Hydrosilylation of bicyclo[2.2.1]heptene derivatives by trichlorosilane with the use of Ni catalytic systems A study of the stereochemistry of the process

Hydrosilylation of endo- and exo-cyanonorbornenes, endo-methylnorbornene and camphene by trichlorosilane on a Ni catalytic system was investigated. Based on the spectral data obtained from ¹³C and ¹H NMR studies, using Eu(fod)₃ as the shift reagent and by employing the double resonance technique, the stereochemistry of the process has been studied. Stereoselective exo-addition of hydrosilane to bicyclo[2.2.1]heptene derivatives has been noted.     

NMR–Untersuchungen an Dicyclopentadienderivaten: I—1H-NMR: Anwendung von paramagnetischen Verschiebungsreagenzien (Eu(fod)3) zur Vereinfachung der Spektren exo/endo-isomerer Diole

The determination of the stereochemistry of a series of exo/endo-isomeric dihydro- and tetrahydro-dicyclopentadiene-9.10-diols (exo/exo or endo/endo), using Eu(fod)₃ for separation of the signals in their ¹H n.m.r. spectra, is discussed in detail. The paramagnetic shift values ΔEu determined for half-molar ratios Eu(fod)₃/diol allow an unambiguous stereochemical assignment of the diols with regard to exo/endo isomerism. The ΔEu quantities are correlated with the distance H_i…O-atom (R_i).     

13C NMR spectroscopy of four tertiary methyl norbornenols and norbornanols

Carbon chemical shifts and direct ¹³C? ¹H coupling constants of 2-endo-methyl-5-norbornen-2-exo-ol, 2-exo-methyl-5-norbornen-2-endo-ol, 2-endo-methylnorbornan-2-exo-ol and 2-exo-methylnorbornan-2-endo-ol have been measured from single samples using a dual probe pulse Fourier transform method.     

Electron-impact induced fragmentation of dimethanonaphthalene-type compounds

The mass spectra of endo,endo-1,2,3,4,4a,5,8,8a-octahydro-1,4:5,8-dimethanonaphthalen-anti-2-01 (Ia) and its endo,exo-2-ol (IIa) and endo,exo-10-ol (IIIa) isomers have been examined. Fragmentation schemes have been constructed on the basis of metastable transition measurements, accurate mass determination and deuterium substitution. A presence of the double bond in the molecule and a favourable hydrogen atom orientation in the vicinity of the double bond play an important role in the ion degradation process.     

Reactions of mer(exo)‐ and mer(endo)‐[Co(dien)(dapo)X]2+ Isomers (X=OH,Cl, ONO2, N3)

Properties indirectly determined, or alluded to, in previous publications on the titled isomers have been measured, and the results generally support the earlier conclusions. Thus, the common five‐coordinate intermediate generated in the OH^?‐catalyzed hydrolysis of exo‐ and endo‐[Co(dien)(dapo)X]²⁺ (X=Cl, ONO₂) has the same properties as that generated in the rapid spontaneous loss of OH^? from exo‐ and endo‐[Co(dien)(dapo)OH]²⁺ (40±2% endo‐OH, 60±2% exo‐OH) and an unusually large capacity for capturing (R=[CoN₃]/[CoOH][]=1.3; exo‐[CoN₃]/endo‐[CoN₃]=2.1±0.1). Solvent exchange for spontaneous loss of OH^? from exo‐[Co(dien)(dapo)OH]²⁺ has been measured at 0.04 s^?1 (k₁, 0.50M NaClO₄, 25°) from which similar loss from the endo‐OH isomer may be calculated as 0.24 s^?1 (k₂). The OH^?‐catalyzed reactions of exo‐ and endo‐[Co(dien)(dapo)N₃]²⁺ result in both hydrolysis of coordinated via an OH^?‐limiting process =153 M ^?1 s^?1; =295 M ^?1 s^?1; K_H=1.3±0.1 M ^?1; 0.50M NaClO₄, 25.0°) and direct epimerization between the two reactants =33 M ^?1 s^?1; =110 M ^?1 s^?1; 1.0M NaClO₄, 25.0°). Comparisons are made with other rapidly reacting Co^III‐acido systems.     

Selective Hydrogen Chloride Elimination from Primary Chlorides Induced by the Fluoride Anion. Anchimeric participation of the chloromethyl group in the heterolytic opening of an epoxide. Stereospecific syntheses of 5,6-bis (methylidene)-syn-2-norbornen-7-ol and 5,6-bis (methylidene)-endo-3-chloro-exo-2-norbornanol

Syntheses of the alcohols 10 and 18 , and the corresponding ketones 11 and 19 are presented. Endo-5, exo-6-bis (chloromethyl)-endo-3-chloro-exo-2-norbornanol ( 16 ) and endo-5-(bromomethyl)-exo-6-(chloromethyl)-endo-3-chloro-exo-2-norbornanol ( 17 ) were obtained by HCl- and, respectively, HBr-addition to endo-5, exo-6-bis (chloromethyl)-exo-2, 3-epoxynorbornane ( 5 ). The Wagner-Meerwein rearrangement was precluded in these reactions probably because of the formation of a relatively stable chloronium ion 15 arising from the participation of the 1,4-chlorine atom of the endo-5-chloromethyl group in the heterolytic ring opening of the epoxide 5 . The ‘naked’ fluoride anion (excess CsF in DMF or KF in DMF with 18-crown-6-ether) permitted the selective elimination of 2 equivalents of HCl from 16 and yielded the chlorohydrin-diene 18 .     

Carbon Participation in the Solvolysis of Tertiary Norbornyl Derivatives Norbornanes. Part 15. 6-substituted 2-methylnorbornyl 2-exo- and 2-endo-2,4-dinitrophenyl ethers

The solvolysis rates and products of the tertiary 2-methyl-2-exo- and -2-endo-norbornyl 2,4-dinitrophenyl ethers 1 and 2 , (X = 2,4-(NO₂)₂₂C₆H₃O) have been determined. The different sensitivities of the rates of these ethers to the inductive effect of substituents at C(6) indicate that graded bridging of C(2) by C(6) occurs in the ionization of the exo-ethers 1 , not, however, in the ionization of the endo-ethers 2. In both cases hydrolysis leads to 2-methyl-2-exo-norbornanols only. Consequently, substitution takes place with retention at C(2) in the exo-series 1 and with inversion at C(2) in the endo-series 2. It is concluded that stereoelectronic and polar effects, rather than steric bulk effects, determine the high exo/endo rate ratios of the parent norbornyl derivatives 1a and 2a .     

Reductive Radical Cyclisations of Bromo Acetals and (Bromomethyl)silyl Ethers of Terpenoid Alcohols

The tin hydride promoted and the reductive vitamin B₁₂ catalysed radical cyclisation of mixed 2-bromo-acetaldehyde acetals and of (2-bromomethyl)dimethylsilyl ethers of allylic terpenoid alcohols has been investigated: 3-oxadeca-5,9-dien-l-yl radicals undergo 5-‘exo’ cyclisation to oxolanes (Scheme 4), 3-oxa-2-siladeca-5,9-dien-1-yl radicals sequential 6-‘endo’→5-‘exo’ tandem cyclisation to cis-3-oxa-4-silabicyclo[4.3.0]nonanes (Scheme 5), and 3-oxa-2-silatetradeca-5,9,13-trien-l-yl radicals sequential 6-‘endo’→6-‘endo’→5-‘exo’ triple cyclisation to trans-transoid-trans- 12-oxa-11-silatricyclo[7.4.0.0^2,6] tridecanes (Scheme 6).     

NMR-Untersuchungen an Dicyclopentadienderivaten: II.—13C-NMR: γ-gauche-Effekt in Abhängigkeit von der exo/endo-Isomerie an Dicyclopentadien diolen

The ¹³C FT n.m.r. spectra of some exo- and endo-dihydro- and tetrahydrodicyclopentadiene-9,10-diols(exo/exo or endo/endo) are studied and the chemical shifts of the C-atoms are assigned by application of Eu(fod)₃ paramagnetic shift investigations and additional chemical shift parameters. Thus relatively strong γ-effects up to 12,8 ppm were observed for the C-atoms 4, 5, 7, 9, 10 and 1, 3, dependent on the exo/endo configuration of the OH-groups and the attached 5-ring, giving an interesting insight into the gemetry of these norbornane systems.     

A Photoelectron-spectroscopic investigation of the Homoconjugative Interaction between π- and Walsh-Orbitals in endo- and exo-Cyclopropano-norbornene

Photoelectron spectra of endo- and exo-cyclopropano-norbornene ( = endo- and exo-tricyclo[3.2.1.0^2.4]octa-6-ene) show that a significant homoconjugation exists between the π-orbital of the double bond and the symmetric Walsh-es-orbital of the cyclopropane ring in the exo-isomer, whereas the interaction is negligeable in the endo-derivative.     

Base Hydrolysis of Pentaaminecobalt (III) Complexes: The [CoX(dien) (dapo)]n+ system. Part 3. The internal conjugate base mechanism

Azide anation and racemization of optically pure mer-exo(H)- and mer-endo(H)-[Co(OH)(dien)(dapo)]²⁺ ( A and B (X = OH), resp.; dien = N-(2-aminoethyl)ethane-1,2-diamine; dapo = 1,3-diaminopropan-2-ol) involve the same symmetrical pentacoordinate intermediate as the base hydrolyses of the corresponding mer-exo(H)- and mer-endo(H)-[CoX(dien)(dapo)]²⁺ species A and B , respectively, where X = Cl, Br, or N₃. The kinetic parameters of the anation process are fully compatible with the independently measured competition ratio. The rate data reveal that substitution of OH^? is unexpectedly fast, viz. it is not consistent with the usual sequence Br^? > Cl^? > H₂O > N > OH^?. This behavior is interpreted on the basis of an internal conjugate base mechanism which involves an amino-hydroxo/aminato-aqua tautomerism, viz. the reaction is actually an OH^? -catalyzed substitution of [CoH₂O(dien)(dapo)]³⁺ where deprotonation occurs effectively at the secondary-amine site NH of dien.     

Stereoselective Synthesis of 2,4,6-Trimethylcyclohex-4-ene-1,3-diol Derivatives and of polypropionate fragments with four contiguous stereogenic centers

The Diels-Alder adduct (±)- 3 of 2,4-dimethylfuran and 1-cyanovinyl acetate was converted stereoselectively into benzyl 6-(4-chlorophenylsulfonyl)-1,3-exo,5-trimethyl-7-oxabicyclo[2.2.1]hept-5-en-2-exo-yl ( 26 ) and -2-endo-yl ether ( 36 ). Addition of LiAlH₄ to the latter led to the 3-O-benzyl derivatives 28 and 37 of (1RS,2SR,3SR,6SR)- and (1RS,2SR,3RS,6SR)-5-(4-chlorophenylsulfonyl)-2,4,6-trimethylcyclohex-4-ene-1,3-diol, respectively. Methylenation of 6-exo-(4-chlorophenylthio)-1-methyl-5-methylidene-7-oxabicyclo[2.2.1]heptan-2-one ( 16 ), obtained by reaction of (±)- 3 with 4-Cl-C₆H₄SCl and saponification gave, 6-exo-(4-chlorophenylthio)-1-methyl-3,5-dimethylidene-7-oxabicyclo [2.2.1]heptan-2-one ( 43 ), the reduction of which with K-Selectride afforded 6-exo-(4-chlorophenylthio)-1,3-endo-dimethyl-5-methylidene-7-oxabicyclo[2.2.1]heptan-2-endo-ol ( 44 ). The 3-O-benzyl derivative 48 of (1RS,2RS,3RS,6SR)-5-(4-chlorophenylsulfonyl)- 2,4,6-trimethylcyclohex-4-ene-1,3-diol was derived from 44 via based-induced oxa-ring opening of benzyl 6-endo-(4-chlorophenylsulfonyl)-1,3-endo-5-endo-trimethyl-7-oxabicyclo[2.2.1]hept-2-endo-yl ether ( 49 ). Benzylation of 28 , followed by reductive desulfonylation and oxidative cleavage of the cyclohexene moiety afforded (2RS,3SR,4RS,5RS)-3,5-bis(benzyloxy)-2,4-dimethyl-6-oxoheptanal ( 32 ).     

Acid-Catalyzed Rearrangements of 5,6-exo-Epoxy-7-oxabicyclo[2.2.1]hept-2-yl Derivatives. Migratory Aptitudes of Acyl vs. Alkyl Groups in Wagner-Meerwein Transpositions

In the presence of HSO₃F/Ac₂O in CH₂CL₂, 2-exo- and 2-endo-cyano-5,6-exo-epoxy-7-oxabicyclo[2.2.1]hept-2-yl acetates ( 6a , b ) gave products derived from the epoxide-ring opening and a 1,2-shift of the unsubstituted alkyl group (σ bond C(3)–C(4)). In contrast, under similar conditions, the 5,6-exo-epoxy-7-oxabicyclo[2.2.1]heptan-2-one ( 6c ) gave 5-oxo-2-oxabicyclo[2.2.1]heptane-3,7-diyl diacetates 20 and 21 arising from the 1,2-shift of the acyl group. Acid treatment of 5,6-exo-epoxy-2,2-dimethoxy-7-oxabicyclo[2.2.1]heptane ( 6d ) and of 5,6-exo-epoxy-2,2-bis(benzyloxy)-7-oxabicyclo[2.2.1]heptane ( 6e ) gave minor products arising from epoxide-ring opening and the 1,2-shift of σ bond C(3)–C(4) and major products ( 25 , 29 ) arising from the 1,3-shift of a methoxy and benzyloxy group, respectively. Under similar conditions, 5,6-exo-epoxy-2,2-ethylenedioxy-7-oxabicyclo[2.2.1]heptane ( 6f ) gave 1,1-(ethylenedioxy)-2-(2-furyl)ethyl acetate ( 32 , major) and a minor product 33 , arising from the 1,2-shift of σ bond C(3)–C(4). The following order of migratory aptitudes for 1,2-shifts toward electron-deficient centers has been established: acyl > alkyl > alkyl α-substituted with inductive electron-withdrawing groups. This order is valid for competitive Wagner-Meerwein rearrangements involving equilibria between carbocation intermediates with similar exothermicities.     

Regio- and stereochemical aspects of bromochlorination of norbornene

Bromochlorination of norbornene whose chemo- and regio-selectivity is determined by the type of the halogenating reagent used was studied. Three isomeric bromochloronorbornanes (2-endo-bromo-3-exo-chloro-, 2-exo-bromo-3-endo-chloro-, and 2-exo-bromo-7-syn-chlorobicyclo[2.2.1.]heptanes), 2-exo-7-syn- and 2-exo-7-anti-dibromo- and-dichloronorbornanes, and 2-bromonortricyclane were isolated and characterized by¹H and¹³C NMR spectra. The spectral and structural characteristics of the resulting compounds are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2290–2295, November, 1998.     

Synthese und Hydrolyse von 6-exo-substituierten 2-Methyl-2-exo-norbornyl und 2-Methyl-2-endo-norbornyl-(2,4-dinitrophenyl)äthern Norbornane. 16. Mitteilung

The Synthesis and Hydrolysis of 6-exo-Substituted 2-Methyl-2-exo-norbornyl and 2-Methyl-2-endo-norbornyl 2,4-Dinitrophenyl Ethers The synthesis of the title compounds and their hydrolysis products in aqueous dioxane are described. Upon hydrolysis, the 2-exo-ethers 1 (X=N₂phO) as well as the 2-endo-ethers 2 (X=N₂phO) yield the corresponding 2-methyl-2-exo-norbornanols 3 only. Therefore, the 2-exo-ethers react with retention of configuration at C(2), the 2-endo-ethers 2 with inversion at C(2).     

La résonance magnétique du 77Se dans des composés organiques

⁷⁷Se n.m.r. spectra of twenty-six organoselenium compounds, including some with an endocyclic selenium atom, have been recorded. Our measurements complete the scale of chemical shifts previously established by McFarlane. It seems difficult to define a range of chemical shifts which is characteristic of the valency state of selenium or of its endo- or exocyclic position. Some results are discussed qualitatively. In the case of selenolo[2,3-b]thiophene, evidence has been obtained for a ⁴J[Se, H] coupling across the sulphur atom.     

Proximity Effects in Acid and Base-Catalysed Ether Formation

When heated with sodium ethoxide in ethanol 7-methylidenebicyclo[3.3.1]nonan-3-endo-ol (endo- 1 ) is converted into 1-methyl-2-oxa-adamantane ( 3 ). This reaction involves nucleophilic addition of a hydroxy group to an unactivated olefinic bond. Formation of the cyclic ether 3 also takes place when endo- 1 is heated in aqueous ethanol. This electrophilic addition is strongly catalysed by weak acids and suppressed by weak bases. These unusual reactions proceed more slowly with 7-methylbicyclo[3.3.1]non-6-en-3-endo-ol (endo- 2 ) and can be ascribed to a proximity effect. This follows from the IR . and NMR . spectra of endo- 1 and endo- 2 which show strong intramolecular hydrogen (OH-π) bonding. The unsaturated endo- and exo-alcohols 1 and 2 , respectively, undergo only exo-complexation with silver ion.     

Synthese von Triafulven-Vorstufen für Retro-Diels-Alder-Reaktionen

Synthesis of Triafulvene Precursors for Retro-Diels-Alder Reactions Triafulvene precursors exo? 15 and endo? 15 have been prepared by addition of dibromocarbene to benzobarrelene 12 followed by a lithium-halogen exchange, methylation, and elimination of HBr ( 12→13→14→15 ), (Scheme 2). Gas-phase pyrolysis of exo/endo-mixtures of 15 above 400° gave minor amounts of naphthalene ( 16 ), traces of a hydrocarbon C₄H₄ identified by MS (presumably triafulvene 1 ) and predominantly (36%) the isomerization product 17 (Scheme 3). In a second synthetic approach the well-known cycloheptatriene-norcaradiene equilibrium of type 26?27 has been utilised to prepare various endo-trans-3-(X-methyl) tricyclo[3.2.2.0^2,4]nona-6,8-dienes 31 (Scheme 5). However, numerous elimination experiments 31→9 failed so far. The structure of two rearrangement products 33 and 34 (Scheme 6) has been elucidated.     

Synthesis of (+)-1,3:2,5-dianhydroviburnitol ((+)-(1R,2R,3S,5R,6S)-4,7-dioxatricyclo[3.2.1.03,6]octan-2-ol)

Epoxidation of (?)-(1R,2R,4R)-2-endo-cyano-7-oxabicyclo[2.2.1]hept-5-en-2-exo-yl acetate ((?)-5) followed by saponification afforded (+)-(1R,4R,5R,6R)-5,6-exo-epoxy-7-oxabicyclo[2.2.1]heptan-2-one ((+)-7). Reduction of (+)-7 with diisobutylaluminium hydride (DIBAH) gave (+)-1,3:2,5-dianhydroviburnitol ( = (+)-(1R,2R,3S,4R,6S)-4,7-dioxatricyclo[3.2.1.0^3,6]octan-2-ol; (+)-3). Hydride reductions of (±)-7 were less exo-face selective than reductions of bicyclo[2.2.1]heptan-2-one and its derivatives with NaBH₄, AlH₃, and LiAlH₄ probably because of smaller steric hindrance to endo-face hydride attack when C(5) and C(6) of the bicyclo-[2.2.1]heptan-2-one are part of an exo oxirane ring.     

The Diels-Alder Reactivity of 2,2′-Ethylidenebis[3,5-dimethylfuran] and Exploratory Chemistry of the Mono-adducts

In the presence of Me₃Al, 1-cyanovinyl acetate added to 2,2′-ethylidenebis[3,5-dimethylfuran] ( 1 ) to give a 20:10:1:1 mixture of mono-adducts 4,5,6 , and 7 resulting from the same regiocontrol (‘para’ orienting effect of the 5-methyl substituent in 1 ). The additions of a second equiv. of dienophile to 4–7 were very slow reactions. The major mono-adducts 4 (solid) and 5 (liquid) have 2-exo-carbonitrile groups. The molecular structure of 4 (1RS,1′RS,2SR,4SR)-2-exo-cyano-4-[1-(3,5-dimethylfuran-2-yl)ethyl-7-oxabicyclo[2.2.1]hept-5-en-2-endo-yl acetate) was determined by X-ray single-crystal radiocrystallography. Mono-adducts 4 and 5 were saponified into the corresponding 7-oxanorbornenones 8 and 9 which were converted with high stereoselectivity into (1RS,1′SR,4RS,5RS,6RS)-4-[1-(3,5-dimethyl furan-2-yl)ethyl]-6-exo-methoxy-1,5-endo-dimethyl-7-oxabicyclo [2.2.1]heptan-2-one dimethyl acetal ( 12 ) and its (1′RS-stereoisomer 12a , respectively. Acetal hydrolysis of 12a followed by treatment with (t-Bu)Me₂SiOSO₂CF₃ led to silylation and pinacol rearrangement with the formation of (1RS,1′RS,5RS,6RS)-4-[(tert-butyl)dimethy lsilyloxy]-1-(3,5-dimethylfuran-2-yl)ethyl]-5-methoxy-6-methyl-3-methylidene- 2-oxabicyclo[2.2.1]heptane ( 16 ). In the presence of Me₃Al, dimethyl acetylenedicarboxylate added to 12 giving a major adduct 19 which was hydroborated and oxidized into (1RS,1′RS,2″RS,3″RS,4SR,4″RS,5 SR,6SR)-dimethyl 5-exo-hydroxy-4,6-endo-dimethyl-1-[1-(3-exo,5,5-trimeth oxy-2-endo,4-dimethyl-7-oxabicyclo[2.2.1]hept-2-yl)ethyl]-7-oxabicyclo [2.2.1]hept-2-ene-2,3-dicarboxylate ( 20 ). Acetylation of alcohol 20 followed by C?C bond cleavage afforded (1′RS,1″SR,2RS,2′″SR,3RS, 3″SR,4RS,4″SR,5RS)-dimethyl {3-acetoxy-2,3,4,5-tetrahydro-2,4-dimethyl-5-[1-(3-exo,5,5-trimethoxy ?2-endo,4-dimethyl-7-oxabicyclo[2.2.1]hept-1-yl)-ethyl]furan-2,5-diyl} bis[glyoxylate] ( 24 ).