The Synthesis and Cycloaddition Reactions of 3-Azabicyclo[3.1.0]hex-2-ene 3-oxide and 3-Azabicyclo[3.2.0]hept-2-ene 3-oxide. Highly Strained Bicyclic Nitrones

The synthesis of two strained bicyclic nitrones is described. Subsequent cycloadditions demonstrated a high degree of regiochemical and stereochemical control.     

Crystal structure of 1,1,3,3,8,8-hexachloro-2-oxa-1,3,8-trisilabicyclo[3.3.1]oct-5-ene

Journal of Structural Chemistry -     

Novel 2-phosphabicyclo[2.2.2]oct-5-ene derivatives and their use in phosphinylations

The [4 + 2] cycloaddition of the double-bond isomers ( A and B ) of dihydrophosphinine oxide 1 afforded novel phosphabicyclo[2.2.2]oct-5-ene derivates ( 2–4 ), formation of which was justified by PM3 semiempirical calculations. The compounds of dimer type ( 2–4 ) were utilized in the UV light-mediated fragmentation-related phosphinylation of nucleophiles, especially in that of alcohols. To explore the role of structural modifications on the fragmentation ability, disulfide 5 , phosphabicyclooctane 7 obtained by the hydrogenation of 2 , and the adduct of dihydrophosphinine oxide 1 with benzoquinone ( 7 ) were also synthesized and tested in fragmentation. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:97–106, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10221     

The average structures of 2,3-diazabicyclo[2.2.1]hept-2-ene and 2,3-diazabicyclo[2.2.2]oct-2-ene

The average molecular structures of 2,3-diazabicyclo[2.2.1]hept-2-ene and 2,3-diazabicyclo[2.2.2] oct-2-ene have been determined by electron diffraction in the gas phase. The structural parameters were obtained by applying a least squares analysis on the molecular scattering intensity functions. For 2,3-diazabicyclo[2.2.1]hept-2-ene, C_s symmetry was assumed in calculating the geometry of the molecule. The parameters thus determined are: N₃=N₂ = 1.221 Å, N₃- C₄ = 1.445 Å, C₄-C₅ = 1.538 Å, C-H_(ave.) = 1.112 Å, < C₁N₂N₃ = 116.3°, < N₃C₄C₅ = 105.2°, < C₁C₄C₅ = 71.5°, C₄-C₇ = 1.547 Å, C₅-C₆ = 1.530 Å, < C₁C₇C₄ = 108.0°. For 2,3-diazabicyclo[2.2.2]oct-2-ene, C_2vsymmetry was assumed. The geometrical parameters are: N₃ = N₂ = 1.243 Å, N₃-C₄ = 1.473 Å, C₄-C₅ = 1.550 Å, C₅-C₆ = 1.516 Å, C-H_(ave.) = 1.119 Å,< C₁N₂N₃ = 115.1°, < N₃C₄C₅ = 109.1°, < C₆C₁C₄ = 71.6°.     

The Non-planarity of the Bicyclo[2.2.1]hept-2-ene Double bond. Crystal Structures of Bicyclo[2.2.2]oct-2-ene,Bicyclo[2.2.1]hept-2-ene,and Bicyclo[2.1.1]hex-2-ene Systems

The crystal structures of (1R,4R,5S,8S)-9,10-dimethylidentricyclo[6.2.1.0^2,7]undec2(7)-ene-4,5-dicarboxylic anhydride ( 3 ), (1R,4R,5S,8S)11-isopropylidene-9,10-dimethylidenetricyclo[6.2.1.m^2,7]undec-2(7)-ene-4,5-dicarboxylic anhydride ( 6 ), (1R,4R,5S8S)-9,10-dimethylidenetricyclo[6.2.2.0^2,7]dodec-2(7)-ene-4,5-dicarboxylic anhydride ( 9 ), (1R4R5S8S)-TRICYCLO[6.2.2.0^2,7]dodeca-2(7), 9-diene-4,5-dicarboxylic anhydride ( 12 ) and (4R,5S)-tricyclo[6.1.1.0^2.7]dec-2(7)-ene-4,5-dicarboxylic acid ( 16 ) were established by X-ray diffraction. The alkyl substituents onto the endocyclic bicyclo[2.2.1]hept-2-ene double bond deviate from the C(1), C(2), C(3), C(4), plane by 13.5°4 in 3 and by 13.9° in 6 , leaning toward the endo-face. No such out-of-plane deformations were observed with the bicyclo[2.2.2]oct-2-ene derivatives 9 and 12 . The exocyclic s-cis-butadiene moieties in 3, 6 and 9 do not deviate significantly from planarity. The deviation from planarity of the double bond n bicyclo[2.2.1]hept-2-ene derivatives and planarity in bicyclo[2.2.2]oct-2-ene analogues is shown to be general by analysis of all known structures in the Cambridge Crystallographic Data File. The non-planarity of the bicyclo[2.2.1]hept-2-ene double bond cannot be attributed only to bond-angle deformations which would favour rehybridizatoin of the olefinic C-atoms since the double bond in the more strained bicyclo[2.1.1]hex-2-ene drivative 16 deviates from planarity by less than 4°.     

Metathesis polymer based on 5-trimethylsilylbicyclo[2.2.2]oct-2-ene: Synthesis and gas-transport properties

A new silicon-containing bicyclic monomer 5-trimethylsilylbicyclo[2.2.2]oct-2-ene has been synthesized, and its metathesis polymerization and gas transport properties of the polymer based on it have been studied. The monomer is synthesized by the two-step scheme using the Diels–Alder reaction from 1,3-cyclohexadiene and vinyltrichlorosilane followed by methylation with a Grignard reagent. The resulting 5-trimethylsilylbicyclo[ 2.2.2]oct-2-ene is inactive in metathesis homopolymerization in the presence of first- and second- generation Grubbs catalysts and a Hoveyda–Grubbs catalyst, but it slowly polymerizes when norbornene is present in the reaction mixture. The high-molecular-mass copolymer (M _w = 3.0 × 10⁵, M _w/M _n = 2.8) of 5-trimethylsilylbicyclo[2.2.2]oct-2-ene and norbornene possesses good film-forming properties, and its glass transition temperature is 126°C. The gas-transport properties of the copolymer have been studied.     

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 $\text{15}$.     

Selective fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene by nucleotides

[reaction: see text] The fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by nucleotides has been studied. The quenching mechanism was analyzed on the basis of deuterium isotope effects, tendencies for exciplex formation, and the quenching efficiency in the presence of a molecular container (cucurbit[7]uril). Exciplex-induced quenching appears to prevail for adenosine, cytidine, and uridine, while hydrogen abstraction becomes competitive for thymidine and guanosine. Compared to other fluorescent probes, DBO responds very selectively to the type of nucleotide.     

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...     

Regioselective electrophilic additions to 2-alkoxy- and 2-alkoxymethyl-7-oxabicyclo [2.2.1] hept-5-ene derivatives

The influence of the stereochemistry at C-2 on the selectivity of the reaction between PhSeBr and 2-alkoxymethyl substituted oxanorbornenes has been studied. All endo isomers displayed complete regio- and stereocontrol with incorporation of the electrophile on C-5.     

Theoretical study on the photolysis mechanism of 2,3-diazabicyclo[2.2.2]oct-2-ene

A CASPT2/CASSCF study has been carried out to investigate the mechanism of the photolysis of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) under direct and triplet-sensitized irradiation. By exploring the detailed potential energy surfaces including intermediates, transition states, conical intersections, and singlet/triplet crossing points, for the first excited singlet (S(1)) and the low-lying triplet states (T(1), T(2), and T(3)), we provide satisfactory explanations of many experimental findings associated with the photophysical and photochemical processes of DBO. A key finding of this work is the existence of a significantly twisted S(1) minimum, which can satisfactorily explain the envelope of the broad emission band of DBO. It is demonstrated that the S(1) (n-pi*) intermediate can decay to the T(1) (n-pi*) state by undergoing intersystem crossing (rather inefficient) to the T(2) (pi-pi*) state followed by internal conversion to the T(1) state. The high fluorescence yield and the extraordinarily long lifetime of the singlet excited DBO are due to the presence of relatively high barriers, both for intersystem crossing and for C-N cleavage. The short lifetime of the triplet DBO is caused by fast radiationless decay to the ground state.     

A highly regio- and stereoselective formation of bicyclo[4.2.0]oct-5-ene derivatives through thermal intramolecular [2 + 2] cycloaddition of allenes

Thermal [2 + 2] cycloaddition of allenes with an additional multiple bond is described. By simply heating the allenenes or allenynes having a three-atom tether in an appropriate solvent such as dioxane or DMF, the distal double bond of the allenic moiety regioselectively participates in the cycloaddition to form bicyclo[4.2.0]oct-5-ene derivatives in good to excellent yields. In all the reactions of allenenes, the olefin geometry was completely transferred to the cycloadducts. While the reaction of terminal allenes afforded bicyclic cyclobutane derivatives as a single isomer, the cycloaddition of some internal allenes with axial chirality yielded a diastereomeric mixture of cycloadducts. These results are in good accordance with the stepwise mechanism through a biradical intermediate with a coplanar allyl radical.     

Reactions of dispiro[2.0.2.2]oct-7-ene. Electrophilic and free radical additions

Dispiro[2.0.2.2]oct-7-ene 1 was synthesized by debrominatioa of cis- and trans-7,8-dibromodispiro[2.0.2.2]octane 3a with LAH and by dechlorination of cis- and trans-7,8-dichlorodispiro[2.0.2.2]octane 3b with magnesium. Stepwise electrophilic additions to 1 of HBr, HI, Br₂ and Cl₂ were studied. The major products (and yields) from these reactions were: 7-bromodispiro[2.0.2.2]octane 2a (43%), 4-iodo-4,5-ethanospiro[2,3]hexane 4b (ca. 50%); trans-3a (40%); and cis-3b (20%). Free-radical addition of hydrogen bromide to 1 gave an 80% yield of 7-bromodispiro[2.0.2.2]octane 2a. At ?10°, hydroboration-oxidation of 1 was found to give mainly 7-hydroxydispiro[2.0.2.2]octane 2a in ca. 90% yield; at 25°, near equal amounts of 2c and 4-(2-hydroxyethyl) spiro[2.3]hex-4-ene 14 were obtained.     

Absolute Configuration of 2-Substituted 2-Azabicyclo[2.2.1]hept-5-enes

The diastereoisomeric 2-substituted 2-azabicyclo[2.2.1]hept-5-enes 2 – 4 were prepared by aza-Diels-Alder reaction of cyclopentadiene with the corresponding methaniminium ions. Their relative configurations were deduced using ¹H, ¹H-ROESY experiments, and their absolute configurations were assigned from the crystal structure of the aziridinium derivative (?)- 5 . The absolute configuration of (+)- 1 , i.e. (1R), was assigned by CD spectroscopy.     

Synthesis and crystal structure of 5-amino-4,6-dicyano-3-dicyanomethylene-1, 8,8-trimethyl-2-azabicyclo[2.2.2]oct-5-ene

5-Amino-4,6-dicyano-3-dicyanomethylene-1,8,8-trimethyl-2-azabicyclo[2.2.2]oct-5-ene has been synthesized. The molecular and crystal structure of this compound has been determined.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 169–172, January, 1996.