Photoaddition with 1,2-bis(trimethylsiloxy)cyclobutene: a versatile entry to the stereocontrolled total synthesis of various sesquiterpenes and diterpenes

The photocycloaddition of 2-cyclohexenones to 1,2-bis(trimethyl-siloxy)cyclobutene provides a short and versatile route to adequately functionalized decalins for the total synthesis of members of the following terpene classes: the eudesmanes, the eudesmanolides, the guaianes, the labdanes and the nagilactones. Regioselective and stereoselective manipulation of these key intermediates is discussed.     

Studies on the thermal ring-opening reactions of cis-3,4-bis(organosilyl)cyclobutenes

Three cis-3,4-bis(organosilyl)cyclobutenes were synthesized, and their thermal ring-opening reactions were studied. The ring-opening reaction of cis-3,4-bis(trimethylsilyl)cyclobutene proceeded remarkably faster than that of cis-3,4-dimethylcyclobutene. The significant rate acceleration was explained by assuming (i) stabilization of the transition state by electron delocalization from the cyclobutene HOMO to the Si-CH3 sigma* orbital, (ii) destabilization of the ground state by intramolecular interaction between the C-Si sigma orbitals and the pi orbital of cyclobutene, and (iii) through-space steric repulsion of the two bulky trimethylsilyl groups in a cis arrangement. The ring-opening reaction of unsymmetrical cis-3,4-bis(arylsilyl)cyclobutenes having electronically different arylsilyl groups was also examined. The inward preference increased in the order, p-CH3OC6H4-Si, C6H5-Si, p-CF3C6H4-Si, supporting the interpretation of the origin of the inward preference of silyl substituents on the basis of a stabilizing interaction between the cyclobutene HOMO and the Si-C sigma* orbital at the transition state.     

Reactions of 1,2-di(2-thienyl)-3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]cyclobutene

Reactions of a sterically protected 1,2-di(2-thienyl)-3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]cyclobutene were investigated. The diphosphinidenecyclobutene reacted with elemental sulfur or transition metal reagents to form a thiaphosphirane derivative or the corresponding transition metal complexes, respectively. Reactions of the di(2-thienyl)diphosphinidenecyclobutene with butyllithium followed by treatment with electrophiles afforded functionalized di(2-thienyl)diphosphinidenecyclobutene derivatives.     

Synthesis of naphtho[b]cyclobutenes from 1,2-bis(3-propynol)benzenes

We have demonstrated that the reaction of benzene-bridged bis(propargyl alcohol)s with chlorodialkylphosphines exclusively afforded 3,8-bis(dialkylphosphinyl)naphtho[b]cyclobutenes via the [2+2] cycloaddition of 1,2-bis(α-phosphinylallenyl)benzenes. Dephosphinylation of the product has also been achieved.     

Synthesis of 1,2-bis(methoxyamino)cycloalkanes from alicyclic 1,2-bis(hydroxyamines)

Derivatives of 1,4-dihydroxypiperazine-2,3-dione were obtained by reaction of cis-1,2-bis(hydroxyamino)cycloalkanes with diethyl oxalate. Their alkylation with CH₂N₂ or Mel afforded 1,4-dimethoxypiperazine-2,3-diones. Hydrolysis of the latter gave 1,2-bis(methoxyamino)cycloalkanes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 925–929, April, 1996.     

Chemistry of 2,5-bis(trimethylsiloxy)furans. III: Synthesis of γ-hydroxybutenolides

γ-Hydrobutenolides were obtained from the reaction of substituted 2,5- bis(trimethylsiloxy)furans with aldehydes and ketones using titanium tetrachloride activation. Similarly, α,β-unsaturated carbonyl compounds reacted as a Michael receptor with the title compounds to give γ-hydroxybutenolides.     

Chemistry of 2,5-bis(trimethylsiloxy) furans. I: Preparation and diels-alder reactions

A number of substituted 2,5-bis (trimethylsioloxy) furans were prepared from the corresponding succinic anhydrides, and were found to be reactive dienes for the Diels-Alder reaction with electron - withdrawing dienophiles, giving p-quinones and hydroquinones.     

Synthesis and reactivity of 1,2-bis(chlorodimethylgermyl)carborane and 1,2-bis(bromodimethylstannyl)carborane

The 1,2-bis(chlorogermyl)- (1) and 1,2-bis(bromostannyl)carborane (2) have been prepared by the reaction of dilithio-o-carborane with Me(2)GeCl(2) and Me(2)SnBr(2), respectively. Compounds 1 and 2 are found to be good precursors for the synthesis of a variety of cyclization compounds. The Wurtz-type coupling reaction of 1 and 2 using sodium metal afforded the four-membered digerma compound 3 and five-membered tristanna compound 4, respectively. The salt elimination reactions of 1 and 2 using Li(2)N(t)Bu and Li(2)PC(6)H(5) afforded the cyclic products [structure: see text]. The 1,2-bis(dimethylgermyl)carborane 9 and 1,2-bis(dimethylstannyl)carborane 10 were prepared by the reaction of 1 and 2 with sodium cyanoborohydride. The reactions of 9 and 10 with Pd(PPh(3))(4) afforded the bis(germyl)palladium 12 and bis(stannyl)palladium 13 complexes, respectively.     

Silicon-carbon unsaturated compounds: XXX. thermal isomerization of 1-mesityl-3-phenyl-1,2-bis(trimethylsilyl)-1-silacyclopropene and 2-mesityl-2-(phenylethynyl)hexamethyltrisilane

The thermolysis of 1-mesityl-3-phenyl-1,2-bis(trimethylsilyl)-1-silacyclopropene at 280°C afforded 1-mesityl-3,3-dimethyl-4-phenyl-5-(trimethylsilyl)-1,3-disilacyclo-4-pentene and 1-mesityl-1,3-bis(trimethylsily)-1-silaindene. Similar thermolysis of 2-mesityl-2-(phenylethynel)hexamethyltrisilane produced the same products.     

Synthesis of 1,2 difluoro-1,2-bis(pentafluorophenyl)dichlorane

1,2-Difluoro-1,2-bis(pentafluorophenyl)dichlorane is a new class of organic polyvalent chlorine compound. The closeness of the retention time of this compound and that of chloropentafluoro- benzene made its purification difficult. All attempts to obtain this compound in high yield have failed. 1,2-Difluoro-1,2-bis- (pentafluorophenyl)dichlorane is prepared by fluorination of chloropentafluorobenzene at 128°C with elemental fluorine. It has been characterized by ¹⁹F n.m.r., i.r., mass spectroscopy and elemental analysis.     

The reaction of para-tolydiazonium tetrafluoroborate with bis (dinitrogen)-bis(1,2-bis(diphenylphosphino)ethane)molybdenum

Reactions of para-tolyldiazonium tetrafluoroborate with trans-Mo(N₂)₂ (dppe)₂ (where dppe = 1,2-bis(diphenylphosphino ethane) result in the oxidation of the molybdenum complex with complete loss of dinitrogen. A similar reaction occurs with MoBr(N₂)(dppe)₂.     

Crystal chemistry of protonated 1,2-bis(di-R-aminomethyl)benzenes. Part V. [1,2-bis(diethylaminomethyl)-3,6-dichlorobenzene:1,2-bis(diethylaminomethyl)-3,4,6-trichlorobenzene]perchlorate mixed crystals

The mixed crystals of 1,2-bis(diethylaminomethyl)-3,6-di- and 3,4,6-trichloro-benzene perchlorate at 0.5:0.5 ratio have been studied using X-ray diffraction and FT-IR spectroscopy. The molecules of di- and tri-chloro derivatives are distributed randomly in the crystal lattice; however, this disorder manifested mainly by a partial occupation of the chlorine atom at C(4) and by relatively big atomic temperature parameters even at 99 K, particularly for the oxygens of the perchlorate anion. The proton in the [NHN]⁺ bond refined close to the equidistant position between the nitrogens. The conformations of the diethylaminomethyl substituents are pseudo-symmetrical relative to the plane and twofold axis passing through the midpoint of the hydrogen bond. The IR spectrum of the crystals shows a broad intense band and an intense continuous absorption indicating relatively high proton polarizability in the intramolecular hydrogen bond. In acetonitrile and in chloroform, the proton in the intramolecular hydrogen bond also shows a very high proton polarizability demonstrated by the continuous absorption in the IR spectrum.     

Crystal chemistry of protonated 1,2-bis(di-R-aminomethyl)benzenes. Part VI: 1,2-bis(diethylaminomethyl)-4,5-dichlorobenzene perchlorate

The crystals of a 1:1 complex of 1,2-bis(diethylaminomethyl)-4,5-dichlorobenzene perchlorate with HClO₄ were studied using X-ray diffraction and FT-IR spectroscopy. There are two symmetry-independent ionic pairs in the crystal, monoclinic, space group P2₁/n. In both symmetry-independent cations, the diethylaminomethyl substituents are in a similar Z conformation relative to the phenyl moieties, however significant conformational differences in the diethylaminomethyls have been noted. The diethylaminomethyls are linked by intracationic ⁺N–H⋯N hydrogen bonds of 2.758(9) and 2.721(7) Å in two symmetry-independent cations. The protons in these H-bonds are disordered in two off-center sites, which is most likely to be connected with the considerable disorder of the perchlorate anions. The IR spectrum of the crystals shows a broad intense band and a relatively intense continuous absorption indicating relatively large proton polarizability in the intramolecular hydrogen bond of a medium length.     

Kinetics of the thermal gas-phase isomerization of 1,2-epoxycyclohexane

The kinetics of the gas-phase decomposition of 1,2-epoxycyclohexane has been studied over the temperature range 680–740 K at pressures between 1.6 and 6 torr. Isomerization to cyclohexanone and 2-cyclohexen-1-ol accounts for ca. 97% of the primary reaction products and occurs by first-order, homogeneous, nonradical processes:      

Preparations and properties of polymers containing 3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]-1,2-di(2-thienyl)cyclobutene moieties

Reaction of 1,8-bis[5-{(2,4,6-tri-t-butylphenyl)phosphinoethynyl}-2-thienyl]octane with butyllithium followed by treatment with 1,2-dibromoethane afforded a new polymer containing 3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]-1,2-di(2-thienyl)cyclobutene units. The polymer was allowed to react with bis(benzonitrile)dichloropalladium to give the polymer complex. A Sonogashira coupling reaction between ethynyltrimethylsilane and 4-bromonitrobenzene proceeded in DMF at 100 °C to give 4-nitro(trimethylsilylethynyl)benzene in the presence of the polymer complex, CuI, and triethylamine.     

The structure and racemization of 1,2-bis(pentaphenylphenyl)benzene

1,2-Bis(pentaphenylphenyl)benzene (2) was synthesized by the cycloaddition of 1,2-bis(phenylethynyl)benzene and tetracyclone. Its X-ray structure was determined, and the molecule adopts a C₂-symmetric conformation in the crystal. Monomethoxy and dimethoxy derivatives of compound 2 were also prepared, and dynamic NMR studies of these compounds yielded a free energy of activation for racemization (ΔG³_rac) of 20.3?kcal/mol at 423?K. The results are compared with estimates of ΔG³_rac for 2 by various DFT methods.     

Radical ions in photochemistry 10. The photosensitized (electron-transfer) isomerization of 1,2-diphenylcyclopropanes.

The photoisomerization of the 1,2-diphenylcyclopropanes in polar solvent sensitized by 1-cyano- and 1,4-dicyanonaphthalene proceeds via an electron-transfer mechanism. An analysis of photo-CIDNP results provide details regarding the intermediates.     

A thermal decomposition study on cobalt(II) complexes of 1,2-bis(IMINO-4'-antipyrinyl)ethane

The phenomenological, kinetic and mechanistic aspects of thermal decomposition of perchlorate, nitrate, chloride, bromide and iodide complexes of cobalt(II) with the Schiff base 1,2-bis(imino-4'-antipyrinyl)ethane (GA) have been studied by TG and DTG analyses. The kinetic parameters like the activation energy, pre-exponential factor and entropy of activation were calculated. The decomposition reactions follow 'random nucleation with one nucleus on each particle - Mampel model'. This revised version was published online in July 2006 with corrections to the Cover Date.     

Study of anionic copolymerization of α,ω-bis(trimethylsiloxy)polydimethylsiloxane with organocyclosiloxanes

Anionic copolymerization of α,ω-bis(trimethylsiloxy)polydimethylsiloxane with 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane in the presence of α,ω-bis(tetramethylammoniumoxy)polydimethylsiloxanolate was studied by means of gas-liquid chromatography, gel-permeation chromatography, and ²⁹Si NMR techniques. It was shown that the equilibrium homopolymerization of the cyclic comonomer initially took place and it was not until its conversion became greater than 90% that linear poly(dimethylsiloxane) was involved in the reaction. It was found that a constant molecular mass is reached before the linear siloxane-cyclosiloxane equilibrium and a random distribution of units in the copolymer are established. The dependence of the total amount of cyclosiloxanes at equilibrium on the dimethylsiloxy-to-methylvinylsiloxy unit ratio in the reaction system was determined.