabicyclo[3.2.1]octan-3-ones have been studied by ¹H and ¹³C NMR spectroscopy. In CDCl₃ solutions, these ketones display the same preferred conformation. The pyrrolidine and piperidone rings adopt a flattened N-8 envelope and distorted chair conformation, puckered at N-8 and flattened at C-3, respectively, with the N-substituent in axial position with respect to the piperidone ring.     

Allylsilane-interrupted homo-Nazarov cyclization and synthesis of bicyclo[3.2.1]octan-8-ones

The combination of homo-Nazarov cyclization of 2-(tert-butyldiphenylsilylmethyl)cyclopropyl vinyl ketone leading to oxyallyl cation and its subsequent [3+2] capture by allylsilane has been demonstrated as an useful strategy for the construction of functionalized bicyclo[3.2.1]octan-8-ones. The [3+2] capture proceeds exclusively in the exo mode to make the overall reaction diastereoselective. The less substituted end of the oxyallyl cation was found to react nearly two times faster than the more substituted end.     

Synthesis of 2,7-Diazabicyclo[3.2.1]oct-3-ene Derivatives

Russian Journal of Organic Chemistry - Tetracyanoethylene adducts with ketones, 4-oxoalkane-1,1,2,2-tetracarbonitriles reacted with hydrogen chloride or phosphorus(III) chloride in 1,4-dioxane to...     

C1-C2 cleavage of C1-functionalized 8-oxabicyclo-[3.2.1]-oct-6-en-3-one. Stereoselective preparation of 4-substituted butenolides

Diastereoisomeric epimers at C1′ of 4-(1-methyl-2-oxo-butyl)-2-butenolide, and the corresponding saturated γ-lactones, were synthesized by hydrolysis of 1-methoxy-8-oxabicyclo[3.2.1] oct-6-en-3-one, under acidic conditions. These butenolides are interesting synthetic building blocks, precursors of biologically active natural products like insect pheromones. Their formation could be explained by a cleavage at the C1-C2 bond of the oxabicyclic precursor. On the basis of the experimental data we have proposed a mechanism of hydrolytic cleavage which is formally an intramolecular reverse Dieckmann process.     

Green Nano-Silica Sulfuric Acid-Catalyzed Synthesis of New 6-Amino-8-aryl-7-(benzenesulfonyl)-2-(hydroxymethyl)-pyrano[3,2-b]pyran-4(8H)-one Derivatives

Russian Journal of Organic Chemistry - Some new 6-amino-8-aryl-7-(benzenesulfonyl)-2-(hydroxymethyl)pyrano[3,2-b]pyran-4(8H)-ones have been synthesized in improved yields by one-pot three-component...     

Synthesis of the 5-hydroxymethyl-6-aryl-8-oxabicyclo[3.2.1]oct-3-en-2-one natural products descurainin and cartorimine

Reaction of pyranulose 6 with styrenes 12c or 13 and Et₃N in CH₂Cl₂ at 25 °C afforded the [5+2] cycloadducts 14c and 15, which were hydrolyzed to give the natural products 1 and descurainin (2) in 24 and 27% overall yield, respectively. Heating pyranulose 6 with cinnamate ester 21 in the presence of 2,6-di-t-butylpyridine in CH₃CN at 175 °C afforded the [5+2] cycloadduct, which was hydrolyzed to give cartorimine (3) in 13% yield.     

Synthesis and reactions of 2-aryl-8-oxabicycloc[3.2.1]oct-6-en-3-ones

A number of 1-aryl-1-bromopropanones have been prepared and converted into the corresponding oxyallyl carbocations. These were reacted with furan to produce the expected 2-aryl-8-oxabioyclo[3.2.1]oct-6-en-3-ones, as well as a number of interesting side-products. These included 3-aryl-propanoic acid esters produced via Favorskii rearrangements. Attempts to cleave the ether linkage in the cycloadducts using bromotrimethylsilane produced instead 1-aryl-3-furylpropanones in excellent yield.     

Enantioselective synthesis of bicylco[3.2.1]octan-8-ones using a tandem Michael-Henry reaction

Bicyclo[3.2.1]octan-8-ones have been prepared from a tandem Michael-Henry reaction between cyclohexane-1,2-diones and nitroalkenes using a quinine-derived thiourea as the catalyst. Although four stereogenic centers were created during the reaction, only two diastereomers were obtained in good diastereoselectivity and high enantioselectivity (92-99% ee). When 3-methylcyclohexane-1,2-dione (R¹=Me) was used as the substrate, only the regioisomeric product of the corresponding thermodynamic enolate was obtained.     

3-氨基-6/8取代-1H-吡唑[4,3-c]喹啉类化合物的合成

研究了合成3-氨基-6/8取代-1H-吡唑[4,3-c]喹啉类化合物的简易方法.通过3-芳基-4-氨基-5-巯基-1,2,4-三唑与6-/8-取代-4-羟基喹啉羧酸在三氯氧磷催化下的缩合反应及所生成的3-芳基-6-(6-/8-取代-4-氯喹啉-3-基)-1,2,4-三唑[3,4-b]-1,3,4-噻二唑类化合物与水合肼在乙醇中的肼解反应,合成了6个3-氨基-6/8取代-1H-吡唑[4,3-c]喹啉类化合物,并对活泼的氨基进行了初步研究,新化合物通过元素分析,IR,¹HNMR和MS确定结构,并讨论了其波谱性质.     

Construction of 2,3- and 3,4-Functionalized Silacyclopentanes: Synthesis of 6-Aza-2,2-Diphenyl-2-Silabicyclo[3.1.0]Hexane and 6-Aza-3,3-Diphenyl-3-Silabicyclo[3.1.0]Hexane Derivatives

The synthesis of five azasilabicyclo[3.1.0]hexanes containing an aziridine function in the α- or the β- position of the silicon atom is described. These bicyclic heterocompounds differ by the various substituents (H, Me, CO₂Et, CPh₃) on the nitrogen atom.