摘要:

The photosensitized (electron transfer) reactions of 3-phenyl-2,3-dihydrobenzofuran (8a), 5-methyl-3-phenyl-2,3-dihydrobenzofuran (8b),cisandtrans-2-methoxy-1-phenylindane (9,cisandtrans), 3,3-diphenyltetrahydrofuran (10), and 2,2-diphenyl-1-methoxycyclopentane (11) have been studied using 1,4-dicyanobenzene as an electron-accepting photosensitizer and acetonitrile–methanol (3:1) as solvent. These reaction conditions cause carbon–carbon bond cleavage of analogous acyclic β,β-diphenylethyl ethers to give products derived from the diphenylmethyl radical and the α-oxycarbocation intermediates. The purpose of this study was to determine if this reaction could be applied to five-membered cyclic derivatives to give 1,5-radical cations.The primary products from8aand8bwere the dehydrogenated, aromatized 3-phenylbenzofurans14aand14b. These products react further; continued irradiation gave the methanol adducts,cisandtrans-2-methoxy-3-phenyl-2,3-dihydrobenzofuran (15aand15b,cisandtrans). The only observed reaction of the indanes (9,cisandtrans) wascis-transisomerization. Deuterium was incorporated at the bis-benzylic position of8and9when the irradiation was carried out in acetonitrilemethanol-O-d. These results are consistent with reversible deprotonation from the radical cations. There was no evidence for carbon–carbon bond cleavage with either8or9. The relative rate, deprotonation faster than carbon–carbon bond cleavage, is explained in terms of the conformation of the bond that cleaves in relation to the singly occupied molecular orbital (SOMO) of the radical cation. Oxidation potential measurements support the conclusion that the SOMO of8and9is largely associated with the fused phenyl ring and is therefore orthogonal to the benzylic carbon–carbon bond. Irradiation ofcisortrans-2-methoxy-3-phenyl-2,3-dihydrobenzofuran (15a,cisortrans), under these conditions, leads tocis–transisomerization. The mechanism in this case involves the reversible loss of methanol. There is evidence that the addition of methanol to14involves the sensitizer radical anion –14radical cation pair.In contrast with the fused bicyclic systems, the monocyclic tetrahydrofuran10and the methoxycyclopentane11both cleave under these conditions; the products are the expected acetals22and29formed from the intermediate 1,5-radical cations. In10and11the SOMO, which is largely associated with the diphenylmethyl moiety, can overlap with the adjacent carbon–carbon bond and cleavage occurs as in analogous acyclic systems. Both10and11are relatively stable to irradiation under conditions that are identical except with acetonitrile as solvent (without methanol). We found no evidence for cyclization of the intermediates (1,5-radical cation or 1,5-diradical) into the terminal phenyl ring.

ISSN:0008-4042    

DOI:10.1139/v87-455

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The crystal structures of the compounds SBr3AsF6(1), SeI3AsF6(2), SeI3SbF6(3), and TeI3SbF6(4) are reported and the quantitative preparation of the hitherto unknown3and4from SbF5and the respective elements in SO2are given. Crystal data are as follows:1, monoclinic, space groupP21/c, witha = 8.015(1) Å,b = 9.342(1) Å,c = 12.126(2), β = 97.81(1)°, andZ = 4;2, monoclinic, space groupP21/c, witha = 8.380(2) Å,b = 10.237(1) Å,c = 12.524(1) Å, β = 99.36(1)°, andZ = 4;3, monoclinic, space groupP21/c, witha = 8.548(2) Å,b = 10.297(6) Å,c = 12.877(8) Å, β = 98.70(3)°, andZ = 4;4, monoclinic, space groupP21/c, witha = 8.463(1) Å,b = 10.676(2) Å,c = 13.121(4) Å, β = 100.05(1), andZ = 4. Compounds1,2,3, and4are isostructural and were refined to a finalRvalues of 0.040, 0.051, 0.047, and 0.037, respectively. The structures of these salts consist of essentially discrete MX3+cations and M′F6−anions (M = S, Se, Te; X = Br, I; M′ = As, Sb) with some cation–anion interactions. TheSeI3+bond distances and angles were essentially identical in both AsF6−and SbF6−salts (average Se—I distance and I—Se—I angle for AsF6−salt; 2.508(2) Å, 102.4(1)° and for SbF6−salt; 2.512(1) Å, 102.3(1)°). Similarly the average Te—I bond distance and I—Te—I angle for TeI3SbF6were 2.666(1) Å and 99.8(1)° which are essentially identical to those in the previously reported TeI3AsF6. The average S—Br distance and Br—S—Br angle were 2.142(6) Å and 103.4(2)° in SBr3AsF6. Estimates of the S—I bond distance and I—S—I bond angle in the as yet unknown SI3M′F6are made from the extrapolation of MX3+data. The bond distances observed in the simple MX3+cations (M = S, Se, Te; X = Cl, Br, I) with anions of very low basicity are within 0.02 Å of the corresponding distances calculated by the Schomaker–Stevenson equation. The observed and estimated bond distances in SBr3+, SI3+, and SeI3+are significantly longer than the corresponding S—Br, S—I, and Se—I distances in S7I+, S7Br+, and Se6I22+. This observation is used to support the thesis that the long intra-cationic halogen–chalcogen contacts in polychalcogen–halogen cations are weakly bonding, and responsible for the cluster-like nature of these cations. The heats of formation of1and2from their respective elements and AsF5were estimated.

ISSN:0008-4042    

DOI:10.1139/v87-456

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Crystals of [1-(N,N-dimethylammonium)ethyl]ferrocene tartrate dihydrate are triclinic, space groupP1,a = 7.235(1),b = 11.372(2),c = 12.724(3) Å, α = 90.78(1), β = 102.75(1), γ = 91.76(2)°,V = 1020.3 Å3at 20 ± 2 °C withZ = 2. The structure was solved by direct methods. The correct enantiomer was chosen based on full-matrix least-square refinements of each enantiomer. For the correct enantiomer,R = 0.031,Rw = 0.035 for 11052 reflections withI ≥ 2σ(I). Although the two crystallographically independent units of the complex in the structure are chemically equivalent, they are structurally different. The absolute configuration of the amino-substituted carbon atom is (S), and that of the tartrate anion is (R,R). The mean ferrocenyl Fe—C bond lengths are 2.037(2) Å and 2.027(3) Å for each molecule, respectively. The NMe2group is located outside the planes of the cyclopentadienyl rings. The tartrate ions are connected through water molecules by hydrogen bonds.

ISSN:0008-4042    

DOI:10.1139/v87-457

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The apparent molecular polarization at infinite dilution of acetoacetanilide, and benzoylacetanilide in five constant-ratio mixtures of triethylamine in benzene leads to the inference that the equilibrium constants of the association process between the anilide and the amine in benzene are 357 and 600, and that the dipole moments of the complexes formed are 4.43 and 5.25 D, respectively.

ISSN:0008-4042    

DOI:10.1139/v87-458

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The methyl glycoside (1) of the α-L-Rhap-(1 → 2)-α-L-Rhap-(1 → 2)-α-L-Rhap-(1 → portion of the group-specific, common antigen polysaccharide of Group B Streptococci has been synthesized. The key compound of the synthesis was methyl 3,4-di-O-benzyl-α-L-rhamnopyranoside (4). Controlled acetolysis of4gave 1,2-di-O-acetyl-3,4-di-O-benzyl-α-L-rhamnopyranose (10), which upon reaction with4under catalysis by trimethylsilyl trifluoromethanesulfonate (TMS-Tf) yielded the α-(1 → 2)-linked dirhamnoside. Subsequent rhamnosylation followed by deprotection gave1. TMS-Tf was also used in rhamnosylation reactions with tetra-O-acetyl-α-L-rhamnopyranose. Acetylation of acceptor alcohols was found to be a major side reaction in the TMS-Tf assisted glycosylations. One-dimensional nuclear Overhauser enhancement differential spectroscopy indicated that, in solution,1takes up a bent instead of an extended conformation.

ISSN:0008-4042    

DOI:10.1139/v87-459

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Anodic oxidation of lactams in the presence of halide ions produced excellent yields of bicyclic compounds with reactants having rings in the range of eight to ten atoms (C7to C9). Smaller rings did not react to form bicyclic products and larger rings gave reduced yields. Attempts were made to cyclize non-cyclic amides and to bicyclize cycloheptyl and cyclooctyl acetamide with limited success.

ISSN:0008-4042    

DOI:10.1139/v87-460

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The effect of electron pair donor solvents on methylene reactivity has been theoretically studied by means ofabinitiomethods, using the split valence 3-21G basis set. The calculations have been done on the well-known methylene addition to ethylene, taking one water molecule in order to represent the donor solvent. We have shown that the process takes place via the formation of a reversible complex between water and methylene, the formation of this complex permitting to explain the experimentally observed decrease of methylene's electrophilicity. The analysis of the variation of the electronic charge density and of the solvation parameters along the reaction coordinate have also allowed to interpret the reaction in terms of the transfer of an electrophile (methylene) from a nucleophile (water) to another nucleophile (ethylene).

ISSN:0008-4042    

DOI:10.1139/v87-461

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The surface tension and density of the LaCl3–NaCl system were determined as a function of temperature by the maximum bubble pressure technique. The surface tension and density were found to vary linearly with temperature (1123 < T < 1248 K). At constant temperature, the surface tensions of LaCl3–NaCl melts showed a small negative deviation from Guggenheim's Equation.

ISSN:0008-4042    

DOI:10.1139/v87-462

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

To improve the synthesis of perchlorato complexes of Cd(II) and Hg(II), reactions of Cl2O6with CdCl2, CdCO3, Cd(NO3)2•nH2O, HgCl2, Hg(ClO4)2•6H2O, and Hg(NO3)2•H2O were tried. The complexes Cd(ClO4)2, ClO2Cd(ClO4)3, NO2Cd(ClO4)3, HgClClO4, Hg(ClO4)2, and (NO2)2Hg(ClO4)4were characterized. Among these complexes only HgClClO4is ionic (HgCl+is a polymeric chain); the others are perchlorato complexes. Cd(ClO4)2is related to the layered complexes M(ClO4)2(M = Co, Ni, Zn) in which ClO4is a bridging tridentate. Hg(ClO4)2is close to HgCl2or Hg(SR)2(SR: thiocarbamate); ClO4is a monodentate and it interacts with neighbouring molecules. In the salts ClO2Cd(ClO4)3, NO2Cd(ClO4)3, and (NO2)2Hg(ClO4)4the anions have polymeric arrangements; their structures are analogous to those of ACuCl3, NO2Co(ClO4)3, and (NO2)2Cu(ClO4)4, respectively.

ISSN:0008-4042    

DOI:10.1139/v87-463

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

We have carried out the deprotecting of variousN-protected amino acids and dipeptides by subjecting them to hydrogen transfer with several palladium catalysts supported on different solids. The hydrogen donor itself has been used "insitu" to reduce the corresponding Pd salt on the support. We have also analyzed the effect of various factors on the deprotecting rate for Z-glycine. Such factors include the procedure used in synthesizing the catalysts ("insitu" or by conventional reduction), the type of support, hydrogen donor, promoting effect of alkaline hydroxides, type of reactor (closed or open), and magnetic or ultrasonic agitation. We have found that the ease of adsorption of the protected amino groups (Z—NH—) is fundamental in accounting for the order of deprotecting rates found. We have compared the activity of new catalysts in the deprotecting process with that of a commercial one containing 10% Pd over carbon, supplied by Fluka (ref. 75990).

ISSN:0008-4042    

DOI:10.1139/v87-464

出版商:NRC Research Press    

年代:1987

数据来源: NRC