Face Selectivity of the Diels-Alder Reaction of Hexadienone Moieties Grafted onto the Bicyclo[2.2.2]octene Skeleton and Perturbed by a Remote Tricarbonylbutadieneiron Group

Selective oxidations of bis(tricarbonyliron) complexes of methyl (3,7,8-trimethylidenebicyclo[2.2.2]oct-5-en-2-ylidene)methyl ketones 15 – 17 afforded selectively the tricarbonyl {(1RS,4SR,7SR,8RS)-C,7,8,C-η-[methyl (3,7,8-trimethylidenebicyclo[2.2.2]oct-5-en-(2Z)-2-ylidene)methyl ketone]}iron ( 12 ), the corresponding (2E)-derivative 13 and the tricarbonyl{(1RS,2RS,3SR,4SR)-C,2,3,C-η-[methyl (3,7,8-trimethylidenebicyclo[2.2.2]oct-5-en-(2Z)-2-ylidene)methyl ketone]}iron ( 18 ). The stereoselectivity of the Diels-Alder reactions of the uncomplexed (Z)- and (E)-hexadienone 12 and 13 , respectively, was established. The face of the diene syn with respect to the C(5), C(6) etheno bridge was preferred for the cycloadditions of N-phenyltriazolinedione (NPTAD). In contrast, the reactions of dimethyl acetylenedicarboxylate (DMAD) and methyl propynoate showed a slight preference for addtion to the face of the hexadienones anti with respect to the etheno bridges of 12 and 13 . The crystal structure of the adduct 25 resulting from the cycloaddition of NPTAD to 12 is reported.     

Synthesis and Diels-Alder Reactivity of 5,6,7,8-Tetramethylidene-2-bicyclo[2.2.2]octanol and -octanone. Selective Oxidations of the Corresponding Bis(irontricarbonyl) Complexes

Hydroboration of the syn, anti-[Fe(CO)₃]₂ double complex 24 of the readily available 5,6,7,8-tetramethylidene-2-bicyclo[2.2.2]octene ( 22 ) gave the corresponding doubly complexed 2-bicyclo[2.2.2]octanol 25. CrO₃-oxidation furnished ketone 27 . The syn-Fe(CO)₃-groups in 25 and 27 were oxidized selectively with trimethyl-amine oxide and yielded the corresponding anti-Fe(CO₃)-monocomplexed tetraenes 26 and 28. The anti-Fe(CO)₃-group in 28 could be removed, and 5,6,7,8-tetramethylidene-2-bicyclo[2.2.2]octanone ( 11 ) was obtained. NaBH₄-reduction of 11 afforded tetraenol 10. TCE-cycloadditions to 10 and 11 (k₁) were at least 10 times as fast as those (k₂) to the corresponding monoadducts 35/36 and 34 , respectively. This Diels-Alder reactivity difference vanishes (k₁ ≈ k₂) with methyl propynoate. The latter dienophile added to the anti-Fe(CO)₃-monocomplexed tetraenone 28 with ‘para’-regioselectivity.     

Circular Dichroism of Tricarbonyl(diene)iron Complexes. The Octant Rule Applied to Ketones Perturbed by Remote Fe(CO)3 Groups. Crystal Structure of (±)-Tricarbonyl[(1RS,4RS,5RS,6SR)-C5,6,C-η-(5,6,7,8-tetramethylidene-2-bicyclo[2.2.2]octanone)]iron

The preparation and the CD spectra of optically pure (+)-trans-μ-[(1R,4S,5S,6R,7R,8S)-C,5,6,C -η : C,7,8,C-η-(5,6,7,8-tetramethylidene-2-bicyclo [2.2.2]octanone)]bis(tricarbonyliron) ((+)- 7 ) and (+)-tricarbonyl[(1S,4S,5S,6R)-C-5,6,C-η-(5,6,7,8,-tetramethylidene-2-bicyclo[2.2.2]octanone)]iron ((+)- 8 ), and of its 3-deuterated derivatives (+)-trans-μ-[(1R,3R,4S,5S,6R,7R,8S)-C,5,6,C-η : C,7,8,C-η-5,6,7,8-tetramethylidene(3-D)-2-bicyclo[2.2.2]-(octanone)]bis(tricarbonyliron) ((+)- 11 ) and (+)-tricarbonyl[(1S,3R,4S,5S,6R)-C-5,6,C- η-(5,6,7,8-tetramethylidene(3-D)-2-bicyclo[2.2.2]octanone)]iron ((+)- 12 ) are reported. The chirality in (+)- 7 and (+)- 8 is due to the Fe(CO)₃ moieties uniquely. The signs of the Cotton effects observed for (+)- 7 and (+)- 8 obey the octant rule (ketone n→π*_CO transition). Optically pure (?)-3R-5,6,7,8-tetramethylidene(3-D)-2-bicyclo[2.2.2]octanone ((?)- 10 ) was prepared. Its CD spectrum showed an ‘anti-octant’ behaviour for the ketone n→π*_CO transition of the deuterium substituent. The CD spectra of the alcoholic derivatives (?)-trans-μ-[(1R,2R,4S, 5S,6R,7R,8S)-C,5,6,C-η : C,7,8,C- η-(5,6,7,8-tetramethylidene-2-bicyclo[2.2.2]octanol)]bis(tricarbonyliron) ((?)- 2 ) and (?)-tricarbonyl- [(1S,2R,4S,5S,6R)- C,5,6,C- η-(5,6,7,8-tetramethylidene-2-bicyclo[2.2.2]octanol)]iron ((?)- 3 ) and of the 3-denterated derivatives (?)- 5 and (?)- 6 are also reported. The CD spectra of the complexes (?)- 2 , (?)- 3 , (+)- 7 , and (+)- 8 were solvent and temperature dependent. The ‘endo’-configuration of the Fe(CO)₃ moiety in (±)- 8 was established by single-crystal X-ray diffraction.     

13C- and 1H-NMR. Studies on the Configuration of Tricarbonyliron Complexes of Oxa- and Aza[4.4.3]propellanes

The configurations of a series of mono- and bis-Fe(CO)₃ complexes of 12-oxa[4.4.3]-propella-2,4,7,9-tetraene ( 1 ) and of 11,13-dioxo-12-methyl-12-aza[4.4.3]propella-2,4,7,9-tetraene ( 7 ) as well as of a trienic aza-propellane complex have been studied in solution by ₁₃C- and ₁H-NMR. spectroscopy. Praseodymium-induced ₁₃C-shifts of the metalcarbonyl carbon atoms and of the central carbon atom of the complexed diene systems are particularly sensitive and useful to prove exo- or endo-configuration of the tricarbonyliron ligand. In addition, H,H- and C,H-coupling constants of the complexes and parent compounds are reported and discussed.     

Stereospecific synthesis of a dl-gala-aminoquercitol derivative

A new aminoquercitol derivative was synthesized starting from 1,4-cyclohexadiene. Photooxygenation of cyclohexa-1,4-diene afforded anti-2,3-dioxabicyclo[2.2.2]oct-7-en-5-yl hydroperoxide as the main product. The formed hydroperoxy endoperoxide was reduced with LiAlH₄ to produce anti-2,3-dioxabicyclo[2.2.2]oct-7-en-5-ol. Protection of alcohol with acetyl chloride followed by reduction of the endoperoxide with thiourea, and then palladium-catalyzed ionization/cyclization reaction gave an oxazolidinone derivative. Hydrolysis of the oxazolidinone ring and acetylation gave an amino compound. Oxidation of the double bond in the amino compound with OsO₄ followed by acetylation gave the amino tetraacetate and removal of the acetate groups furnished the desired aminoquercitol whose exact configuration was determined by X-ray diffraction analysis.     

Preparation and Diels-Alder Reactivity of Tricarbonyliron Complexes of [2.2.2]Hericene

Treatment of [2.2.2]hericene 10 with Fe₂(CO)₉ in hexane gave a mixture of monometallic complex 14 , two isomeric dimetallic complexes 15 and 16 , and a trimetallic complex 19 in which all the three diene moieties of 10 , are coordinated. The rate constants of the Diels-Alder additions of tetracyanoethylene (TCE) and dimethyl acetylenedicarboxylate (DMAD) to the uncomplexed diene moieties of 14–16 have been evaluated and compared with those measured for the uncomplexed 10 and its monoadducts 11A, 11B and bis-adducts 12A, 12B. The tricarbonyldieneiron function retards the cycloaddition of an homoconjugated, exocyclic s-cis-butadiene. The effect is significantly larger for TCE- than for DMAD-additions. The origin of this effect is discussed briefly in terms of the valence-bond model which is usually assumed to describe the properties of a tricarbonyldieneiron complex, and in terms of the inductive and steric factors of the Fe(CO)₃-group.     

Heterogenous Oxidation of [2.2.1] Bridged Bicyclic Alkenes with KMnO4-CuSO4.5H2O: An Alternative Ozonolysis

Seven [2.2.1] bridged alkenes were cleaved to the corresponding dialdehyde products by neutral heterogenous oxidation with KMnO₄-CuSO₄.5H₂O. While endo, endo-dimethyl bicyclo[2.2.2]oct-5-ene-2,3-dicarboxylate, [2.2.2] bridged alkene, gave the corresponding α-hydroxy ketone, endo, endo-dimethyl bicyclo[3.2.2]non-8-ene-6,7-dicarboxylate afforded a diketone product.     

19F substituent chemical shifts (SCS) of 4-substituted bicyclo[2.2.2]oct-1-yl flourides

The results of a linear multiple regression analysis indicate that the ¹⁹F SCS of 4-substituted bicyclo[2.2.2]oct-1-yl fluorides are essentially a manifestation of electric field and electronegativity effects.     

Long-range deuterium isotope effects on fluorine-19 chemical shifts of 4-substituted bicyclo[2.2.2]octyl- and bicyclo[2.2.1]heptyl-1-fluorides : Deuterium as a substituent

²H/¹H isotope effects on the ¹⁹F chemical shifts of 4-substituted bicyclo[2.2.2]oct-1-yl and bicyclo[2.2.1]hept-1-yl fluoride are significantly shielding and deshielding, respectively. This result is consistent with deuterium being viewed as an $\text{electronegative}$ substituent relative to hydrogen when attached to an sp³ hybridised carbon.     

Face Selectivity of the Diels-Alder Additions of 2-Substituted 5,6-bis((E)-chloromethylidene)bicyclo[2.2.2]octanes

The preparation of 5,6-bis((E)-chlorommethylidene)bicyclo[2.2.2]oct-2-ene ( 13 ), 2,3-bis((E)-chloromethyl idene)-5exo,6exo- and -5endo,6endo-epoxybicyclo[2.2.2] octane ( 14 and 15 ), 5,6-bis((E)-chloromethylidene)-2exo- and -2endo-bicyclo[2.2.2] octanol ( 16 and 17 ) and 5,6-bis((E)-chloromethylidene)-2-bicyclo[2.2.2]octanone ( 18 ) are described. The face selectivity (endo-face vs. exo-face attack onto the exo-cyclic diene) of their cycloadditions to tetracyanoethylene has been determined in benzene at 20°. It is 78/22, 80/20, 60/40, 68/32, 3/97 and 30/70 for 13 , 14 , 15 , 16 , 17 and 18 , respectively.     

Die Synthese von 4-substituierten Bicyclo[2.2.2]oct-1-yl-p-nitrobenzolsulfonaten

Synthesis of 4-Substituted Bicyclo[2.2.2]oct-1-yl-p-Nitrobenzenesulfonates The syntheses of the 4-substituted bicyclo[2.2.2]oct-1-yl-p-nitrobenzenesulfonates 1a–2s are described.     

Structure of Tricarbonyl(diene)iron Complexes in Solution. Variable-Temperature Circular Dichroism of trans-μ-(2,3,5,6-Tetramethylidenebicyclo[2.2.2]octane)bis(tricarbonyliron) Complexes

Optically pure (?)-trans-μ-[(1R,2R,3S,4S,5S,6R)-C,2,3,C-η:C,5,6,C-η-(2,3,5,6,7-pentamethylidenebicyclo[2.2.2]octane)]bis(tricarbonyliron) ((?)- 9 ), (?)-trans-μ-[(1R,2R,3S,4S,5S,6R,7S)-C,2,3,C-η:C,5,6,C-η-(7-methyl-2,3,5,6-tetramethylidenebicyclo[2.2.2]octane)]bis(tricarbonyliron) ((?)- 10 ), and (?)-trans-μ-[(1R,2R,3S,4S,5S,6R,7R)-C,2,3,C-η:C,5,6,C-η-(2,3,5,6-tetramethylidene(7D)bicyclo[2.2.2]octane)]bis(tricarbonyliron) ((?)- 16 ) have been prepared. Their CD spectra were solvent- and concentration-independent, but temperature-dependent, in accord with the existence of equilibria between rapidly interconverting diastereoisomeric species which can be interpreted as arising from distortions of the tricarbonyl(diene)iron units from the C_s symmetry.     

Transition Metal Cation Salts in Organic Synthesis

Reaction of lithium diisopropylamide (LDA) with (η⁴-1,3-cyclohexadiene)Fe(CO)₃ complexes bearing functionalized side chains at C-5, under an atmosphere of carbon monoxide, gives bridged bicyclo[3,2,1]octene and bicyclo[3,3,1]nonene systems after electrophilic quenching. Under the same reaction conditions, intramolecular cyclization of acyclic (η⁴- 1,3-butadiene)Fe(CO)₃ complexes with functionalized side chains at the terminal position of the diene ligands furnishes fused bicyclo[3.3,0]octanone and bicyclo[4.3.0]nonanone derivatives after acid quenching. The addition of a variety of the highly functionalized zinc-copper reagents RCu(CN)ZnI to the (η⁷-cycloheptatrienyl)Cr(CO) gives (η⁶-cyclohepta-1,3,5-triene)Cr(CO)₃ complexes with a functionalized side-chain at the C-7 position of the ring. Intramolecular cyclization of ester-subsbtuted adducts using lithium diisopropylamide generates fused bicyclo[5.3.0]decane and bicyclo[5.4.0]undecane derivatives. The addition of a variety of the highly functionalized zinc-copper reagents RCu(CN)Znl to the (η⁴-cyclohexa-1,3-diene)Mo(CO)₂(Cp) at the terminus of the coordinated diene ligand gives [Mo(π-allyl)(CO)₂(Cp)](Cp = cyclopentadienyl) complexes with the functionalized side-chain at the C-4 position of the ring. Intramolecular cyclization of the (π-allyl)molybdenum complex containing a pendant propanoic acid unit generates the δ-lactone derivative.     

Synthetic study of optically active and C2-symmetric novel ligand, 7,8-bis(benzyloxy)bicyclo[2.2.2]octa-2,5-diene and a tricarbonyliron complex

The 7,8-bis(benzyloxy)bicyclo[2.2.2]octa-2,5-diene derivatives have been synthesized via Diels-Alder reaction of optically active 5,6-bis(benzyloxy)cyclohexa-1,3-diene and dienophiles. The corresponding tricarbonyliron complexes have also been synthesized in enantiomerically pure form.     

Iron and molybdenum carbonyls of 5,6,7,8-tetramethylenebicyclo[2.2.2]-oct-2-ene

The reaction of the title ligand with iron carbonyls under various conditions gives (tetrahapto)5,6,7,8-tetramethylenebicyclo[2.2.2]oct-2-ene-exotricarbonyliron (I) and the bis(tetrahapto)endoexo-(II) and diexohexacarbonyl diiron (III) complexes as main products. The monoexo complex reacts with Mo(CO)₃(CH₃CN)₃ giving a (tetrahapto)iron(hexahapto)molybdenum complex (IV).     

1,5-Dihydropyrrol-2-ones from (1,4-diaza-1,3-diene)tricarbonyliron and alkyne: III. Stereospecific ligand incorporation on formation of the [2.2.2]-Bicyclic intermediate

Examples of the [2.2.2.]-bicyclic intermediate formed in the reaction of (1,4-diaza-1,3-diene)tricarbonyliron complexes, (dad)Fe(CO)₃, with dimethyl acetylenedicarboxylate and an additional ligand L [L = ¹³CO, P(OMe)₃] have been isolated and characterized by elemental analysis, field desorption mass spectrometry and NMR (¹H, ¹³C, ³¹P) and IR spectroscopy. The ligand L which completes the octahedral coordination around the bridge head iron atom, is incorporated stereospecifically trans to the inserted carbonyl group of the [2.2.2] system. This is found to be the case with complexes of diazadienes of differing donor/acceptor abilities and also for the two electronically different ligands L. From the results it is concluded that a stereochemically rigid intermediate is initially formed, which for steric reasons and so in a kinetically controlled reaction, allows access of L to the iron from only one direction, consequently closing the [2.2.2] structure. Conclusive evidence that the reaction is kinetically controlled is provided by the isolation of two isomeric complexes (2b and 7, respectively) from the reactions of (dad)Fe(CO)₃ in the presence of P(OMe)₃, and of (dad)Fe[P(OMe)₃](CO)₂ from reaction in the presence of CO.     

Differential Bridging in the Solvolysis of Epimeric Bicyclic Sulfonates,Norbornanes, Part 17

The solvolysis rates and products of the 2-exo- norbornyl, bicyclo[3.2.1]oct-8-yl, bicyclo[3.3.1]non-2-yl, bicyclo[3.2.1]oct-6-yl, bicyclo[3.2.1]oct-2-yl and bicyclo[3.2.2]non-6-yl p-toluenesulfonates 10–15 , respectively, are reported. The exo/endo rate ratios for these epimeric secondary tosylates in 80% EtOH varied from 1125 for 11 to 1.6 for 15 . The relative rates varied between 2278 for exo- 10 and 4 ·10^?3 for endo- 11 . The hydrolysis products were mainly rearranged alcohols and olefins. The unrearranged alcohols from the exo-tosylates were formed with complete or predominant retention of configuration, whereas those derived from the endo-tosylates were mostly inverted. These results confirm the hypothesis that relative rates, as well as products, are largely determined by the degree of bridging between the cationic center and a dorsal C-atom in the transition state and in the resulting ion pairs. Since bridging is a directed bonding interaction, it is subject to the same angle and conformational strains as ordinary covalent bonds. But bridging requires less geometrical change than the formation of normal bonds and of nonclassical ions.     

Kinetics and mechanism of the thermal reactions of endo- and exo-5-cyanobicyclo[2.2.2]oct-2-ene and methyl-substituted derivatives in the gas phase

The thermal reactions of endo- and exo-5-cyanobicyclo-[2.2.2]oct-2-ene and their trans- and cis-6-methyl-substituted derivatives have been investigated in the gas phase between 518 and 630 K. Each product decomposes by two parallel first-order retro-Diels-Alder reactions, a main one with formation of cyclohexa-1,3-diene and a minor one with elimination of ethene. Slight isomerizations are also observed. The kinetic results can be explained in terms of a biradical mechanism. The rate-determining step is shown to depend on the amount of resonance energy in the biradical. Heats of formation and entropies of the bicyclo[2.2.2]oct-2-enes studied are estimated.     

Thermotropic copolyesters. II. Synthesis and characterization of copolyesters containing the bicyclo[2.2.2]oct-2-ene mesogenic unit

Random copolyesters based on 1,4-benzenedimethanol, trans-1,4-cyclohexanedimethanol, and 1,4-bicyclo[2.2.2]octanedimethanol as spacers in ratios of 2 : 3 of the mesogenic group, bicyclo[2.2.2]oct-2-ene-1,4-diol were prepared and characterized. The copolyesters containing the 1,4-benzenedimethanol moiety formed a more brightly colored birefringent fluid in the melt.     

The first carbonyl iron complexes with dihydroacepentalene ligands

1,4-Dibromo- (8) as well as 1,4,7-trichloro- (11a) and 1,4,7-tribromotriquinacene (11b) react with Fe₂(CO)₉ in THF to yield (dihydroacepentalene)hexacarbonyldiiron complexes 9 and 10, the first representatives with a 7,10-dihydroacepentalene ligand. By reaction with Fe₂(CO)₉, the readily accessible 4,7-bis (dialkylamino)tricyclo[5.2.1.0^4.10]deca-1(10),2,5,8-tetraenes 14, derivatives of the unknown 4,7-dihydroacepentalene, were transfomed into their tricarbonyliron complexes 15. Upon reduction with sodium in THF, the η⁴-(diene)tricarbonyliron 15 selectively gave the novel 1,10η²-(olefin)tricarbonylferrates(-2)17 as a result of a twofold electron transfer. The intermediate green radical anion 16, which is persistent in the absence of excess sodium, was characterized by its ESR signal. Complexes 17 are the first of their class with complete structural characterization by ¹H- and ¹³C-NMR spectroscopy.