Naturally-occurring acetylenic compounds and derivatives : Regio- and stereocontrolled chloroformylation of 2-(1-propynyl)thiophene and 2-phenyl-5-(1-propynyl)thiophene

2-Phenyl-5-(1-propynyl)thiophene (1), isolated from Coreopsis grandiflora, and 2-(1-propynyl)thiophene (5), an immediate precursor in the synthesis of junipal (2), were synthesized in high yield by a Pd-catalyzed reaction between propyne and 2-iodo-5-phenylthiophene (4) or 2-iodothiophene (6), respectively. Reaction of 5 with the Vilsmeier reagent derived from POCl₃ and N-methylformanilide (MFA) afforded a mixture from which it was possible to isolate (E)-3-chloro-2-methyl-3-(2-thienyl)acrolein (10) in 37.7% yield. The structure and stereochemistry of 10 was unequivocally established by X-ray diffraction of a single crystal of the 2,4-dinitrophenylhydrazone of 10. GLC analysis showed that 10 was contaminated by ca 7% with an isomer to which, on the basis of ¹H-NMR and mass spectra, the structure of (Z)-3-chloro-2-methyl-3-(2-thienyl)acrolein (11) was attributed.Contrary to what was expected from the literature, junipal (2) represented only a minor component in the reaction mixture obtained by the Vilsmeier reaction on 5.Reaction of 1 with POCl₃ and MFA afforded (44.6% yield) a (E)-3-chloro-2-methylacrolein to which the structure 15 was attributed. Compound 15 was also contaminated by ca 10% of an isomer 16, which very probably corresponded to the (Z)-stereoisomer of 15.     

Synthesis and Cytotoxicity of 3-(Hetarylthio)-1-propynyl(trimethyl)silanes

We have developed a two-step method for synthesis of 3-(hetarylthio)-1-propynyl(trimethyl)silanes from thiols in a phase-transfer catalysis system HCCCH₂Br-solid K₂CO₃-18-crown-6-toluene followed by reaction with n-BuLi-Me₃SiCl in ether or THF. We have observed that 3-[1,3-bis(trimethylsilyl)-2-propynyl]thioindole displays high cytotoxicity in HT-1080 and MG-22A tumor cell lines.     

Synthesis of some substituted 1-(2-propynyl)-4-piperidones

Summary Some 1-(1,2-dimethyl-2-propynyl)-4-piperidones were synthesized, and the effect of substitution in the piperidine ring on the reversible cyclization of unsaturated-alkylamino ketones into 4-piperidones was investigated.     

Synthesis of 10-propargylfolic acid from 2-amino-6-(bromomethyl)-4(1h)-pteridinone

6-(Bromomethyl)-2,4-pteridinediamine hydrobromide (1) is readily converted to 2-amino-6-(bromomethyl)-4(1H)-pteridinone hydrobromide (2) by treatment with 48% hydrobromic acid. Compound 2 is of interest for direct attachment of the (2-amino-3,4-dihydro-4-oxo-6-pteridinyl)methyl group to appropriate side-chain precursors of analogues of folic acid, particularly those bearing functional groups incompatible with conditions required for hydrolytic deamination of the corresponding 2,4-diaminopteridine analogues. An example of the use of 2 in this connection is demonstrated through synthesis of 10-propargylfolic acid.     

Synthesis and structural characterization of alkaline-earth-metal bis(amido)silane and lithium oxobis(aminolato)silane complexes

Several of alkaline-earth-metal complexes [(η(2):η(2):μ(N):μ(N)-Li)(+)](2)[{η(2)-Me(2)Si(DippN)(2)}(2)Mg](2-) (4), [η(2)(N,N)-Me(2)Si(DippN)(2)Ca·3THF] (5), [η(2)(N,N)-Me(2)Si(DippN)(2)Sr·THF] (6), and [η(2)(N,N)-Me(2)Si(DippN)(2)Ba·4THF] (7) of a bulky bis(amido)silane ligand were readily prepared by the metathesis reaction of alkali-metal bis(amido)silane [Me(2)Si(DippNLi)(2)] (Dipp = 2,6-i-Pr(2)C(6)H(3)) and alkaline-earth-metal halides MX(2) (M = Mg, X = Br; M = Ca, Sr, Ba, X = I). Alternatively, compounds 5-7 were synthesized either by transamination of M[N(SiMe(3))(2)](2)·2THF (M = Ca, Sr, Ba) and [Me(2)Si(DippNH)(2)] or by transmetalation of Sn[N(SiMe(3))(2)](2), [Me(2)Si(DippNH)(2)], and metallic calcium, strontium, and barium in situ. The metathesis reaction of dilithium bis(amido)silane [Me(2)Si(DippNLi)(2)] and magnesium bromide in the presence of oxygen afforded, however, an unusual lithium oxo polyhedral complex {[(DippN(Me(2)Si)(2))(μ-O)(Me(2)Si)](2)(μ-Br)(2)[(μ(3)-Li)·THF](4)(μ(4)-O)(4)(μ(3)-Li)(2)} (8) with a square-basket-shaped core Li(6)Br(2)O(4) bearing a bis(aminolato)silane ligand. All complexes were characterized using (1)H, (13)C, and (7)Li NMR and IR spectroscopy, in addition to X-ray crystallography.     

Syntheses and structures of methyltris(pyrazolyl)silane complexes of the group 6 metals

The methyltris(3,5-dimethylpyrazolyl)silane ligand, TpsMe2, was readily prepared by the metathesis reaction of methyltrichlorosilane with 3 equiv of lithium 3,5-dimethylpyrazolate. The octahedral tricarbonyl complexes (TpsMe2)M(CO)3 were synthesized either by ligand exchange with the labile nitrile adducts M(CO)3(NCR)3 (M = Cr, Mo, R = Me; M = W, R = Et) or thermally by direct substitution on the hexacarbonyls M(CO)6 (M = Cr, Mo). The three new complexes were characterized by a combination of analytical and spectroscopic techniques, including electrospray ionization mass spectrometry and single-crystal X-ray diffraction. They are all isostructural and display in the solid state the expected distorted octahedral geometries with facially coordinated tris(pyrazolyl)silane ligands. Crystallographic data were used to calculate the ligand cone angles (251-264 degrees) in (TpsMe2)M(CO)3 and also to estimate a value of 1.59 A for the covalent radius of octahedral W(0).     

Pd(II)-mediated coupling of 1,1-dimethyl-2-propynyl acetate with itself and 1-decene

Heating 1,1-dimethyl-2-propynyl acetate (1) with PdCl₂(MeCN)₂ (0.05–0.1 mol equiv) and MeCN alone afforded (E)-2,7-dimethylocta-2,4,6-trien-3,6-diyl diacetate (2) (yield ca. 20%) and with 1-decene (7 mol equiv) present (E)-2-methyltetradeca-2,4-dien-3-yl acetate (7) (30%) together with 2 (12%).     

Triethoxy(3-isothiocyanatopropyl)silane

The reaction of triethoxy(3-aminopropyl)silane with carbon disulfide andortho-chloroethyl formate in absolute ethanol gave triethoxy(3-isothiocyanatopropyl)silane for the first time. The presence of SCN and (C₂H₅O)₃Si groups in this compound enabled us to use it for the preparation of adsorbents and polymer coatings with biocidal activity.Irkutsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, 664033 Irkutsk. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 11, pp. 2681–2682, November, 1992.     

Tetrakis(1‐naphthylamino)silane and its tetrahydrofuran trisolvate

In both title structures, C₄₀H₃₂N₄Si and C₄₀H₃₂N₄Si·3C₄H₈O, the angles around the Si atom deviate significantly from the tetrahedral value [104.34 (7)–116.63 (7)° in the nonsolvate and 99.91 (15)–116.85 (15)° in the solvate]. The amino H atoms in the solvated structure are involved in hydrogen bonding with two of the tetrahydrofuran solvent molecules.     

On the Mechanism of Intramolecular Cyclization of Dialkyl(2-propynyl)[3-alkenyl(or aryl)-2-propynyl]-ammonium Salts

Given are experimental data indicating that base-catalyzed intramolecular cyclization of ammonium salts containing a 2-propynyl-like group together with a 3-alkenyl- or 3-aryl-2-propynyl group follows a concerted mechanism involving the 3-alkenyl- or 3-aryl-2-propynyl moiety as π⁴-fragment.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 3, 2005, pp. 369–371.Original Russian Text Copyright © 2005 by E. Chukhadzhyan, Gevorkyan, El. Chukhadzhyan, Kinoyan.     

The dissociative adsorption of silane and disilane on Si(100)-(2 x 1)

We investigate the dissociative adsorption of silane and disilane on Si(100)-(2 x 1) using pseudopotential planewave density functional theory calculations. These are important steps in the growth of silicon films. Although silane has been studied computationally in some detail previously, we find physisorbed precursor states for the intradimer and interdimer channels. The silane energetics calculated here are in good agreement with experimental data and previous theoretical estimates and provide us with a useful reference point for our disilane calculations. Disilane has not been studied as intensively as silane. We investigate both silicon-silicon bond cleavage and silicon-hydrogen bond cleavage mechanisms, and for each we investigate intradimer, interdimer, and inter-row channels. As in the case of silane, we also find precursor states in the adsorption path in agreement with molecular beam experiments. The qualitative picture that emerges is that adsorption takes place through a weakly bound precursor state with a transition state to chemisorption that is low lying in energy relative to the gas phase. This is in good agreement with experimental data. However, the calculated energetics are only in fair agreement with experiments, with our transition state to chemisorption being about 0.02 eV above the gas phase while experimentally it is estimated to be approximately 0.28 eV below the gas phase. This suggests that accurate theoretical characterization of these weakly bound precursor states and the adsorption barriers requires further computational work.     

Conformational Equilibrium of 4-Hydroxy- and 4-Acetoxy-4-(3-aryloxy-1-propynyl)-1-(2-ethoxyethyl)piperidinium Salts in Solution

4-Hydroxy- and 4-acetoxy-4-(3-aryloxy-1-propynyl)-1-(2-ethoxyethyl)piperidine hydroclorides in aprotic solvents give rise to equilibrium mixtures of two epimers. In the case of the acetoxy derivatives (in CDCl₃) the equilibrium is displaced toward the less stable epimer. This may be due to considerable contribution of the skewed boat conformer with intramolecular hydrogen bond.     

Hydrolysis and etherification of (o-carboranylisopropyl)dichloro(methyl)silane

The behavior of (o-carboranylisopropyl)dichloro(methyl)silane in hydrolysis and etherification reactions has been studied. (o-Carboranylisopropyl)(methyl)silanediol and (o-carboranylisopropyl)diethoxy(methyl)silane have been obtained for the first time and characterized.