Delocalization energy of the cyanomethyl radical: Kinetics of thermal diastereoisomerization of cis- and trans-1,2-dicyano- and 1 ,2-dicyano-1-methylcyclopropanes

Arrhenius parameters for the thermal first-order geometrical isomerization of 1,2-dicyanocylopropanes(I) have been determined in naphthalene solution over the range 208.0–259.5° in both directions:

where θ = 4.575T × 10^?3 and k is in sec^?1. Since this enthalpy of activation is lower than that of the geometrical isomerization of 1,2 - dideuterocyclopropane by 17.8±0.4 kcal, it may be concluded that replacement of hydrogen by the cyano group leads to an energy lowering of 8.9$\text{kcal}\text{mol}$.Kinetic parameters have been determined in the gas-phase at two temperatures, 217.8° and 259.5°: log k_t,c = 13.73– 45.64/θ; log k_c,t =13.86–44.43/θ.The rates of cis-trans interconversion of 1,2 - dicyano - 1 - methyl - cyclopropane(II) relative to those of I have been obtained by examination of mixtures of both substances in t-butylbenzene solution at 259.5°: 1.2-dicyano, k_t,c= 1.25 and k_c,t = 3.53; 1,2 - dicyano - 1 - methyl, k_t,c = 8.09 and k_c,t = 22.35 × 10^?5 sec^?1. The rate acceleration by methyl amounts to a factor of 6.4, corresponding to ΔΔG^≠ = 1.96$\text{kcal}\text{mol}$. A preliminary examination of optically active material leads to a minimum R_A = 1.37 favoring rotation of (CN)(H) over (CN)(CH₃).     

Mechanistic Aspects of Inorganic Reactions. ACS Symposium Series 198 : (Ed. D.B. Rorabacher and J.F. Endicott), American Chemical Society,Washington DC, 1982, x + 486 pages, $ 58.95 ($ 48.95, U.S.A. and Canada). ISBN 0-5412-0734-8.

Norbornadiene (NBD) is more easily displaced from PtMe₂ (NBD) by other ligands than is cyclooctadiene (COD) from PtMe₂ (COD). cis-PtMe₂L₂ (L = py, $\text{1}\text{2}$tmen, $\text{1}\text{2}$en, NH₃, DMSO) have been prepared in this way. cis-PtMe₂py₂ is very reactive toward oxidative addition. Pyridine can usually be removed from the platinum(IV) products using acid. NBD is even more readily displaced from Pt(CF₃)₂ (NBD), giving cis-Pt(CF₃)₂L₂ (L = py, $\text{1}\text{2}$tmen, $\text{1}\text{2}$en, NH₃, DMSO, NCR, DMF, CN^?, I^?, acac^?). cis-Pt(CF₃)₂py₂ with CF₂I gives fac-Pt(CF₃)₃py₂I.     

Stable isobenzofuran endoperoxide and its use for oxidation of olefins ans aromatic compounds

1,3-Di-tert-butylisobenzofuran reacts with singlet oxygen with rate constant of 2.8 x 10⁹ M^?1 sec^?1 to give stable endoperoxide $\text{4}$. Thermolysis of the endopepoxide ($\text{4}$) in the ppesence of norbornene and naphthalene gave the corrpesponding epoxide and naphthols, respectively. Addition of Pd(OAc)₂ improved the yield of naphtols considepably.     

Photochemical studies. Irradiation induced transformations of 1,2-dihydrophthalides

The photochemical behavior of $\text{cis}$-1,2-dihydrophthalide ($\text{1}$) and its 1,2-trimethylene derivative ($\text{4}$) was studied. Besides bicyclo[2.2.0]hexene formation in both cases, ($\text{1}$) transforms into its $\text{trans}$ isomer ($\text{3}$) whereas ($\text{4}$) undergoes a 1,2-shift to ($\text{7}$).     

Synthesis of 4-substituted cis,cis-1,6-cyclodecadienes via cycloalkylation

Cycloalkylation of dimethyl malonate and tosylmethylisocyanide with $\text{cis}$,$\text{cis}$-1,9-dibromonona-2,7-diene has demonstrated the feasibility of direct cyclization as a route to functionalized $\text{cis}$,$\text{cis}$-1,6-cyclodecadienes.     

The synthesis of cis- and trans-1,2-dibromocyclopropane

A preparative route to cis- and trans-1,2-dibromocyclopropane ($\text{1}$) was developed via the Hunsdiecker reaction of silver cyclopropane-1,2-dicarboxylate ($\text{2}$). Cis- and trans-$\text{2}$ gave the same ratio of cis- and trans-$\text{1}$ (1:3.2). The mechanism of this reaction is briefly discussed.     

Stereochemical studies—76 saturated heterocycles—63 : synthesis of cis- and trans-n-methyl- and n-benzyl-4.5- and 5,6-tetramethylenetetrahydro-1,3-oxazines; an x-ray study of n-benzyl-cis-4,5-tetramethylenetetrahydro-1,-3-oxazinium- picrate

- The corresponding $\text{cis}$- and $\text{trans-N}$-methyl- and $\text{N}$-benzyl-5,6- and 4,5-tetramethylenetetrahydro-l,3-oxazines $\text{(5a,b-8a,b)}$were synthesized from $\text{cis}$- and $\text{trans-N}$-methyl and$\text{N}$-benzyl-2- aminomethyl-1-cyclohexanols $\text{1a,b,2a,b}$, from $\text{cis}$- and $\text{trans-N}$-methyl- and $\text{N}$benzyl -2-hydroxymethyl-1-cyclohexylamines$\text{(3a,b,4a,b)}$ by reaction with formaldehyde. The aminoalcohols $\text{1a,2a,3a,b}$and $\text{4a,b}$ were prepared in considerably higher yields than in earlier procedures. NMR spectroscopy showed that the $\text{cis}$ isomers of the synthesized oxazines were conformationally homogeneous in solution, and their preferred conformation (inside or outside) depended on the steric requirement of the groups attached to the anellation points, whereas a bulky C-2 substituent had no influence on the predominant conformation. The structure of $\text{N}$-benzyl-$\text{cis}$-4,5-tetramethylenetetrahydro-1,3-oxaziniumpicrate $\text{(7b)}$. determined by X-ray diffraction analysis, was in agreement with the predominant N-outside conformation of the corresponding base, established by means of NMR spectroscopy.     

Thiosulfonium ions. Methylthiolation of 3-methylthio-1-butene and cis- and trans-1-methylthio-2-butene

Whereas sulfenyl reagents commonly add to carbon double bonds, addition to sulfur of 3-methylthio-1-butene precedes attack at carbon to give allylic thiosulfonium ions that form reversibly and which rearrange rapidly to $\text{trans}$-2-butenyl analogs. Likewise, rearrangement of $\text{cis}$- to $\text{trans}$-1-methylthio-2-butene occurs by way of thiosulfonium ions.     

Study of thermal decomposition of poly-(vinyl chloride)-type polymers with the use of model substances-V: Pyrolysis of cis-5-chloro-3-heptene and cis- and trans-5-acetoxy-3-heptene in the phase

The gas phase pyrolyses of cis-5-chloro-3-heptene (in the range 267–337°) and cis- and trans-5-acetoxy-3-heptene (300–378°) are homogeneous unimolecular first-order reactions with rate constants given respectively by: log k = (12·03 = 0·13) - (36·2 ± 0·4)/2·303 RT and (12·80 ± 0·11) - (43·0 ± 0·3)/2·303 RT. (Frequency factors in sec^?1 units, activation energies in kcal mol^?1.) No significant differences were found between the rates of decomposition of cis and trans isomers of 5-acetoxy-3-heptene. From the decomposition of these models of poly(vinyl chloride) and poly(vinyl acetate), some conclusions about the role of internal unsaturated groups in the thermal decomposition of both polymers were drawn. The possibility that groups with cis internal double bonds are the most labile structures in a poly(vinyl) chloride macromolecule is discussed.     

Substituted cyclononatetraenes and nonafulvenes

Reaction of $\text{cis}$,$\text{cis}$,$\text{cis}$,$\text{cis}$-[9]annulene anion ($\text{1}$) with electrophiles ($\text{2a}$-$\text{d}$) leads to substituted $\text{cis}$,$\text{cis}$,$\text{cis}$,$\text{cis}$-1,3,5,7-cyclononatetraenes ($\text{3a}$-$\text{d}$) which are precursors for the preparation of 10- and 10,10′-donor-substituted nonafulvenes (e.g. $\text{7b′}$$\text{e′}$). The influence of solvent and temperature on the ¹H-nmr spectra of the nonafulvenes $\text{7b′}$-$\text{h′}$ has been investigated.     

The preferred conformation of cis-1,4-dihydro-4-tritylbiphenyl: A flexible cyclohexa-1,4-diene

X-ray crystallographic and solution ¹H n.m.r. studies of $\text{cis}$-1,4-dihydro-4-tritylbiphenyl (2) both suggest the presence of an almost planar cyclohexa-1,4-diene ring (α_mean = 1975°).⁴     

Conformational effects in compounds with 6-membered rings—X : Synthesis of cis- and trans-3,5-di-t-butylthian and sulphonium salt formation from thians

Convenient stereospecific syntheses of cis- and trans-3,5-di-t-butylthian (1 and 2) have been developed. The reaction between anancomeric thians with unhindered S atoms and methyl iodide has been investigated and a range of kinetic (from 6.5 up to 11:1) and thermodynamic (from 1.25 up to 2.8:1) stereoselectivities, with equatorial $\text{S}\text{+}$-Me always favoured, have been observed. It is concluded that the observed stereoselectivities are best explained by steric hindrance at the axial site on sulphur and that twist conformers do not contribute significantly to the reactivity of most thians in such reactions. The contrast between relative kinetic and thermodynamic stereoselectivities shown in the reaction between methyl iodide and either N-methylpiperidines or thians is explained by different directions of approach to these 6-membered rings during axial attack.Acid anhydrides have been isolated from the oxidation of β-diketones by ozone and by chromic acid.     

Complementary short syntheses of (±)-methyl shikimate

Two syntheses of (±)-methyl shikimate from the adduct of furan and methyl acrylate are described. One requires the regioselective hydroxylation of (±)-5β,6β-dihydroxy-$\text{O}$,$\text{O}$-isopropylidene-2-methoxycarbonylcyclohexa-1,3-diene and the other $\text{cis}$-dihydroxylation of (±)-5-hydroxy-1-methoxycarbonylcyclohexa-1,3-diene.     

Molecular structure and conformation of cis-1,3- dichloro-1-propene as determined by gas phase electron diffraction

The molecular structure and conformation of cis-1,3-dichloro-1-propene have been determined by gas phase electron diffraction at a nozzle temperature of 90°C. The molecule exists in a form in which the chlorine atom of the methyl group and the carbon-carbon double bond are gauche to one another. The results for the distance (r_g) and angle (∠_α) parameters are: r(C-H) = 1.078(10)Å, r(CC) = 1.340(5)Å, r(C-C) = 1.508(7)Å, r( =C-Cl) = 1.762(3)Å, r(C-Cl) = 1.806(3)Å, ∠Cl-C-C = 111.7°(1.8), ∠(CC-C) = 125.5°(1.5), ∠Cl-CC = 124.6°(1.6) and ∠H-C-Cl = 111°(5). The torsion-sensitive distances close to the gauche form can be approximated using a dynamic model with a quartic double minimum potential function of the form V(Φ) = V₀[1 + ($\text{Φ}\text{Φ}{}_0$⁴ - 2($\text{Φ}\text{Φ}{}_0$)²], where V_o = 1.1(8) kcal mol^?1 and Φ₀ = 56°(5) (Φ = 0 corresponds to the anti form).     

Synthesis of the 7-cis isomer of the natural leukotriene d4

Methyl 5(S), 6(S)-oxido-11-oxo-7-cis-9-trans-undecadienoate $\text{5}$ was prepared and used for the synthesis of the novel 7-cis-LTD₄ ($\text{9}$) as well as, after isomerization to the all-trans dienal ester $\text{3}$, for that of the natural leukotrienes.     

The 185-nm photochemistry of 2,3-diazabicyclo[2.2.1]heptene and of its denitrogenation products bicyclo[2.1.0]pentane and cyclopentene

The 185-nm denitrogenation of 2,3-diazabicyclo[2.2.1]heptene ($\text{1}$) afforded bicyclo[2.1.0]-pentane ($\text{2}$) and cyclopentene ($\text{3}$) presumably via a “hot” cyclopentane-1,3-diyl diradical ($\text{8}$); 1,4-pentadiene ($\text{4}$) and methylenecyclobutane ($\text{5}$) were secondary products of the 185-nm photolysis of ($\text{2}$) and ($\text{3}$).     

Synthesis and chemistry of HC(SO2F)3 and cis- and trans(HO)2TeF4

HC(SO₂F)₃ has been prepared and characterized. It turned out to be a strong acid, comparable to mineral acids. In aqueous solution the salts of the type Cs⁺C(SO₂F)₃^? are formed. The anion, as found by crystal structure analysis contains planar CS₃ configuration.Quite in contrast to these findings HC(OSO₂F)₃ is not even soluble in water.Derivatives of HC(SO₂F)₃ have been prepared so far CH₃C(SO₂F)₃ FC(SO₂F)₃ ClC(SO₂F)₃ BrC(SO₂F)₃ JC(SO₂F)₃The heavier halogen derivatives ( Cl, Br, J ) are oxidizing agents (‘positive halogen’).A mixture of $\text{cis-}$ and $\text{trans-}$ (HO)₂TeF₄ is obtained if HOTeF₅ and Te(OH)₆ are melted together. The mixture of the isomeres have been transfered into the corresponding silylesters $\text{cis}$- and $\text{trans-}$ (R₃SiO)₂TeF₄, which could be separated by fractional crystallisation and distillation.Without conformational change the pure silylesters have been reacted back to pure $\text{cis}$- (HO)₂TeF₄ and $\text{trans}$- (HO)₂TeF₄ by means of anhydrous HF. Both $\text{cis-}$ and $\text{trans}$ (HO)₂TeF₄ have been reacted with ClF to give $\text{cis}$- and $\text{trans}$- (ClO)₂TeF₄, yellow liquids. The latter react with elemental bromine to the rather unstable $\text{cis-}$ and $\text{trans-}$ (BrO)TeF₄, red liquids.Starting with $\text{cis}$-(HO)₂TeF₄ and XeF₂ a polimer Xenon compound of the formula

All materials have been characterized by melting point and vapour pressure, 19 F - nmv spectroscopy, vibrational spectroscopy, and elemental analysis.     

Enantiomerically pure phosphonate analogues of cis- and trans-4-hydroxyprolines

All the enantiomers of O,O-diethyl 4-hydroxypyrrolidinyl-2-phosphonates, phosphonate analogues of cis- and trans-4-hydroxyprolines, have been obtained for the first time. The synthetic strategy involved 1,3-dipolar cycloaddition of (R)- and (S)-N-(1-phenylethyl)-C-(diethoxyphosphoryl)nitrones to allyl alcohol and separation of the corresponding O,O-diethyl 5-(hydroxymethyl)-2-(1-phenylethyl)isoxazolidinyl-3-phosphonates, which were subsequently mesylated and hydrogenated to undergo intramolecular cyclisation. Absolute configurations of the enantiomeric proline phosphonates were established after N- and O-derivatization with (S)-O-methylmandelic acid employing the Trost model.     

Singlet oxygenation of cis,cis-1,5-cyclooctadiene: a convenient synthetic entry into 5,8-difunctionalized oxygen derivatives of 1,3-cyclooctadiene

The 6-hydroperoxy-1,4-cyclooctadiene ($\text{2}$), which is formed in the photosensitized oxygenation of 1,5-cyclooctadiene ($\text{1}$), affords on further singlet oxygenation 5,8-dihydroperoxy-1,3-cyclooctadiene ($\text{3}$), which via triphenylphosphine reduction leads to $\text{cis}$-5,8-dihydroxy-1,3-cyclooctadiene ($\text{4}$) and subsequent pyridinium chlorochromate oxidation to 1,3-cyclooctadien-5,8-dione ($\text{8}$).