Reaktionen mit phosphororganischen Verbindungen, 49. Synthese und 1H-NMR-Spektren von (3-Acylbicyclo[2.2.1]hept-5-en-2-yl)phosphonsäureestern

Reactions with Organophosphorus Compounds, 49. Synthesis and ¹H NMR Spectra of (3-Acylbicyclo[2.2.1]hept-5-en-2-yl)phosphonates Reaction of the (E)-(β-acylvinyl)phosphonates 1 with cyclopentadiene yields the isomeric norbornylphosphonates 2 (endo-acyl, exo-P) and 3 (exo-acyl, endo-P) in a 7:3 ratio. With 1,3-cyclohexadiene the corresponding bicyclooctenyl derivatives 7 and 8 are obtained from 1a . The (Z)-phosphinylacrylate 4 gives with cyclopentadiene the isomers 5 (exo-CO₂Me, exo-P) and 6 (endo-CO₂Me, endo-P) in nearly equal amounts. The configuration of the cycloadducts has been proved by ¹H NMR spectroscopy.     

Solvolysen von 4-Alkylidenbicyclo[3.2.0]hept-2-en-6-olen. Synthese von 1-Vinylfulvenen und 8,8-Diphenylheptafulven

Solvolysis of 4-Alkydenbicyclo[3.2.0]hept-2-en-6-oles. Synthesis of 1-Vinylfulvenes and 8,8-Diphenylheptafulvene Four 4-alkylidenebicyclo[3.2.0]hept-2-en-6-ones 2–5 , obtained via ketene cycloaddition to fulvenes, were reduced to separated mixtures of the ‘endo’ -alcohols ‘endo’- 6 to ‘endo’- 9 (68–73%) and ‘exo’- 6 to ‘exo’- 9 (3–20%). Treatment of some of these alcohols with (CF₃SO₂)₂O in CH₂Cl₂/pyridine caused a spontaneous solvolysis to yield unsaturated 7-membered rings as pyridinium triflates 10–12 or 1-vinylfulvenes 13 and 14 , a new class of reactive tetraenes: Both ‘endo’- 9 and ‘exo’- 9 , having two methyl groups at C(7), were converted into the vinylfulvene 13 (≈ 80%). The alcohols with two H-atoms at C(7) exhibited a stereochemically controlled reaction selectivity, inasmuch as ‘endo’- 6 to ‘endo’- 8 afforded only the corresponding 7-membered-ring pyridinium salts 10–12 (66–79%), while ‘exo’- 6 produced only the vinylfulvene 14 (77%). A stereoelectronic control argument explains the C(1), C(5)-bond cleavage with ‘endo’- B and ‘endo’– 6 -‘endo’- 8 , as well as the C(1), C(7)-bond cleavage with ‘exo’- B , ‘exo’- 6 , and with both ‘endo’- and ‘exo’- 9 . Thermolysis (120°) of the pyridinium triflates 10 and 11 yielded the 3-isopropenyl-cycloheptatrienes 18 and 19 , respectively (≈90%); similar conditions (145°) applied to the triflate 12 produced the doubly cyclized fluorene derivative 21 (60%). When the iodide 22 derived from the triflate 12 with Nal was heated in refluxing toluene, 8,8-diphenylheptafulvene ( 23 , 86%) was obtained.     

Extensive hydrogen and halogen bonding,and absence of intramolecular hydrogen bonding between alcohol and nitro groups in a series of endo‐nitronorbornanol compounds

The influence of the substituent at the C2 position on the hydrogen‐bonding patterns is compared for a series of five related compounds, namely (±)‐3‐exo,6‐exo‐dibromo‐5‐endo‐hydroxy‐3‐endo‐nitrobicyclo[2.2.1]heptane‐2‐exo‐carbonitrile, C₈H₈Br₂N₂O₃, (II), (±)‐3‐exo,6‐exo‐dibromo‐6‐endo‐nitro‐5‐exo‐phenylbicyclo[2.2.1]heptan‐2‐endo‐ol, C₁₃H₁₃Br₂NO₃, (III), (±)‐methyl 3‐exo,6‐exo‐dibromo‐5‐endo‐hydroxy‐3‐endo‐nitrobicyclo[2.2.1]heptane‐2‐exo‐carboxylate, C₉H₁₁Br₂NO₅, (IV), (±)‐methyl 3‐exo,6‐exo‐dibromo‐7‐diphenylmethylidene‐5‐endo‐hydroxy‐3‐endo‐nitrobicyclo[2.2.1]heptane‐2‐exo‐carboxylate, C₂₂H₁₉Br₂NO₅, (V), and (±)‐methyl 3‐exo,6‐exo‐dibromo‐5‐endo‐hydroxy‐3‐endo‐nitro‐7‐oxabicyclo[2.2.1]heptane‐2‐exo‐carboxylate, C₈H₉Br₂NO₆, (VI). The hydrogen‐bonding motif in all five compounds is a chain, formed by O—H...O hydrogen bonds in (III), (IV), (V) and (VI), and by O—H...N hydrogen bonds in (II). All compounds except (III) contain a number of Br...Br and Br...O halogen bonds that connect the chains to each other to form two‐dimensional sheets or three‐dimensional networks. None of the compounds features intramolecular hydrogen bonding between the alcohol and nitro functional groups, as was found in the related compound (±)‐methyl 3‐exo,6‐exo‐dichloro‐5‐endo‐hydroxy‐3‐endo‐nitrobicyclo[2.2.1]heptane‐2‐exo‐carboxylate, (I) [Boeyens, Denner & Michael (1984b). J. Chem. Soc. Perkin Trans. 2, pp. 767–770]. The crystal structure of (V) exhibits whole‐molecule disorder.     

Inductivity and Bridging in 2-Bicyclo[2.2.2]octyl Cations. Polar Effects,Part 11

The solvolysis rates and products of several 6-substituted 2-exo- and 2-endo-Bicyclo[2.2.2]octyl p-toluenesulfonates, 12 and 13 , respectively, are reported. Inductivity, as measured by the reaction constants ρ_I, is considerably less in the exo-series 12 (ρ_I = ?1.50) than in the corresponding 2-exo-norbornyl p-toluenesulfonates 1 (ρ_I= ?2.0). It is proposed that, for geometrical reasons, bridging of the cationic center C(2) by C(6) is not as strong in the bicyclooctane series 12 as it is in the norbornane series 1 . On the other hand, inductivity is higher in the 2-endo-bicyclooctane series 13 (ρ_I= ?1.0) than in the corresponding 2-endo-norbornane series 3 (ρ_I = 0.78), probably, because in the former case bridging of C(6) is less hindered by the departing anion. The relative yields of exo- and endo-substitution products from the series 12 and 13 , are in accord with graded bridging of C(6) in the incipient bicyclooctyl cations. But almost constant bridging of C(2) by C(7) is indicated in the ionization of the 2-endo-bicyclooctane series 13 . Consequently, in the free unsubstituted bicyclooctane cation C(2) is bridged symmetrically by C(6) and C(7), in contrast to the current concept of ‘non-classical’ two-electron-three-center bonding.     

Norbornanes. Part 20. Inductivity and bridging in 2-norbornyl cations

The solvolysis rates and products of several 1-substituted 2exo- and 2-endo-norbornyl p-toluenesulfonates 7 and 8 , respectively, have been determined. Hydrolyses of these epimeric tosylates yielded rearranged products in varying amounts, except when the substituent was COOCH₃ or CN. The logarithms of the rate constants (log k) for the endo-series 8 correlated linearly with the corresponding inductive constants σ with a reaction constant ρ_I of ?1.24. On the other hand, log k values for the exo-series 7 appear to fit two regression lines, the first line (ρ_I = ?1.90) defined by the tosylates that ionize, with rearrangement, to the tertiary cations 11 , the second (ρ_I = ?1.86) by the tosylates 7 (R = H, COOCH³, and CN) that ionize to an asymmetrically bridged secondary cation 19 . These results confirm the unique participation of C(6) with a ρ_I of ?2.00 in the ionization of 2-exo-nor-bornyl tosylate.     

The 1H NMR spectra of some norbornene derivatives,a LIS study

The ¹H NMR spectra of 2-exo-hydroxymethyl-3-endo-methylnorbornene and the corresponding 2-endo-3-exo isomer have been completely assigned with the aid of lanthanide reagents. This enabled a full analysis of the unusual spectrum of 2-exo-hydroxy-methyl-3-endo-methylnorbornene to be undertaken, confirming the proposed structure. The ΔEu values for 2-exo-hydroxymethyl-3-endo-methylnorbornene and the 2-endo-3-exo-isomer have been used to test the effect of rotational averaging on the calculated pseudo contact shifts. Good agreement is obtained for a dynamic model in which the Eu atom exchanges between two sites on the oxygen atom of the OH bond, and in which the rotational equilibrium about the CH? CH₂OH bond is explicitly considered.     

Perfluoroalkyl derivatives of nitrogen. Part LI [1]. Reaction of the N-halogenobistrifluoromethylamines (CF3)2NX (X=Cl,Br) with norbornadiene

Reaction of the amines (CF₃)₂NX (X=Cl,Br) with norbornadiene either in solvent (CH₂Cl₂) at ?78 °C in the dark or in the vapour phase at 20 °C in daylight gives a mixture of 3-halogeno-5-($\text{NN}$-bistrifluoromethylamino)nortricyclene ($\text{exo}$, $\text{endo}$-and $\text{exo}$, $\text{exo}$-isomers) and $\text{exo}$-5-($\text{NN}$-bistrifluoromethylamino)- $\text{anti}$-7-halogenonorbornene in quantitative yield formed $\text{via}$ halonium ion addition to the diene. The reaction of the amine (CF₃)₂NBr in solvent Me₂O or Et₂O at ?78 °C in the dark gives the same products in low yield, together with 3-bromo-5-alkoxynortricyclene ($\text{exo}$, $\text{endo}$- and $\text{exo}$, $\text{exo}$-isomers) and the amine (CF₃)₂NR (R=Me, Et) in high yield.     

Secondary 2-Norbornyl Cation Intermediates Substituted at C(5) and C(7) by Electron-withdrawing Groups. Addition of fluorosulfuric acid to unsaturated norbornane derivatives

Low temperature (?130° to ?110°) addition of exo-norborn-5-en-2-ol ( 7 ) to excess HSO₃F in SO₂CIF yielded a mixture of exo-5-(fluorosulfonyloxy)-exo-2- and endo-2-norbornylhydroxonium ions ( 9+10 ) under kinetic control that was different from the mixture of 9+10 obtained by addition of endo-norborn-5-en-2-ol ( 8 ) to HSO₃F under kinetic control. These mixtures differed from the mixture of 9+10 observed at higher temperature (?80° to ?60°) (thermodynamic control). Addition of 3-nortricyclanol ( 23 ) or exo-2, 3-epoxynorbornane ( 24 ) to HSO₃F at -?120° ± 10° yielded a mixture containing the exo-2-(fluorosulfonyloxy)-anti-7- and syn-7-norbornylhydroxonium ions ( 26+27 ) as major adducts. Qualitative rates of the isomerization of 26+27 to the more stable ions 9+10 and of the isomerization 9 ? 10 were evaluated. The solvolysis of 9+10 in HSO₃F yielded the exo-2, exo-5- and exo-2, endo-5-norbornanediyl bis (fluorosulfates) ( 21+22 ). Norbornadiene and quadricyclane added 2 equivalents of HSO₃F and furnished kinetically a mixture of exo-2, anti-7- and exo-2, syn-7-norbornanediyl bis (fluorosulfates) ( 36+37 ) as major adducts. The latter 36+37 were isomerized into a kinetic mixture of the more stable isomers 21+22 . The rates of these isomerizations were compared. The use of DSO₃F and (exo-2-D)-norborn-5-en-2-ol ( 15 ) confirmed that heterolyses of the fluorosulfates were responsible for the observed isomerization; elimination-addition processes occurred but much more slowly. The results are interpreted in terms of substituted classical and σ-bridged secondary 2-norbornyl cation intermediates. It appears that the electron withdrawing substituents FSO₃ and H₂O⁺ (HO) destabilize the σ-bridged 2-norbornyl cation more at C(5) than C(7). If the σ-bridged ions 5-Z substituted at C(5) by Z = FSO₃ or H₂O⁺ (HO) are transition states in the isomerization of the corresponding classical ions 3-Z, 4-Z , the free enthalpy difference between the ‘non-classical’ σ-bridged ion and the classical ions is not higher than the energy barrier to the quenching of the latter intermediates by FSO in HSO₃F/SO₂CIF.     

Stereochemical studies. 81. Saturated heterocycles. 69 . Preparation of methylene-bridged 3,1-benzoxazines, 3,1-benzoxazin-2-ones and 3,1-benzoxazine-2-thiones

3-exo-Aminobicyclo[2.2.1]hept-5-ene-2-exo-carboxylic acid and ethyl 3-endo-aminobicyclo[2.2.1]heptane-2-endo-carboxylate ( 6 ) were reduced with lithium aluminum hydride to the corresponding bicyclic aminoalcohols 3 and 4 . These and the saturated endo-endo and exo-exo N-methylaminoalcohols 16 and 22 , respectively, were converted to methylene-bridged tetrahydro- ( 11 ) and hexahydro-3,1-benzoxazin-2-ones 12, 17, 23 and 3,1-benzoxazin-2-thiones 13, 14, 18, 24 . The exo-exo 3 and endo-endo 4 aminoalcohols were cyclized by means of ethyl arylimidates to tricyclic dihydro-1,3-oxazines 7a-d, 8a-d . The structures were confirmed by ir, ¹H and ¹³C nmr spectroscopy.     

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.     

Nucleophilic addition to C,C?double bonds. Part IX. Kinetics and mechanism of the base-catalyzed intramolecular cyclization of olefinic alcohols

The base-catalyzed intramolecular cyclization of polycyclic olefinic alcohols of type a (10-endo-hydroxy-anti^9,10-tricyclo [4.2.1.1^2,5]dec-7-en-9-ones (type h ), anti^9,10-tricyclo[4.2.1.1^2,5] dec-3-en-9-endo-ols (type j ), and anti^10,11-tricyclo[4.3.1.1^2,5]undec-3-en-10-endo-ols (type 1 )) to the ethers d and f , resp., has been studied. A mechanism for the nucleophilic addition of the corresponding alkoxide anion b to the isolated C,C? double bond is discussed. It is proposed that b is formed (fast acid/base equilibrium) in the first step. For the subsequent reaction sequence, there are two well distinguishable pathways: (a) Compounds with an additional carbonyl group ( h ) cyclize via a homoenolate-like intermediate c , which is protonated stereoselectively on the exo-side by the hydroxylic solvent. (b) Compounds without a carbonyl group ( j and l ) cyclize 10²-10⁴ times slower, and the reaction proceeds via a carbanion-like transition state e . The proton transfer from the hydroxylic solvent is clearly coupled with the C,O? bond formation. Steric compression in the olefinic alcohols a influences the cyclization rate: (a) Alcohols with a smaller ring ( h , X = CH₂CH₂) cyclize 70–200 times faster than the ones with a larger ring ( 1 , X = CH₂CH₂CH₂). (b) Replacement of the H-atom at the carbinol C-atom by a CH₃ group enhances the rate of ether formation by a factor of 50–100. Due to through-bond interactions between the C,C-double bonds, olefinic alcohols with an additional endocyclic C,C-double bond ( h and j , X = CH?CH) cyclize 20–300 times faster than the corresponding monoolefinic ones ( h and j , X = CH₂CH₂).     

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.     

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).     

Secondary α-deuterium kinetic isotope effects in [2+4] cycloaddition of (E)-2-phenylnitroethene to cyclopentadiene

Abstract  

Secondary α-deuterium kinetic isotope effects confirm that [2+4] cycloaddition between (E)-2-phenylnitroethene and cyclopentadiene occurs in concerted manner, on both the pathway leading to 6-endo-phenyl-5-exo-nitronorbornene and the pathway leading to the corresponding 6-exo-phenyl-5-endo-nitro isomer. According to Hammond terminology the transition states on competitive pathways should be considered in terms of symmetrical early states.     

Novel heterocyclic inhibitors of matrix metalloproteinases: three 6H‐1,3,4‐thiadiazines

The title compounds, (2S)‐N‐[5‐(4‐chloro­phenyl)‐2,3‐di­hydro‐6H‐1,3,4‐thia­diazin‐2‐yl­idene]‐2‐[(phenyl­sulfonyl)­amino]­pro­pan­amide, C₁₈H₁₇ClN₄O₃S₂, (I), (2R)‐N‐[5‐(4‐fluoro­phenyl)‐6H‐1,3,4‐thia­diazin‐2‐yl]‐2‐[(phenyl­sulfonyl)amino]­propan­amide, C₁₈H₁₇FN₄O₃S₂, (II), and (2S)‐N‐[5‐(5‐chloro‐2‐thienyl)‐6H‐1,3,4‐thia­diazin‐2‐yl]‐2‐[(phenyl­sulfonyl)­amino]­propan­amide, C₁₆H₁₅ClN₄O₃S₃, (III), are potent inhibitors of matrix metalloproteinases. In all three compounds, the thia­diazine ring adopts a screw‐boat conformation. The mol­ecules of compound (I) show a short intramolecular N_Ala—H?N_exo hydrogen bond [N?N 2.661 (3) Å] and are linked into a chain along the c axis by N_endo—H?S_endo and N_endo—H?O_Ala hydrogen bonds [N?S 3.236 (3) and N?O 3.375 (3) Å] between neighbouring mol­ecules. In compound (II), the mol­ecules are connected antiparallel into a chain along the a axis by N_exo—H?O_Ala and N_Ala—H?N_endo hydrogen bonds [N?O 2.907 (6) and N?N 2.911 (6) Å]. The mol­ecules of compound (III) are dimerized antiparallel through N_exo—H?N_endo hydrogen bonds [N?N 2.956 (7) and 2.983 (7) Å]. The different hydrogen‐bonding patterns can be explained by an amido–imino tautomerism (prototropic shift) shown by different bond lengths within the 6H‐1,3,4‐thia­diazine moiety.     

On the Effect of Tether Composition on cis/trans Selectivity in Intramolecular Diels–Alder Reactions

Intramolecular Diels–Alder (IMDA) transition structures (TSs) and energies have been computed at the B3LYP/6‐31+G(d) and CBS‐QB3 levels of theory for a series of 1,3,8‐nonatrienes, H₂C?CH? CH?CH? CH₂? X? Z? CH?CH₂ [? X? Z? =? CH₂? CH₂? ( 1 ); ? O? C(?O)? ( 2 ); ? CH₂? C(?O)? ( 3 ); ? O? CH₂? ( 4 ); ? NH? C(?O)? ( 5 ); ? S? C(?O)? ( 6 ); ? O? C(?S)? ( 7 ); ? NH? C(?S)? ( 8 ); ? S? C(?S)? ( 9 )]. For each system studied ( 1 – 9 ), cis‐ and trans‐TS isomers, corresponding, respectively, to endo‐ and exo‐positioning of the ? C? X? Z? tether with respect to the diene, have been located and their relative energies (E_rel^TS) employed to predict the cis/trans IMDA product ratio. Although the E_rel^TS values are modest (typically <3 kJ mol^?1), they follow a clear and systematic trend. Specifically, as the electronegativity of the tether group X is reduced (X?O→NH or S), the IMDA cis stereoselectivity diminishes. The predicted stereochemical reaction preferences are explained in terms of two opposing effects operating in the cis‐TS, namely (1) unfavorable torsional (eclipsing) strain about the C4? C5 bond, that is caused by the ? C? X? C(?Y)? group’s strong tendency to maintain local planarity; and (2) attractive electrostatic and secondary orbital interactions between the endo‐(thio)carbonyl group, C?Y, and the diene. The former interaction predominates when X is weakly electronegative (X?N, S), while the latter is dominant when X is more strongly electronegative (X?O), or a methylene group (X?CH₂) which increases tether flexibility. These predictions hold up to experimental scrutiny, with synthetic IMDA reactions of 1 , 2 , 3 , and 4 (published work) and 5 , 6 , and 8 (this work) delivering ratios close to those calculated. The reactions of thiolacrylate 5 and thioamide 8 represent the first examples of IMDA reactions with tethers of these types. Our results point to strategies for designing tethers, which lead to improved cis/trans‐selectivities in IMDAs that are normally only weakly selective. Experimental verification of the validity of this claim comes in the form of fumaramide 14 , which undergoes a more trans‐selective IMDA reaction than the corresponding ester tethered precursor 13 .     

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.     

Solid-State Confinement Effects in Selective exo-H/D Exchange in the Rhodium σ-Norbornane Complex [(Cy2PCH2CH2PCy2)Rh(η2:η2-C7H12)][BArF4]

Density functional theory calculations modelling selective exo-H/D exchange observed in the Rh σ-alkane complex [(Cy₂PCH₂CH₂PCy₂)Rh(η²:η²-endo-NBA)][BAr^F₄], [1-NBA][BAr^F ₄ ] , are reported, where Ar^F=3,5-C₆H₃(CF₃)₂ and NBA=norbornane, C₇H₁₂. Two models were considered 1) an isolated molecular cation, [1-NBA]⁺ and 2) a full model in which [1-NBA][BAr^F ₄ ] is treated in the solid state through periodic DFT. After an initial endo-exo rearrangement, both models predict H/D exchange to proceed through D₂ addition and oxidative cleavage followed by a rate-limiting C−H activation of the norbornane through a σ-CAM step to form a [1-Rh(D)(η²-HD)(norbornyl)]⁺ intermediate. HD rotation followed by a σ-CAM C−D bond formation, HD reductive coupling and HD loss then complete the H/D exchange process. exo-H/D exchange is facilitated by a supporting agostic interaction and is consistently more accessible kinetically than the potentially competing endo-H/D exchange (isolated cation: ΔG^≠_exo=+15.9 kcal/mol, ΔG^≠_endo=+18.4 kcal/mol; solid state: ΔG^≠_exo=+22.1 kcal/mol, ΔG^≠_endo=+25.1 kcal/mol). The solid-state environment has a significant impact on the computed energetics, with barriers increasing by ca. 7 kcal/mol, while only the solid-state model correctly predicts the endo-bound NBA complex to be the resting state of the system. These outcomes reflect solid-state confinement effects within the pocket occupied by the [1-NBA]⁺ cation and defined by the pseudo-octahedral array of neighbouring [BAr^F₄]⁻ anions. The asymmetry of the solid-state environment also requires a second H/D exchange pathway to be defined to account for reaction at all four exo-C−H bonds. These entail slightly higher barriers (ΔG^≠_exo= +24.8 kcal/mol, ΔG^≠_endo=+27.5 kcal/mol) but retain a distinct preference for exo- over endo-H/D exchange.     

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.     

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 .