A study of periselectivity in the thermal cyclisation reactions of diene-conjugated diazo compounds: 1,7-cyclisation as a route to 3H-1,2-diazepines and 1,5-cyclisation leading to new rearrangement reactions of 3H-pyrazoles

A range of diene-conjugated diazo compounds has been generated by the thermal decomposition of the sodium salts of the tosylhydrazones of 1-acyl-1, 3-dienes. Those of type (21) with a $\text{cis}$ relationship of the diazo group and the γ, δ-double bond $\text{and}$ having a $\text{cis}$ hydrogen atom at the diene terminus cyclised only by 1,7 ring closure to give 3$\text{H}$-1,2-diazepines (23). This mode of cyclisation was inhibited by the presence of $\text{cis}$ methyl or phenyl groups at the diene terminus eg in (45). Compounds of this type cyclised by the alternative 1,5- ring closure to give 3-alkenyl-3$\text{H}$-pyrazoles eg (46) as primary products. These observations are explained on the basis of a helical transition state (54) for the 8π electron 1,7-electrocyclisation reaction. Diene-conjugated diazo compounds with a $\text{trans}$ γ,δ double bond eg (32) also cyclised predominantly by 1,5-electrocyclisation to give 3-alkenyl-3$\text{H}$-pyrazoles eg (33). In most cases the 3$\text{H}$-pyrazoles rearranged under the reaction conditions $\text{via}$ alkenyl group and hydrogen migrations to give 1$\text{H}$-pyrazoles eg (34) and (37).     

The regiochemistry of intramolecular n-alkenylnitrone additions: preparative and mechanistic implications

The opposite regiochemistry, observed for the reactions $\text{7a}$ → $\text{8a}$ and $\text{7d}$ → $\text{8d}$, as compared with additions $\text{7b}$ → $\text{9b}$, $\text{7c}$ → $\text{9c}$ and $\text{7e}$ → $\text{9e}$, supports the hypothesis that in the transition state of nitrone-olefin additions the new C,C bond is more advanced than the C,0, bond. Further examples show the superimposition of substituent effects on this intramolecular control.     

Biomimetic chemistry of xylomollin

Kingiside aglucon ($\text{2}$$\text{b}$) undergoes stereoselective addition of CH₃OH to its C(3,4) enol ether double bond to give a C(1,3,9) diastereomer of xylomollin ($\text{1}$), a secoiridoid aglucon that has insect antifeedant properties.     

Flash vacuum thermolysis of spirocyclohexadienones

In an attempt to prepare short-bridged hydroxymetacyclophanes $\text{1b-d}$, the spirocyclohexadienones $\text{2b-d}$ were pyrolyzed by flash vacuum thermolysis (FVT). Instead of $\text{1b-d}$, variable amounts of 4-(5-hexenyl)phenol ($\text{4b}$), β-hydroxybenzocycloalkenes ($\text{5b-d}$) and 4-(trans-1-alkenyl) phenols ($\text{6c-d}$) were obtained. The formation of these products is explained by invoking cleavage of a spiro bond in $\text{2}$ under formation of the intermediate diradical $\text{3}$ which, depending on the length of the aliphatic chain and on the temperature, has several pathways open for isomerization to spin-paired products.     

Reaction of superoxo Co(III) complexes with 2,6-di-t-butyl-p-benzoquinone methides

Superoxo Co(III) complexes derived from Co(Salpr) and [Co(CN)₅]^3? reacted with 2,6-di-$\text{t}$-butyl-$\text{p}$-benzoquinone methides to give 2,6-di-$\text{t}$-butyl-$\text{p}$-benzoquinone and 2,6-di-$\text{t}$-butyl-2,5-cyclohexadienonespirooxiranes as the main products, which are considered to result from nucleophilic attack by the superoxo species on the exo double bond of the quinone methides.     

CC bond formation from schiff base and vinyloxyborane: Synthesis of β-amino acid derivatives

An efficient methodology for the preparation of β-amino acid derivatives ($\text{3}$) by CC bond formation from Schiff bases ($\text{1}$) and vinyloxyborane ($\text{2}$) and their utilization in the synthesis of the pyrimidine moiety ($\text{3f}$) of bleomycin are described.     

Pathways for migration and cleavage of the S-peptide unit of the leukotrienes

Sulfoxides of leukotriene C ($\text{2}$) and various analogs ($\text{5}$, $\text{8}$) undergo a 1,7-migration of sulfur (forming diastereomers $\text{3}$, $\text{6}$, and $\text{9}$, respectively) with noteworthy facility. Generation of the S-halo derivatives of leukotriene C in water results in heterolysis of the CS bond to give (5S, 12R)- and (5S, 12S)-6-$\text{trans}$-leukotriene B in a process which mimics biochemical deactivation.     

The mechanism of [1,3] o to n acyl migrations : A mndo scf-mo study

MNDO SCF-MO calculations suggest that the uncatalysed rearrangements of 0-acyl imidates ($\text{1}$) to the corresponding imides ($\text{2}$) are concerted reactions involving synchronous C-N bond formation and C-O bond cleavage. The calculated dipole moment and atomic charges in the transition state are consistent with the properties of these reactions in solution. The transition states for [1,3] acyl migrations in compounds such as $\text{3}$ which have no lone pair of electrons are predicted to have significantly different properties.     

Benzannelated annulenes -12. : Theoretical study of geometries and 1H chemical shifts of benzannelated [14] annulenes

The geometries and the ¹H chemical shifts of dihydropyrene $\text{1}$ and its benzannelated derivatives $\text{2}$–$\text{8}$ have been studied by means of semiempirical quantum chemical procedures. The calculated bond lengths of $\text{1}$ and proton shifts of $\text{1}$ – $\text{5}$ are in good accord with the corresponding experimental values. We show that monobenzannelation in $\text{2}$ – $\text{4}$ causes considerable bond length alternation in the [14] perimeter and hence reduced diatropocity. The same is true for the phenanth-fused dibenzannelated compounds $\text{4}$ and $\text{7}$. On the other hand we report evidence that anth-fused dibenzannelated dihydropyrenes $\text{5}$, $\text{6}$, and $\text{8}$ should be characterized by symmetric geometrical structures without significant bond length alternation thus leading to enhanced diatropicity.     

Facile synthesis of unsymmetrical benzotetrathiafulvalenes via cleavage of the corresponding hexathioorthooxalates

Unsymmetrical hexathioorthooxalates of types ($\text{1}$) and ($\text{2}$) undergo elimination of dialkyl disulfide on heating in an organic solvent; the reaction, which is catalyzed by acid, proceeds without fission of the central C:C bond and provides the first general, high yield synthesis of unsymmetrical benzotetrathiafulvalenes of types ($\text{3}$) and ($\text{4}$).     

The [4.4.4.4]Fenestranes and[2.2.2.2]paddlane. Prospects for the realization of planar tetracoordinate carbon?

Semi-empirical (MINDO/3 and UNDO) MO calculations on highly strained planar tetracoordinate carbon candidates indicate the central carbons in $\text{cis}$- [4.4.4.4] fenestrane ($\text{1}$) to have pyramidal ($\text{1a}$) and in trans-[4.4.4.]fenestrane ($\text{2}$) to have distorted tetrahedral ($\text{2a}$) geometries. In [2.2.2.2]paddlane ($\text{3}$), the two central carbons are pentacoordinate. Each is nearly coplanar with four carbon neighbours; additionally, the two bridgehead carbons are connected by a single bond ($\text{3a}$).     

Resolution of N-benzyl-N-(1,2-dihydro-2-oxoquinolin-1-yl)glycine

The $\text{N}$$\text{N}$ chiral axis in the title glycine derivative has allowed its resolution into enantiomers: the barrier Δ G^≠ for racemisation (rotation around the $\text{N}$$\text{N}$ bond) is 26.2 Kcal mol^?1.     

Interconversion and preparative separation of enantiomeric enamides

Barriers to rotation about the CN single bond of enamides (Table 1) are rationalised. The barriers of $\text{7}$ and $\text{8}$ allow separations of the enantiomers.     

Photodecomposition of selenosulfonates and their facile photoaddition to alkenes 1

Phenyl areneselenosulfonates ($\text{1}$) are very photosensitive and easily undergo photodecomposition via initial homolysis of the SeS bond. In the presence alkenes this facile photodissociation of $\text{1}$ can be used to initiate a free radical chain reaction (eq 6) that leads to addition of $\text{1}$ to the alkene to form β-phenylselenosulfones ($\text{2}$). The photoaddition requires much shorter reaction times than the non-photolytic addition of $\text{1}$ to alkenes described recently.²     

Useful synthetic reagents derived from 1-triisopropylsilylpropyne and 1,3bis-[triisopropylsilyl]propyne,direct, stereoselective synthesis of either Z or E enynes

Lithio reagents derived from 1-triisopropylsilylpropyne ($\text{1}$) and 1,3-$\text{bis}$-[triisopropylsilyl]propane ($\text{3}$) are effective for the synthesis of $\text{Z}$ or $\text{E}$ terminal enyne units (CHCHCCH) and for carboncarbon bond formation with halides, aldehydes, ketones, epoxides, and α,β-enones.     

Dedoublement et configuration absolue de la methyl-3 δ3(3a)-hydrindenone-4.etude de l'isomerisation en methyl-3 δsu3a(7a)-hydrindenone-4.

During the hydrogenation of the Δ^3(3a)-4-hydrindenones $\text{1}$ or $\text{3}$ on Pd or Ni, we observe a shift of the double bond to Δ^3a(7a)-4-hydrindenones $\text{2}$ and $\text{4}$. The absolute configuration established for ketones $\text{1}$ and $\text{2}$ shows that the reaction is a suprafacial process. By deuteriation experiments, we observe that the reaction is irreversible and occurs with a molecular hydrogen exchange.     

Oxidative cyclization of 5,6-dihydroxyalkenes promoted by Cr(VI) oxo species: A novel cis-2,5-disubstituted tetrahydrofuran synthesis

Oxidative cyclization of isomeric 5,6-dihydroxyalkenes of type $\text{1}$ derived from neryl and geranyl acetates with Cr(VI) oxo species afford cis-THF diols of type $\text{2}$ (syn addition across the double bond) with >99.5% stereospecificity.     

Reaction of bistrifluoromethylaminosulphenyl chloride with fluoro-olefins and hexafluorobut-2-yne under free-radical conditions

Reaction of bistrifluoromethylaminosulphenyl chloride with unsymmetrical fluoro-olefins in daylight or under photochemical conditions gives both possible 1:1 adducts ($\text{ca}$. 1:1 ratio) arising from homolytic fission of the SCl bond. Addition to octafluorobut-2-ene and hexafluorobut-2-yne gives mixtures of the $\text{syn}$- and $\text{anti}$- adducts.     

Generation of an active acyl species from stable 1-methyl-2-acyl-1h-imidazoles

1-Methyl-2-(1′-cyano-1′-trimethylsilyloxy)alkyl-1H-imidazoles ($\text{2}$) were easily prepared from the corresponding stable carbonyl compounds, 1-methyl-2-acyl- ¹H-imidazoles ($\text{1}$). When the quarternary salts of $\text{2}$ were treated with various nucleophiles, reactive acyl species, which was presumed to be acylcyanide ($\text{12}$), was generated in situ under CC bond fission to result in producing the corresponding acylated compounds ($\text{5}$–$\text{10}$) in good yields.     

Acyl migration in 2-substituted-2-acylpropyl radicals. The reaction of organocobaloximes as mimicries of coenzyme-B12

Radical cleavage of the carbon—cobalt bond of 2-acetyl-2-methoxy-carbonylpropyl cobaloxime ($\text{1}$) and 2-benzoyl-2-phenylpropyl cobaloxime ($\text{5}$) gives the enones which are formed by the 1, 2-migration of acyl-group.