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The arylmethylidenecyclopropa[b]naphthalene family has been extended to include the 1and 2naphthyl and 9-anthryl derivatives (5-7). When subjected to Ag(I) in aprotic media, conditions typically employed for the linear dimerization of the parent cycloproparenes, diarylalkynes and/ or ketones are obtained; in alcoholic media enol ethers are formed. Dimerization to 9,10-anthraquinodimethanes does not take place.

The first simple and stable cross-conjugated π-extended alkylidenecycloproparenes 5, 6 and 15−22 have been prepared as coloured crystalline derivatives from use of (E,E)-1,5-diphenylpenta-2,4-dienone, (E,E)-1,5-diarylpenta-1,4-dien-3-ones and (E,E)-2,5-(diarylmethylidene)cyclopentanones with the relevant 1,1-bis(trimethylsilyl)cyclopropa[b]naphthalene. The permanent dipole moments of the compounds have been measured, and the conformational preference of the rotamers assessed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Dithiole and cyclopentadiene rings have been introduced into functionalised cyclopropa[b]naphthalenes to provide highly coloured, conjugated and cross-conjugated π-extended derivatives that have varying stability. Cyclopentadienylidene-containing cyclopropanaphthalene 18 and its dithiolylidene analogue 25 are prepared from bromophenylcyclopropanaphthalene 12, and the 1,1-biscyclopentadienylidene 20 from dibromide 13. Use of dithiole-containing ketones with 1,1-bis(trimethylsilyl)cyclopropa[b]naphthalene 10 gives the π-extended cycloproparenes 27 and 29 in Peterson olefinations that are more efficient than Wittig−Horner reactions of cyclopropanthraquinone 31 with dithiolate 24 to give the cross-conjugated cycloproparenes 34 and 35. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

1H-Cyclopropa[b]naphthalene-3,6-dione 3 adds bromine stoichiometrically across the enedione C=C bond to give dibromodihydrocyclopropanaphthalenedione 10 while with an excess of the reagent (bromomethyl)tribromonaphthoquinone 12 is formed. Typical quinone character is exhibited by 3 in Diels-Alder cycloadditions and it gives the endo-methanocyclopropanthraquinone 14 with cyclopentadiene. With buta-1,3-diene the analogous tetrahydrocyclopropanthraquinone 15 is formed from a temperature dependent reaction. Above 45 degrees C opening of the three-membered ring of 4 also occurs and the cyclopentanthracenedione 16 is obtained from [pi 2+pi 4] and [sigma 2+pi 2] additions; it is the sole product at 100 degrees C. Enolisation of the tetrahydroanthraquinone 15 provides diphenolate 18 and this can be diverted to diether 19 or readily oxidized to the dihydroanthraquinone 20. In turn, 20 is dehydrogenated to the fully aromatic cyclopropa[b]anthracene-3,8-dione 4, the first anthraquinone of the cycloproparene series.

Desilylation of 1,1-bis(trimethylsilyl)-1H-cyclopropa[b]naphthalene 10 with tert-butoxide or hydroxide ion gives anion 9 as a highly reactive species. Formed with tert-butoxide 9 can be intercepted by iodomethane to give the 1-methyl-1-trimethylsilyl derivative 13. With hydroxide ion and water catalytic didesilylation regenerates cyclopropanaphthalene 6 quantitatively. Formation of 9 with hydroxide ion in the presence of benzophenone, fluoren-9-one or 4-(dimethylamino)benzaldehyde provides a simple and economic route to the methylidenecyclopropanaphthalenes 11, 17 and 18. With benzaldehyde and 4-fluorobenzophenone this revised protocol (to give 19 and 12, respectively) is effective only in the presence of 18-crown-6.

Upon flash vacuum thermolysis at 750 °C fluorenylidenecyclopropa[ b ]naphthalene ( 1 ) undergoes opening of the three-membered ring and rearrangement to give a range of C 24 H 14 polycyclic aromatic hydrocarbons. Dibenz[ e . l ]- and -[ e . k ]acephenanthrylene ( 7 ) and ( 12 ), respectively, have been identified while the plausible naphth[1,2- e ]- and [2,3- e ]acephenanthrylenes ( 9 ) and ( 14 ) were not detected. With diphenylmethylidenecyclopropa[ b ]naphthalene ( 2 ) cyclodehydrogenation and rearrangement also provide C 24 H 14 polycycles; dibenz[ e . k ]acephenanthrylene ( 12 ) is identified and dibenz[ a . e ]aceanthrylene ( 15 ) is a proposed product.

[reaction: see text] The first derivative of the novel and highly strained rocketene (cyclobuta[a]cyclopropa[d]benzene) 5, namely, the C4 diphenyl-substituted exocyclic alkene 8, has been prepared in 16% overall yield as a yellow oil with properties fully consistent with its highly strained nature.

The behaviour of cyclopropabenzene (1) with 1,3-diphenylisobenzofuran ( dpibf ) is temperature dependent. Addition to the strained bridge bond of (1) gives the Diels -Alder adduct (13) in tetrahydrofuran at 20°C, but in chloroform at the same temperature the ring-expanded 5,10-epoxydibenzocycloheptene (12) is also formed. Compound (12) becomes the sole product from reaction at 30°C or higher. Cyclopropa [b]naphthalene (2) is inert to dpibf under similar conditions but provides the dimer 6,13-dihydropentacene (15). The triazoloindazole (19) results from reaction of (2) with 4-phenyl-3H-1,2,4-triazole-3,5(4H)- dione.

9,9-Dichloro-1,4-dihydro-4a,8a-methanonaphthalene (4) adds the electron-deficient dienophiles 4-phenyl-1,2,4-triazoline-3,5-dione, maleic anhydride and dimethyl acetylenedicarboxylate to the α-face to give adducts (5)-(7) respectively; the addition of the alkyne requires Lewis acid catalysis. Inverse electron-demand addition of 3,6-diphenyl-1,2,4,5-tetrazine to the monoene component of (4) in hydrophilic solvent (ethane-1,2-diol) is thwarted; the CCl2 bridge is ejected and the 1,4-dihydronaphthalene formed is captured to give (ultimately) phthalazine (16). Dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate adds to (4) to give the methanobenzophthalazine (17b).

Treatment of 6,6-dichloro-3-oxabicyclo[3.1.0]-hexane (7) with potassiumt-butoxide generates the ring-strained cyclopropene8 as a reactive intermediate. With 1,3-diphenylisobenzofuran compound8 is trapped as a ∼5∶1 mixture of theexo- andendo-adducts11a and11b, respectively. With furan only the ring expanded vinylcarbene12 is intercepted and spirocycle13a is formed. Carbene12 is also captured by cyclohexene, 2,3-dihydrofuran, 2,5-dihydrofuran, and diphenylethyne to give22–25 respectively. A likely side product in these reactions is the pyran14.

The reactions of halogenated [n.m.1]propellenes with potassium t-butoxide have been investigated. Propelladiene 9,9-dichloro-1,4,5,8-tetrahydro-4a,8a-methanonaphthalene affords 1,6-methano[10]-annulene, 4-methylazulene, and 5H-benzocycloheptene, while the related tetracyclic compound-1,1,8,8-tritrachloro-1a,2,3,6,7,7a-hexahydro-2a,6a-methano-1H-cyclopropa[b]naphthalene reacts to give 12-chlorotricyclo[5.4.1.03,5]dodeca-1,3(5),6,8,10-pentaene. Treatment of 8,8-dichloro-2,3,4,7-tetrahydro-3a,7a-methano-1H-indene with the same base produced a mixture of the chlorodiene 8-chloro-2,3-dihydro-3a,7a-methano-1H-indene, azulene, and 4-methylazulene. The structure of the chlorodiene was established by an X-ray crystallographic study of its Diels–Alder adduct with 4-phenyl-4H-1,2,4-triazole-3,5-dione. While reaction of tetracycle 1,1,syn-8-trichloro-1 a,2,3,6,7,7a-hexahydro-2a,6a-methano-1H-cyclopropa[b]naphthalene with base failed to produce any characterisable products, under the same conditions epimer 1,1,anti-8-trichloro-1a,2,3,6,7,7a-hexahydro-2a,6a-methano-1H-cyclopropa [b] naphthalene was converted into the cycloproparene tricyclo-[5.4.1.03,5]dodecs-1,3(5),6,8,10-pentaene. Mechanistic proposals which account for the observed conversions have been advanced and are supported by 13C-labelling studies. The initial steps in most of the reaction pathways of the substrates are probably 1,4-elimination processes involving abstraction of an allylic hydrogen, fragmentation of the strained propellene σ-bond, and ejection of the halogen in an endo-relationship to the abstracted proton. The primary product of these processes, bridgehead dienes such as bicyclo[4.4.1]undeca-1,3,6(11),8-tetraene, 4,4,12-trichloro-tricyclo[5.4.1.03.5]dodeca-1 (11), 7(12),9-triene. and 10-chlorobicyclo[4.3.1]deca-1,3,6(10)-triene, then undergo further reaction involving, amongst other things, 1,3-prototropic shifts. Attempts to probe the mode of formation of the C11-4-methylazulene from the C10-precursor 8,8-dichloro-2,3,4,7-tetrahydro-3a,7a-methano-1H-indene have uncovered a novel methylation reaction of azulene by the dimsyl anion.

The reactive bicyclo[n.1.0]alk-1(ω)-enes (n=3-6) 9a-d are formed by dehydrochlorination of 8a-d and trapped by diphenylisobenzofuran as exo Diels-Alder adducts 10a-d. With 8c the major adduct, 18 results not from interception of 9c but from diene 16 that is formed by dehydrochlorination/rearrangement sequences. Attempted interception of cyclopropenes 9a-d by furan provides a [4+2] product 19 from 9b (n=4) only

The reactions of diarylalkylidenecycloproparenes in [2+4] and [2+2] cycloadditions are described.

The first cyclopropa-fused anthraquinone, 1 H -cyclopropa[ b ]anthracene-3,8-dione, is available in four steps from homologation of 1 H -cyclopropa[ b ]naphthalene-3,6-dione.

The 1H-cyclopropa[b]naphthalenyl anion reacts with N,N-dimethylamides to provide C-1 acyl derivatives in good yield in what are rare examples of mono-substitution in the cycloproparene series. The availability of these acylcycloproparenes provides for subsequent benzylic proton abstraction and enolate ion interception to give O-silyl and O-phosphinate derivatives. This reaction sequence leads to the first cyclopropa[b]naphthalenylidene enol ethers and provides the only example of exocyclic alkene formation taking place in one step from the benzylic centre. Protonation of the acyl derivatives by mineral acid triggers three-membered ring opening to 2,3-disubstituted naphthalenes rather than 2-monosubstituted analogues that typically arise from protonation at the aromatic ring. Upon thermolysis ring expansion to a naphthofuran occurs.

The reactive bicyclo[n.1.0]alk-1(ω)-enes (n=3-6) 9a-d are formed by dehydrochlorination of 8a-d and trapped by diphenylisobenzofuran as exo Diels-Alder adducts 10a-d. With 8c the major adduct, 18 results not from interception of 9c but from diene 16 that is formed by dehydrochlorination/rearrangement sequences. Attempted interception of cyclopropenes 9a-d by furan provides a [4+2] product 19 from 9b (n=4) only

Treatment of 6,6-dichloro-3-oxabicyclo[3.1.0]-hexane (7) with potassiumt-butoxide generates the ring-strained cyclopropene8 as a reactive intermediate. With 1,3-diphenylisobenzofuran compound8 is trapped as a ∼5∶1 mixture of theexo- andendo-adducts11a and11b, respectively. With furan only the ring expanded vinylcarbene12 is intercepted and spirocycle13a is formed. Carbene12 is also captured by cyclohexene, 2,3-dihydrofuran, 2,5-dihydrofuran, and diphenylethyne to give22–25 respectively. A likely side product in these reactions is the pyran14.

1 H -Cyclopropa[ b ]naphthalene(V) reacts with chlorotris(triphenylphosphine)rhodium(I) and (ethene)bis(triphenylphosphine)platinum(0) with oxidative insertion of the metal into the three-membered ring σ-bond; rhodia- and platina-2 H -cyclobuta[ b ]naphthalenes result. Tetrakis(triphenylphosphine)palladium(0) provides an unstable homologous product.

Reaction of tetraphenylcyclopentadienone with (1H-cyclopropa[b]naphthalen-1-yltrimethyl)silane anion [derived by monodesilylation of 1,1-bis(trimethylsilyl)cyclopropa[b]naphthalene] gives the 1-(5'-cyclopentadienyl)substituted cycloproparene from simple anion addn. to the carbonyl group rather than fulvalene from loss of Me3SiO-. Reactions of (1H-cyclopropa[b]naphthalen-1-yltrimethyl)silane anion with p-(trifluoromethyl)benzaldehyde and thiophene-2-carboxaldehyde give the expected exocyclic olefins, 1-[[3-(trifluoromethyl)phenyl]methylene]-1H-cyclopropa[b]naphthalene and 2-(1H-cyclopropa[b]naphthalen-1-ylidenemethyl)thiophene. In contrast, 3,6-dimethoxy-1H-cyclopropa[b]naphthalen-1-yltrimethylsilane anion, obtained from a cycloproparene deriv., gives a C1 unsubstituted cycloproparene and Tishchenko products, p-(trifluoromethyl)benzyl p-(trifluoromethyl)benzoate and 2-thienylmethyl 2-thiophenecarboxylic acid 2-thienylmethyl ester.

3,6-Dimethoxy-1H- cyclopropa[b]naphthalene 4 is available from 1,4-benzoquinone in four steps in 27–28% overall yield. The diether 4 provides a range of methylidene derivatives 15a–e by way of the disilyl compound 14, and is efficiently demethylated by cerium(IV) ammonium nitrate to provide 1H-cyclopropa[b]naphthalene-3,6-dione 16 (85%) whose crystal structure is reported. Quinone 16 is the first stable cyclopropaquinone but it resists conversion into a 1-C exocyclic olefin. The chemistry of the compounds is described, their spectral data are discussed, and the cyclic voltammetry of 16 is provided.

Reaction of benzene-1,4-dicarboxaldehyde with anion 6 derived from 1,1-bis(trimethylsilyl)cyclopropa[b]naphthalene 1 gives 4-(methylidene-1H-cyclopropanaphthalenyl)benzaldehyde 7 as a minor product and 1,4-bis(methylidene-1H-cyclopropanaphthalenyl)benzene 8 as the major product of the reaction. With 4-{(E)-2-[4-(dimethylamino)phenyl]ethenyl}benzaldehyde 14, this same anion affords the stilbene-substituted π-extended (1-arylmethylidene)cyclopropanaphthalene 15 as a sparingly soluble orange-red powder.

The only charge-transfer (CT) complex formed from (p-dimethylaminophenyl)methylidene-1H-cyclopropa[b]naphthalene 7a is with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) 1 in acetonitrile. The methoxy-, thiomethyl-, and unsubstituted-phenyl analogues 7b–7d complex only with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-1,4-benzoquinodimethane (TCNQF4) 2, and then only in dichloromethane; TCNQ 3, TCNE 4, and the o-CA 5 and p-CA 6 are without effect on any of 7a–7j. In contrast, the bis(dimethylaminophenyl)methylidene homologue 9a complexes with each of 1–5 but is the only diaryl derivative to do so. The polar parent, 1H-cyclopropa[b]naphthalene, does not form a CT complex with any of the acceptors employed.

Dimethoxycarbene, generated from 2,2-dimethoxy-5,5-dimethyl-D3 -1,3,4-oxadiazoline (8), adds to the electron-deficient double bond of ring-fused cyclobutene diesters (11), (12) and (15) from the face remote from the methano bridge to give the respective bicyclo[2.1.0]pentanone acetals (13), (14) and (16). In two cases, dimethylcyclopropanes (17) and (24) also formed as by-products in these reactions. Mechanisms for the formation of all products and by-products are proposed, especially in regard to an unusual 1,3-dipolar cycloaddition product (23) isolated from the reaction of (8) with (11). Hydrolysis of acetal (13) to the ring-fused cyclopropanone (27) is thwarted by preferential release of ring strain of an external cyclopropyl carbon–carbon bond. In acid media this results in the formation of a benzonorbornane-fused cyclobutane triester (26) with proton capture from the same face, likely from concerted methoxy group-assisted opening of the three-membered ring. Kinetic product (26) is isomerized to the thermodynamic isomer (30) with sodium methoxide. Attempted deacetalization of (13) with iodotrimethylsilane gives (26) when traces of acid are present, but provides the thermodynamic product (30) directly in the presence of pyridine.

1-(Trimethylsilyl)-1H-cyclopropa[b]naphthalene (10) and its 1-methyl derivative (11) have been isolated as pure compounds from use of a lipophilic size exclusion gel. Acylation of the 1H-cyclopropa[b]naphthalenyl anion (2) is effected with N,N -dimethyl-benzamide and -acetamide to give (5) and (6), respectively. Analogous reactions with the 1-(trimethylsilyl)-1H-cyclopropa[b]naphthalenyl anion (9) do not yield the 1-acyl-1-(trimethylsilyl)-1H-cyclopropa[b]naphthalenes (12) and (13); instead the novel 6-methyl- 7H-dibenzo[b,g]fluorene (15) results from attempted acetylation. Compound (15), a formal dimer of 1H-cyclopropa[b]naphthalene (1), is formed also from anion (9) both in toluene and from addition of hydrocarbon (1); its structure is assigned from spectroscopic data and confirmed by single-crystal X-ray analysis.

Oxygen transfer from dimethyldioxiran to 1-diphenylmethylidene-1 H-cyclopropabenzene (8b) proceeds to give the corresponding epoxy derivative (7b), the simplest and most stable oxaspiropentene yet recorded. The compound has been characterized spectroscopically prior to ring expansion and rearrangement to the cyclobutenone (9b) above 20°C; this is the sole product isolated when the reaction is performed at or above room temperature. If the oxygenation reaction is performed under conditions other than strictly anhydrous, the rearrangement (7b) → (9b) competes with protonation of the oxygen atom and sequential opening of the three-membered ring to provide the hydroxyethanone (11b) via the diol (10b).

The dichloromethylene -bridged annulene (5) is available in four steps (47%) from 1,4,5,8-tetrahydronaphthalene (11) via the dibromide (15); the minor (5%) product of dehydrobromination of (15) is 2-bromo-9,9-dichloro-1,4-dihydro-4a,8a-methanonaphthalene (16). Dichlorocarbene adds to the norcaradiene form of (5) to give adduct (6) with 80% efficiency. Diene (6) resists both [π4+π2] cycloadditions and reductive dechlorination. Neither (5) nor parent 1,6-methano[10] annulene (18) adds methylene from Simmons-Smith cyclopropanation procedures.

9,9-Dichloro-1,4-dihydro-4a,8a-methanonaphthalene (4) adds the electron-deficient dienophiles 4-phenyl-1,2,4-triazoline-3,5-dione, maleic anhydride and dimethyl acetylenedicarboxylate to the α-face to give adducts (5)-(7) respectively; the addition of the alkyne requires Lewis acid catalysis. Inverse electron-demand addition of 3,6-diphenyl-1,2,4,5-tetrazine to the monoene component of (4) in hydrophilic solvent (ethane-1,2-diol) is thwarted; the CCl2 bridge is ejected and the 1,4-dihydronaphthalene formed is captured to give (ultimately) phthalazine (16). Dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate adds to (4) to give the methanobenzophthalazine (17b).

The behaviour of cyclopropabenzene (1) with 1,3-diphenylisobenzofuran ( dpibf ) is temperature dependent. Addition to the strained bridge bond of (1) gives the Diels -Alder adduct (13) in tetrahydrofuran at 20°C, but in chloroform at the same temperature the ring-expanded 5,10-epoxydibenzocycloheptene (12) is also formed. Compound (12) becomes the sole product from reaction at 30°C or higher. Cyclopropa [b]naphthalene (2) is inert to dpibf under similar conditions but provides the dimer 6,13-dihydropentacene (15). The triazoloindazole (19) results from reaction of (2) with 4-phenyl-3H-1,2,4-triazole-3,5(4H)- dione.

The product distribution obtained from dehydrochlorination of the benzobicycloheptene 1 is dependent on the reaction conditions. In tetrahydrofuran at high base concentration cyclopropa[b]naphthalene (2) predominates, whereas at low base concentration 6 - chlorobenzo[a]cyclohepta - 1,3,5 - triene (4) is the major product. In dimethyl sulphoxide 2 and 4 are formed in low yields, the ether 10 being the major product.

1,1-Dichloro-2,5-diphenylcyclopropabenzene (1) readily decomposes in solution in halogenomethanes giving the isomeric tropones (4) and (5), and (E)-2,2′3,3′-tetrachloro-4,4′,7,7′-tetraphenyl-1,1′-bicycloheptatrienylidene (8). On mild thermolysis in solution, compound (1) affords a mixture of two dimers, the 1,1′-bicycloheptatrienylidine (8) and an unidentified isomer.

Methyl 10-cyanomethylphenanthrene-9-carboxylate (1e) has been subjected to conditions known to favour Thorpe cyclization, but the desired 5,6- dihydrocyclobuta[l]phenanthrene system (3) was not obtained. An alternative cyclization to give 3-ethoxydibenzo[f,h]isoquinolin-1(2H)- one (4) occurs.

Dehydrohalogenation of (1α,1aβ,9aβ)-1-chloro-1a,9b-dihydrocyclopropa [l]phenanthrene (4b) yields products by way of the corresponding dibenzobicyclohepta-2,4,6-triene (5b) whilst under solvolytic conditions the 7-t-butoxydibenzocyclohepta-1,3,5-triene (llb) is formed by cyclopropyl-allyl ring expansion. When subjected to bromination the cyclopropaphenanthrenes (4a,c) yield halophen-anthrenes(14a) and (15c) by cleavage of an external bond of the cyclopropane ring.

Cycloaddition between 1,1'-bicyclohexenyl(3) and the perhalocyclopropenes (4) affords the la,1b,2,-3,4,5,6,7,8,9,9a,9b-dodecahydrocyclopropa[/]phenanthrenes (5). Whilst halides (5a,b) are resistant to dehydrohalogenation, the difluoro derivatives (5c,d) yield 1,2,3,4,5,6,7,8-octahydrophenanthrene-9-carbaldehyde (12) with base. Under debromination conditions compound (5d) is converted into 1,2,3,4,5,6,7,8,8a,10a-decahydrophenanthrene-9-carboxylic acid (14) probably by way of the ring strained cyclopropene (9).

Heating of the phenanthraquinone 4-aryl-3-(arylimino)semicarbazones (3a) and (3b) led to the phenanthraquinone 4-arylsemicarbazones (6a) and (6b). A statement in the literature that this reaction gives rise to 1-arylimino-1H-cyclopropa[l]phenanthrenes could not be confirmed. The constitution of (6a) was confirmed by independent synthesis from 4- phenylsemicarbazide and phenanthraquinone.

UV-Bestrahlung des Acetylens (Ia) in Cyclohexan unter Argon liefert in relativ kurzer Zeit (4 Std.) 46% des Cyclopropens (IIa).

Whereas treatment of 7,7-dichlorobicyclo[4.1.0]hept-2-ene (2) with potassium t-butoxide yields cyclopropabenzene (4), analogous dehydrochlorination of the 2,3-benzo-analogue (6) does not afford cyclopropa[a]-naphthalene (9). Instead 1-chloromethylnaphthalene (10), 1-t-butoxymethylnaphthalene (11), and the elimination-addition product 1-chloromethylene-1,2,3,4-tetrahydro-2-t-butoxynaphthalene(12) are produced.

Heating of the phenanthraquinone 4-aryl-3-(arylimino)semicarbazones (3a) and (3b) led to the phenanthraquinone 4-arylsemicarbazones (6a) and (6b). A statement in the literature that this reaction gives rise to 1-arylimino-1H-cyclopropa[l]phenanthrenes could not be confirmed. The constitution of (6a) was confirmed by independent synthesis from 4- phenylsemicarbazide and phenanthraquinone.

The alkylidenecycloproparene (1) reacts with potassium t- butoxide to give the ring-expanded heptafulvene (3). Epoxidation of (1) provides the hydroxy ketone (5) probably via the spiro epoxide (4) but carbene additions fail to give spirocycle (7). Photooxygenation of (1a,b) gives products (5),(12)-(14) and (16) which are explicable in terms of initial formation of dioxetan (10); products (13) and (14) result from 1H-cyclopropa[b] naphthalenone (11). By comparison (1c) provides phenanthraquinone acetal (17) in low yield. With osmium tetroxide and sodium periodate , (1a) gives benzophenone (12a) in competition with hydroxy ketone (5a) and 2,2-diphenylcyclobutanaphthalenone (20). The modes of formation of the various products are discussed.

Dehydrohalogenation of (1α,1aβ,9aβ)-1-chloro-1a,9b-dihydrocyclopropa [l]phenanthrene (4b) yields products by way of the corresponding dibenzobicyclohepta-2,4,6-triene (5b) whilst under solvolytic conditions the 7-t-butoxydibenzocyclohepta-1,3,5-triene (llb) is formed by cyclopropyl-allyl ring expansion. When subjected to bromination the cyclopropaphenanthrenes (4a,c) yield halophen-anthrenes(14a) and (15c) by cleavage of an external bond of the cyclopropane ring.

1,1,1a,7a-Tetrachloro-1a,2,7,7a-tetrahydro-2,7-diphenylcyclopropa[b]naphthalene (5) affords an isolable gem-dihalogenocyclopropa[b]naphthalene (7) on dehydrohalogenation, whereas the tetrabromo-analogue (6) does not. The reaction of the gem-dihalide (7) with a small excess of phenyl- or ethyl-magnesium bromide surprisingly results in halogen exchange and formation of gem-dibromocyclopropa[b]naphthalene (8) in high yield. Only with a large excess of Grignard reagent are the halogeno-substituents of (7) replaced by alkyl and aryl groups. Whereas the gem-diethyl derivative (13) is isolable, the gem-diphenyl compound (12) suffers ready ring cleavage, rearranging to a benzo[b]fluorene (18). With the gem-dichloride (7), methylmagnesium iodide effects the equivalent of monohalogen exchange and Grignard reduction to give a benzo[c]fluorene (20).

Photolysis of the pyrazolopyridazines (3) results in the loss of nitrogen. The resultant diradicals (5) do not close to the cyclopropa [d]pyridazines (4) but undergo 1,4-hydrogen transfer to afford the 8-(2'-propenyl)pyridazines (6) instead. In the presence of trapping agents diradicals (5)give ethers (7) with methanol, epoxycyclohepta [d]pyridazines (8) with furan, and the 1,4- and 1,2-addition products (16) and (17) respectively, with butadiene. The formation of (8) and (16)provides the first examples of 1,4-addition of a 1,3-diradical to a diene.

Methyl 10-cyanomethylphenanthrene-9-carboxylate (1e) has been subjected to conditions known to favour Thorpe cyclization, but the desired 5,6- dihydrocyclobuta[l]phenanthrene system (3) was not obtained. An alternative cyclization to give 3-ethoxydibenzo[f,h]isoquinolin-1(2H)- one (4) occurs.

The replacement of the chloro-substituents of 1,1-dichloro-2,5-diphenylcyclopropabenzene (1) can be effected by various organometallic reagents. The products of reaction with Grignard and organolithium reagents and with lithium aluminium hydride have been characterised. Although the gem-diethyl derivative (8) is the only isolated product in which the ring system is retained, spectroscopic evidence is presented which supports the involvement of 1,1-disubstituted cyclopropabenzenes in all the reactions. With methylmagnesium iodide, the cyclopropabenzene (1) suffers the equivalent of Grignard reduction to afford the unanticipated fluorene (25).

Attempted generation of cyclopropa[a]naphthalene (3b) and cyclopropa[l]phenanthrene (3c) by intramolecular 1,3-elimination from the aryllithium derivatives (2b) and (2c), respectively, fails. Instead products from organolithium disproportionation reactions are observed.