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The reaction of benzyne (generated by the thermolysis of o- diazoniobenzoate) with the following alkenes has been examined: 1,1- dichloroethene (5) (vinylidene chloride), 1,1-dichloro-propene (7), 1,1-dichloro-2-methylpropene (17), 2-methylprop-1-en-1-yl acetate (18) and 2-chloro-prop-2-enenitrile (α-chloroacrylonitrile) (22). Substituted bicyclo[4,2,0]octa-1,3,5-trienes resulting from 2+2 cycloaddition were obtained from (5), (7), and (22), while the reaction involving the en01 acetate (18) gave only ?ene? product, and that involving (17) gave an intractable mixture. (Z)- and (E)-1-Chloro-2-(o- chlorophenyl)propene were obtained as minor products in the reaction of benzyne with (7): these products result from a chlorine atom transfer to the aromatic ring, and a novel mechanism involving a diradical → carbene rearrangement is postulated.

The compounds (1,7,8,9-η-bicyclo[5,2,0]nonatetraenyl hexafluorophosphate)tricarbonyliron (9), (1,7,8,9-η-bicyclo[5,2,0]nona- 1(7),2,5,8-tetraen-4-one)tricarbonyliron (10), and (1,7,8,9-η-bicyclo- [5,2,0]nona-1(7),3,5,8-tetraen-2-one)tricarbonyliron (11) have been prepared. The cation (9) undergoes nucleophilic capture at C2, the position α to the coordinated cyclobutadiene ring. Oxidative removal of the tricarbonyliron group from the symmetrical tropone derivative (10) generates bicyclo-[5,2,0]nona-1(7),2,5,8-tetraen-4-one, which can be trapped as a Diels-Alder adduct with cyclopentadiene.

Synthetic routes to 5H-benzo[3,4]cyclobuta[1,2]cyclohepten-5-one (6), 6H-benzo[3,4]cyclobuta-[1,2]cyclohepten-6-one (5) and 7H- benzo[3,4]cyclobuta[1,2]cyclohepten-7-one (7), which are analogues of biphenylene in which one benzenoid ring has been replaced by the cyclohepta-2,4,6-trienone (tropone) ring, have been investigated. The tropone (5) was obtained as a stable, crystalline solid and 1H n.m.r, evidence suggests that (5) has a more localized π-bond system in the seven-membered ring than tropone itself. The reactive tropone derivative (7) was generated in solution, and trapped as a 6πs+4πs cycloadduct with cyclopentadiene.

The title cation (5), which is an analogue of biphenylene in which one of the benzenoid rings has been replaced by a cycloheptatrienyl ion (tropylium) ring, has been prepared by hydride ion abstraction from 6H- benzo[3,4]cyclobuta[1,2]cycloheptene (19) (?homobiphenylene?). The compound (19) was obtained by a sequence of brominations and dehydrobrominations from 5,6,7,8,9,9a-hexahydro-4bH- benzo[3,4]cyclobuta[1,2]cycloheptene (13). N.m.r. spectroscopy indicates that the cation (5) is best considered as possessing two essentially independent 6π electron systems. Nucleophilic capture of cation (5) by methoxide ion yields 9-methoxyfluorene, instead of the predicted product, 4b-methoxy-4bH-benzo[3,4]cyclobuta[1,2]cycloheptene. This rearrangement of derivatives of 4bH- benzo[3,4]cyclobuta[1,2]cycloheptene to derivatives of fluorene appears to be a general reaction, and mechanistic aspects of this interesting transformation are discussed.

The crystal structure of the title compound, [Fe(CO)4(C10H8O)], has been determined at 295 K from diffractometer data, and refined by least squares to a residual of 0.073 for 2990 ?observed? reflections. Crystals are triclinic, Pī, a 22.980(6), b 9.385(3), c 6.313(2) Ǻ, α 85.22(3), β 87.67(3), γ 79.48(3), Z4. The two independent molecules in the same cell differ only trivially in their geometries, the coordination number about the metal being essentially five: four carbonyls and the ethylene double bond in a pseudo-trigonal-bipyramidal arrangement. From distortions observed within the molecular geometry as a result of steric interactions between the epoxide oxygen and the nearby axial carbonyl, it clearly emerges that the stability of the present derivative relative to that of methylene bridged ligands is simply a consequence of the greatly increased stereochemical interaction of the latter and not of any electronic effect.

Dimethyl 1,2,2a,10b-tetrahydrocyclobuta[l]phenantene-cis-1,2- dicarboxylate has been converted into 8b,8c,9,11,11a,11b- hexahydrophenanthro[9?,10?:3,4]cyclobuta[1,2-c]furan (9) and 8c,9,11,11a-tetrahydrophenanthro[9?,10?:3,4]cyclobuta[1,2-c]furan (5) by a series of standard reactions. Bromination of (9) with N- bromosuccinimide gave 3-bromo-4-(9?-phenanthryl)tetrahydrofuran (14) by an unusual fragmentation of the cyclobutyl ring. Reaction of (5) with N-bromosuccinimide resulted in the introduction of the N-succinimyl substituents into the α-position of the tetrahydrofuran ring.

In contrast to the normal addition mode of hexachlorocyclopentadiene (3) to norbornadiene, which yields mainly (but not exclusively) aldrin having the endo-exo-1,4:5,8-dimethanonaphthalene skeleton, the reaction of (3) with norbornadien-7-yl acetate gives three adducts: 1,2,3,4,10,10-hexachloro-1,4,4a,5,8,8a-hexahydro-endo-endo-1,4:5,8-dimethanonaphthalen-syn-9-yl and -anti-9-yl acetates [(7) and (9)] and the 'normal' 1,2,3,4,10,10-hexachloro-1,4,4a,5,8,8a-hexahydro-endo-exo-1,4:5,8-dimethanonaphthalen-syn-9-yl acetate (11). The addition of (3) to 7-t-butoxynorbornadiene yields mainly the anti-9-t-butoxy-endo-endo adduct, analogous to (9), while the addition of (3) to 7-methylnorbornadiene gives mainly syn-9-methyl-endo-exo-adduct,analogous to (11). The structure of these adducts has been determined by spectroscopic (N.M.R. and infrared) and chemical (photochemicalcyclization of the endo-endo systems) means.

Syntheses of exo- and endo-tricyclo[6,2,1,02,7]undeca-3,5,9-triene, (3) and (4) respectively, are described. Both trienes undergo ready π4s+ π28 cycloreversion to yield cyclopentadiene and benzene at 40-60C, the exo-triene (3) being slightly more reactive. At 60C, for (3) k = 2.29x 10-3 s-1, ΔH? = 104.1 4.2kJ mol-1, ΔS? =14.6 1.6 mol-1 K-1, while for (4) k = 5.25 x 10-3s-1, ΔH? =ll5.0 3.3 kJ mol-1, ΔS? = 34.3 13.0 J mol-1 K-1 . The cycloreversion of (3) and (4) are believed to be concerted reactions. The related dienes exo- and endo-tricyclo[6,2,1,02,7]undeca-3,5-diene, (25) and (28) respectively, have also been prepared, and are stable up to 200C. At 300C, interconversion between (25) and (28) occurs, apparently via bicyclo[6,2,1]undeca-2,4,6-triene. The relationship of the trienes (3) and (4) to the recently described bicyclo[6,2,l]undeca-2,4,6,9-tetraene is discussed.

Reaction of 1,2,3,4-tetrachloro-5,5-dimethoxycyclopentadiene with norbornadiene and benzo-norbornadiene gave adducts having the endo-exo-1,4,4a,5,8,8a-hexahydro-1,4:5,8-dimethano-naphthalene and endo-exo-1,4,4a,9,9a,l0-hexahydro-1,4:9,l0-dimethanoanthracene skeletons, respectively. These adducts were dechlorinated to give acetals, which were hydrolysed to give the corresponding ketones. The initial adducts, and the derived acetals and ketones, are all sterically compressed as a result of crowding of the C2-C3 etheno bridge against a methano hydrogen atom syn to that bridge. This steric compression manifests itself in a marked deshielding of the relevant methano proton in the N.M.R. spectra of these compounds, and in an increased rate of thermal decarbonylation of the ketones. The location of the deuterium atom in benzonorbornadiene[7-anti-D] (12) has been established chemically by observing an intramolecular deuterium transfer during photochemical half-cage formation from the adduct of (12) and 1,2,3,4-tetrachloro-5,5- dimethoxycyclopentadiene.

A series of 3-alkoxyanthranilic acids, in which a furan ring is attached to the terminal carbon atom of the alkoxy group, has been prepared. When the chain linking the anthranilic acid and furan ring systems is three or four atoms long, decomposition of the derived diazonium chlorides generates the corresponding benzynes , which are efficiently trapped intramolecularly by the furan moiety. Diazotization of 2-amino-3-furfuryloxybenzoic acid, where the linking chain is two atoms long, results in fragmentation with the formation of 6-diazo-5- oxocyclohexa-1,3-diene-1-carboxylic acid.

Benzynes, generated either by the debromination of an appropriately substituted (o-dibromobenzene, or by the thermolysis of a substituted diazotized anthranilic acid, have been trapped intramolecularly by an attached furan moiety. One such adduct (41) has been transformed into 6,9-dimethylnaphtho[1,8-bc]pyran-3(2H)-one (43), which served as the key intermediate for the total synthesis of the title compounds, all of which are derivatives of 6,9-dimethylnaphtho[1,8-bc]pyran-7,8-quinone.

1,4-Epoxy-1,4-dihydroarenes are converted in high yields into the corresponding arenes with enneacarbonyldiiron in refluxing benzene solution.

The sesquiterpene ()-sinularene (exo-5-isopropyl-2-methyl-7-methylenetricyco[4,4,0,02,8]decane) has been synthesised by a 15-step sequence starting with anti-7-methylbicyclo[2,2,1]heptane-syn- 7, exo-2-carbolactone.

The acetolysis of α-campholenyl [2-(2',3',3'-trimethylcyclopent-3'-enyl)] p-nitrobenzenesulphonate proceeds with π-bond participation to give cyclized products (99.7%) derived from the equilibrating classical camphene hydro and isopropyl cations. The composition of the product is similar, but not identical, to those formed by the σ-route from the acetolysis of suitable isopropyl and bornyl derivatives. When α-campholenyl p-nitrobenzenesulphonate and the isopropyl derivatives are prepared from (+)-camphor, the two enantiomers of camphene having high optical purities are formed. A simple procedure for the preparation of camphene of high optical purity from isoborneol is described.

Reaction of benzonorbornadiene, 7-isopropylidenebenzonorbornadiene (1,4-dihydro-9-isopropylidene-1,4-methanonaphthalene) and 1,4-dihydro-1,4-epoxynaphthalene (7-oxabenzonorbornadiene) with dicarbonyldinitrosyliron, Fe(CO)2(NO)2, gave in good yields the corresponding dimers having the exo-trans-exo configuration. Treatment of a mixture of benzonorbornadiene and norbornadiene with Fe(CO)2(NO)2 gave a 'crossed dimer', in addition to the dimers derived from benzonorbornadiene and norbornadiene. The reaction of benzonorbornadiene with pentacarbonyliron at 100 gave the exo-trans-exo dimer and a ketone derived by dimerization and carbonyl insertion. This ketone, and the analogous ketone obtained from 7-isopropylidenebenzonorbornadiene, have been assigned the exo-trans-exo configuration. Reaction of 1,4-dihydro-1,4-epoxynaphthalene with enneacarbonyldiiron, Fe2(CO)9, at room temperature gave tetracarbonyl(l,4-dihydro-l,4-epoxynaphthalene)iron(0), in which the olefinic ח-bond is bonded to the metal. In solution at 63 this complex gave naphthalene.

The title reaction affords the 2+2 cycloadduct cis-4b,9b-dihydrobenzo[3,4]cyclobuta[1,2-b]benzofuran (13) together with the bis-adduct (4aα,8bα,9β,13b β)-8b,9-dihydro-9,13b-epoxy-13bH- benzo[3,4]cyclobuta[l,2-k]phenanthrene (14) in a ratio of c. 1 : 8. The mechanism of formation of these adducts is suggested to occur through a non-concerted pathway. Treatment of (14) with acid results in rearrangement and dehydration to give benz[e]acephenanthrylene in good yield.

Diels-Alder reaction between furan and α-chloroacrylonitrile gives a mixture of exo-2-chloro-and endo-2-chloro-7-oxabicyclo[2.2.1]hept-5-ene-2-carbonitrile (4) and (5). Mild hydrolysis affords the corresponding α-chloro acid mixture, from which the endo carboxylic acid may be removed through iodo lactone formation. Catalytic hydrogenation of (4) and (5) followed by hydrolysis, acyl azide formation, Curtius rearrangement, and hydrolysis of the resulting mixture of a-chloro isocyanates yields 7-oxabicyclo[2.2.l]heptan-2-one (1) in preparatively useful amounts. Reduction of (1) gives only endo alcohol, and Baeyer-Villiger reaction proceeds with exclusive bridgehead atom migration. Thermal decomposition of the sodium salt of the p-toluenesulfonylhydrazone of (1) affords 7-oxatricyclo[2.2.1 .02,6]heptane.

No Abstract Available

Benzonorbornadienone could not be isolated at 0, nor detected at -45 in the hydrolysis of 7,7-dimethoxybenzonorbornadiene (9,9-dimethoxy- 1,4-dihydro-1,4-methanonaphthalene) (5). Reaction of (5) with chromium hexacarbonyl gave endo-tricarbonyl(7,7- dimethoxybenzonorbornadiene)chromium (14) (1 %) and a new type of alkene-ether complex of composition (7,7- dimethoxybenzonorbornadiene)-Cr(CO)4 (36%). Hydrolysis of (14) gave-only tetracarbonyl(naphthal-ene)chromium (24), and naphthalene. Oxidation of exo- and endo- tricarbonyl(anti-7-benzonorbornadienol)chromium with silver carbonate on Celite at 40 gave mainly tricarbonyl(1-naphthaldehyde)chromium, accompanied by a small amount of (24). It is concluded that benzonorbornadienone and tricarbonyl(benzonorbornadienone)chromium are unstable at -45, and 40, respectively. The factors contributing to the instability of these ketones are briefly discussed.