Photochemical rearrangement of 8-oxabicyclo[3.2.1]oct-6-en-2-ones

Irradiation of 8-oxabicyclo[3.2.1]oct-6-en-2-ones results in a 1,3-acyl rearrangement. The initial photoproduct undergoes a subsequent reaction involving hydrogen transfer followed by intramolecular cycloaddition of a ketene intermediate.     

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).     

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...     

Synthesis of a novel series of tetracyclic opioid antagonists incorporating an 8-aminobicyclo[3.2.1]oct-6-ene sub-unit

The bridged bicyclo[3.2.1]oct-ene and -ane amines 9-13 have been prepared via [3+2]cycloaddition of allylic alcohols 6 to alkynes 7, and assessed as ligands at opioid receptors. Amine 10b is a potent antagonist at μ receptors.     

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.     

Conformations and reactions of bicyclo[3.2.1]oct-6-en-8-ylidene

Bicyclo[3.2.1]oct-6-en-8-ylidene (1) can assume either the conformation of "classical" carbene 1a or that of foiled carbene 1b in which the divalent carbon bends toward the double bond. Oxadiazoline precursors for the generation of 1 were prepared, followed by photochemical and thermal decomposition as well as flash vacuum pyrolysis (FVP) of a tosyl hydrazone sodium salt precursor, to give a number of rearrangement products. Matrix isolation experiments demonstrate the presence of a diazo intermediate and methyl acetate in all photochemical and thermal precursor reactions. The major product from rearrangements of "classical" bridged carbene 1a is bicyclo[3.3.0]octa-1,3-diene as a result of an alkyl shift, while dihydrosemibullvalene formed from a 1,3-C-H insertion. In contrast, thus far unknown strained bicyclo[4.2.0]octa-1,7-diene formed by a vinyl shift in foiled carbene 1b. The experimental results are corroborated by density functional theory (DFT), MP2, and G4 computations.     

8-phosphabicyclo[3.2.1]octanes—II: The synthesis and stereochemistry of 8-phosphabicyclo[3.2.1]oct-6-enes

Several new 8-phosphabicyclo[3.2.1]oct-6-enes and -6-en-3-yl acetates were prepared by the alkyl (or aryl)dihalophosphane addition to cyclohepta -1,3-diene and 1-acetoxy cyclohepta-3,5-diene. The P-configuration in two P-epimer pairs (3, 4 and 5, 6) and three other compounds which were each obtained as a single isomer (1, 2 and 7) was determined by investigation of the NMR spectra, i.e. by complexation of the compounds with Eu(dpm)₃ as well as from the various phosphorus-hydrogen coupling constants. Compounds possessing the same P-substituent were correlated among themselves and in the case of the PPh bearing compounds (1 and 7) further correlation to a known compound (8a) was established. The chemical behaviour of the C₆C₇ double bond is discussed and compared with the corresponding behaviour in trop-6-enes. Great steric hindrance was found for this bond, for which the following sequence is suggested:

The synthesis of a phosphaatropine analog is described.     

Synthesis of 4, 8-dihydroxy-3-methyl-5,6-benzo-2-oxabicyclo[2.2.2]oct-5-ene

The title compound having the same relative configurations as granaticin($\text{1}$) and U-58,431($\text{2}$) was prepared either by dehydrogenative cyclization of the precursor $\text{9a}$ or by pinacol cyclization of the dicarbonyl compound $\text{15}$.     

On the conformation of 8-substituted bicyclo [3.2.1] oct-6-en-3-ones

A series of 8-substituted bicyclo [3.2.1] oct-6-en-3-ones (of type i) possessing various R₁ and R₂ groups were prepared and characterized. The conformations of the possible isomers of 1-4 were assigned according to the following three methods: (a) NMR spectrum, (b) time averaged precise metal ion location within the Eu (dpm)₃-carbonylic compound complex, (c) UV spectra. Comparison of the chair and boat conformers by UV spectra showed that interactions between the double bonds and the carbonyl occurred in both cases, although to different extents, the ε being dependent on R₁ and R₂. The fore-mentioned interaction exists even in both series of the C₆C₇ dihydro derivatives.     

Alkoxide-Accelerated [1,3] Sigmatropic Shift of Bicyclo[3.2.1]oct-6-en-2-ols to 8-endo-Hydroxybicyclo[3.3.0]oct-2-en-4-ones

Bicyclo[3.2.1]oct-6-en-2-ols 6 are shown to undergo [1,3] sigmatropic shift to afford 8-endo-hydroxy-bicyclo[3.3.0]oct-2-en-4-ones 8 under the influence of potassium hydride.     

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.     

Bicyclo[3.2.1]octane and 6-oxabicyclo[3.2.2]nonane type neolignans from Magnolia denudata

From the ethyl acetate soluble fraction of twigs of Magnolia denudata (Magnoliaceae), seven new neolignan derivatives, 1-7, were isolated along with eighteen known lignan and neolignan derivatives, 8-25. The structures of the new neolignans were elucidated by means of spectral methods, especially by 1H-NMR and 13C-NMR spectra, and two dimensional NMR methods such as 1H-detected heteronuculear multiple bond connectivity1 (HMBC), 1H-detected multiple quantum coherence (HMQC) and 1H-1H-correlation spectroscopy (COSY). Compounds 1-4 have novel structures possessing a 6-oxabicyclo[3.2.2]nonane skeleton and compounds 5-8 also have novel structures possessing a bicyclo[3.2.1]octane skeleton. The anti-platelet-activating factor (PAF) activity of these compounds was tested by measurement of inhibition activity against acetyl transferase to lyso-PAF.