Maximum-overlap hybridization in bicyclo [2.1.0] pent-2-ene

Applying the method of maximum overlap, the hybridization in bicyclo[2.1.0]pent-2-ene is determined. In addition, upon comparing these results with those of cyclobutene, cyclopropane, Dewar benzene and bicyclo[1.1.0]butane, it is found that the hybrids calculated by the method of maximum overlap are transferable between parts of molecules for which the structural features are similar.     

The Thermal Isomerizations of Bicyclo[2.1.0]pent-5-yl Methyl Ketones: endo-exo stereomutation and cyclopropyl-allylic rearrangement to cyclopent-2-enyl methyl ketones

Bicyclo[2.1.0]pent-5-yl methyl ketones undergo two thermal isomerization reactions. The endo-exo stereomutation follows the ring-flip path in better than 90%, with inversion of the configuration of the angular carbon atoms by cleavage and reclosure of the central bond. Stereomutation and cyclopropyl-allylic rearrangement to cyclopent-2-enyl methyl ketone do not involve a common intermediate and proceed on separate potential energy surfaces. The activation parameters of the rearrangement suggest an allowed concerted cycloreversion process.     

Preparation of methano[1,3]oxazolo[3,2-a]quinolin-2-ones from 2-(pent-3-en-2-yl)anilines

Acid-catalyzed Claisen aromatic rearrangement of ethyl N-(pent-3-en-2-yl)-N-phenylglycinate leads to the formation of ethyl N-[2-(pent-3-en-2-yl)phenyl]glycinate. The reaction of sodium salt of N-acetyl-2-(pent-3-en-2-yl)-4-methylaniline with methyl bromoacetate afforded ethyl N-acetyl-N-[4-methyl-2-(pent-3-en-2-yl)phenyl]glycinate. The hydrolysis of synthesized esters, the conversion of the obtained acids by treating with ethyl chloroformate into munchnones, and the subsequent [3+2]-cycloaddition provided methoxazoloquinoline structures.     

1-acyl-2-cyclopentenes and 5-acylbicyclo[2.1.0]pentanes: photochemical and thermal isomerizations

The photochemistry of 1-acyl-2-cyclopentenes varies with the nature of the acyl group. On direct irradiation the aldehyde eliminates carbon monoxide in the singlet excited state, and the aroyl compounds cleave to allyl-aroyl radical pairs both from the singlet and triplet states. In competition to α-cleavage the methyl ketones isomerize in an allylic 1,3-acetyl shift. The lowest-lying reactive triplet of these methyl ketones, characterized as a ³(π, π*) state in the case of the 3-phenyl homologue, undergo oxadi-π-methane rearrangement to a mixture of endo- and exo-5-acetylbicyclo[2.1.0]pentanes.The ground state-acetylbicyclopentanes react in two ways at elevated temperatures: endo-exo stereomutation by selective cleavage of the central cyclopropane bond and reclosure of the 1,3-cyclopentane diradical intermediate, and a rearrangement of the endo isomer to 1-acetyl-2-cyclopentenes on a separate potential energy surface involving a formal 1,2-acetyl shift. The unusually large negative entropy of activation for this latter reaction is suggestive of a concerted electrocyclic process in which the electrons of the internal cyclopropane and the C(5)-acetyl bonds participate.     

Synthesis and ring opening reactions of a 2-silabicyclo[2.1.0]pentane

Methyl 2-silabicyclo[2.1.0]pentane-1-carboxylate, obtained by a photochemical intramolecular cyclopropanation reaction of an [small alpha]-allylsilyl-[small alpha]-diazoacetate, undergoes ring opening reactions under different conditions leading to methyl 2-[diisopropyl(methoxy)silylmethyl]cyclopropane-1-carboxylate, a 1-sila-4-cyclopentene-2-carboxylate or an allyl(methoxysilyl)ketene.     

Conjugated polymers featuring heavier main group element multiple bonds: a diphosphene-PPV

A new sterically encumbered bifunctional ligand has been developed, and its ability to provide simultaneous stabilization for two low-coordinate phosphorus centers has allowed the synthesis of new hybrid inorganic-organic conjugated materials. The new phosphaalkene polymers have been prepared from a diphospha-Wittig reagent and are exclusively E-configured about the P=C bonds. An unprecedented polymer having diphosphene (-P=P-) units in the polymer main chain is also reported. The soluble polymers were characterized by UV-visible and fluorescence spectroscopy, as well as by 1H and 31P NMR spectroscopy.     

Bicyclo[2.2.1]hepta-2-ene-5-yl-7-ylium radical cation: a theoretical validation of a bishomoaromatic radical cation intermediate

[structure: see text] A natural bond orbital analysis of the distonic bicyclo[2.2.1]hepta-2-ene-5-yl-7-ylium radical cation interprets its structure and radical character by a three-center two-electron bond between C2, C3, and C7 (a bishomoaromatic stabilization) and a singly occupied orbital on C5, n(5). Moreover, B3LYP/6-311+G(d,p) ESR parameters, which agree excellently with experiment, are interpreted in terms of spin polarization in the natural hybrids of sigma(C5-H5), and a dual hyperconjugative effect involving n(5), sigma(C1-H1a), sigma(C1-H1b), and antibonding counterparts.     

Epoxidation of 2-azabicyclo[2.2.1]hept-5-en-3-one

Epoxidation of 2-azabicyclo[2.2.1]hept-5-en-3-one has been performed in high yield with potassium hydrogen persulfate at pH 6, ¹H nmr data indicate an exo stereoconfiguration of the epoxide.     

Effects of the alkali metal counter ions on the germanium-germanium double bond length in a heavier group 14 element ethenide salt

The first, well-characterized 1,2-dilithium salt of a group 14 element ethenide species, [[(dioxane)(0.5)(Et2O)LiGeC6H3-2,6-Mes2]2]infinity, shows that the positions of the cations have a large effect on the length of the Ge-Ge double bond.     

The Homoconjugated Electron-Releasing Carbonyl Group of 1-Methylbicyclo[2.2.1]hept-5-en-2-one. Regioselective syntheses of 5-chloro- and 6-chloro-1-methylbicyclo[2.2.1]hept-5-en-2-one

Syntheses of (±)-2-exo-cyano-1-methyl-7-oxabicyclo[2.2.1]hept-5-en-2-endo-yl acetate ( 1 ) and of (±)-1-methyl-7-oxabicyclo[2.2.1]hept-5-en-2-one ( 2 ) are reported. The additon of PhSeCl to 1 afforded (±)-5-endo-chloro-2-exo-cyano-1-methyl-6-exo-(phenylselenenyl)-7-oxabicyclo[2.2.1]hept-2-endo-yl acetate ( 6 ), whereas 2 added to PhSeCl with the opposite regioselectivity giving (±)-6-endo-chloro-1-methyl-5-exo-(phenylselenenyl)-7-oxabicyclo[2.2.1]heptan-2-one ( 7 ). These adducts were converted into 5-chloro-1-methyl-7-oxabicyclo[2.2.1]hept-5-en-2-one ( 9 ) and 6-chloro-1-methyl-7-oxabicyclo[2.2.1]hept-5-en-2-one ( 10 ), respectively.     

Photochemical Rearrangements of Chiral Bicyclo[2.2.2]oct-5-en-2-Ones1

Photochemical oxadi-π-methane rearrangement (1,2-acyl shift) of the chiral bicyclo[2.2.2]oct-5-en-2-ones 2 and 3 furnishes the tricyclic ketones 5 and 6 , whereas the 1,3-acyl shift generates the cyclobutanones 7 and 8 respectively.