1 //-cyclopropa phenanthrene

Ring contraction of tetrabromobenzocycloheptenedione provided the l//-cyclo-propa[6]naphthalene skeleton 2. Aromatization to the cycloproparene 3 was effected via reduction of the carbonyl groups to alcohols, conversion to p-toluenesulfonates and subsequent reaction with butyllithium. In contrast, the ring contraction of 5,7-dibromodibenzo[n,c]cy-cloheptadien-6-one 4 gave none of the expected 1 //-cyclopropa[/]phenanthren-l -one. The products of the reaction were derivatives of phenanthroic acid, and the cycloproparenone was probably not a reaction intermediate. ... 

The synthesis of li7-cyclopropa[/]phenanthrene (142) presented unexpected difficulties and met many failures. Early approaches used a variety of schemes which were not adequate for this highly reactive compound and invariably produced ring-opened products. Thus irradiation of the substituted indazole 138 resulted in nitrogen extrusion and formation of the biradical 139, which reacted with the solvent, benzene, to form 140. The desired cycloproparene 141 was not formed. Ring contraction of 144, in turn, produced derivatives of 9-phenanthroic acid, the formation of which was shown not to involve phenanthrocyclopropenone (143). °° The attempted 1/3/elimination of 145 was similarly unsuccessful and afforded no 142. ... 

Diphenylisobenzofuran (DPIBF, 44) or furan have been used to intercept cyclopropa[fl]naphthalene (56) and cyclopropa[/]phenanthrene (142). ° ° DPIBF (44) reacts with 1 in THF at 20 °C to form exo and endo adducts 321 and 322 217 unsymmetrical adduct 323, resulting from ring-opening of 1, may also be obtained if the reaction is carried out in CHCl, in particular at higher temperatures." " ... 

The cycloaddition of 1 with 1,2,4-triazines (324), bearing one or more electron-accepting substituents, directly affords the 3,8-methanoaza[10]annulene 325 after loss of N2 from the cycloadduct. Similarly, the tetrazine-dicarboxylate 326 reacts with 1 via cycloaddition/cycloelimination to 327, which has norcaradiene struc-ture. a-Pyrones (328) and 1 undergo cycloaddition/C02 extrusion to 1,6-methano[10]annulenes (329). The sequence cycloaddition/C02 extrusion has also been reported for the reaction of cyclopropa[/]phenanthrene (142) with a-pyrone (328, R = H). ° Substituted 1,6-methano[ 10]annulenes 331 are obtained by analogy via cycloaddition/S02 extmsion of 1 with thiophene-1,1-dioxides (330). ... 

Much more recently, and with the advantage of sophisticated NMR techniques that have become available since the early 1970s, it has been shown that the spiro-3i/-pyrazole structure for 29a is incorrect. It is known that the outcome of diazocyclopentadiene addition to dimethyl acetylenedicarboxylate is dependent upon the five-membered ring substituents In the case at hand, tetraphenyldiazocyclopentadiene adds to the alkyne to give 29a as a labile product that rearranges under the reaction conditions to the 3H-indazole 30a (Scheme 3) 1,3-di-r-butyldiazocyclopentadiene behaves similarly l Thus in the formation of 31a at least, the spiropyrazole 29a is not the substrate and one must question the nature of the educt (29 versus 30) employed in cycloproparene synthesis by the spiro-3i/-pyrazole route. Nonetheless, there can be little doubt that spirocycle 29d is the substrate employed by Mataka and coworkers because, upon thermolysis, the corresponding indazole 30d was isolated. What must be noted here is that the thermal reaction did not provide any of the cyclopropa[/]phenanthrene 31d, but neither did independent photolysis of the isolable indazole 30d in benzene solution a 9,10-disubstituted phenanthrene is formed from diradical interaction with the solvent (equation 7). 

Thus cyclopropabenzene (61a) can be obtained in 45% yield from flash-vacuum pyrolysis of the Diels-Alder adduct 60a formed from l,6-methano[10]annulene (59a) and dimethyl acetylenedicarboxylate. In like manner the benzo analogue 59b provides cyclopropa[a]naphthalene (83%) and the dibenzo derivative 59c gives cyclopropa[/]phenanthrene. Whereas 61a and its linear naphtho[h] analogue are stable entities, 61b suffers explosive decomposition on melting and 61c decomposes at temperatures in excess of — 70° C. 

Direct photolysis of 5f/-dibenzo[a,c]cycloheptene in nonbasic or aprotic solvents such as acetonitrile or cyclohexane gives dibenzonorcaradiene (9, la,9b-dihydro-l//-cyclopropa-[/]phenanthrene), exclusively (0 = 0.087 in acetonitrile), via initial 1,7-hydrogen shift of the... 

Synthesis of selenocyclopropanes has rarely been carried out by routes that result in formation of a bond between selenium and a cyclopropyl carbon atom. The few exceptions that exist involve polycyclic systems containing a cyclopropane moiety. When (l ,la 8,9b)8)-l-chloro-la-trimethylsilyl-1a,9b-dihydrocyclopropa[/lphenanthrene was stirred in a tetrahydrofuran solution of potassium /crr-butoxide and potassium benzeneselenolate a complex reaction mixture was obtained, from which la-phenylseleno-1a,9b-dihydrocyclopropa[/]phenanthrene (1) and (la,laa,9ba)-l-phenylseleno-1a,9b-dihydrocyclopropa[/]phenanthrene (2) were isolated in 10 and 15% yield, respectively, by preparative TLC. Both selenocyclopropanes arise from the same intermediate, la//-cyclopropa[/]phenanthrene, which means that the addition of benzeneselenolate to this alkene is nonregioselective. In contrast, the nucleophilic addition of meth-... 

A similar reaction occurred when (la,laj8,9b 8)-e tfo-l-chloro-la-trimethylsilyl-la,9b-dihydrocyclopropa[/]phenanthrene reacted with a mixture of potassium tcrt-butoxide and potassium benzeneselenolate dissolved in dimethyl sulfoxide. Elimination of chlorotrimethylsilane afforded la//-cyclopropa[/]phenanthrene, which reacted with benzeneselenolate at both ends of the cyclopropene double bond and gave la-phenylseleno-la,9b-dihydrocyclopro-... 

As in the unsubstituted series, preparation of the dihalocyclopropa[u]naphthalenes has proved difficult. Thus, 1,1-difluoro- and l,l-dichloro-l//-cyclopropa[u]naphthalene (20, X = F, Cl) were both prepared from the corresponding 1,4-dibromo compounds 19, but they were stable only in solution at —35 to Likewise, lET-cyclopropa[/]phenanthrene and... 

Similarly, l//-cyclopropa[/]phenanthrene (11) was prepared from the butynedinitrile adduct 10 of the methano derivative of triphenylene. The solid product decomposed slowly, even at — 78°C, but in solution at — 60°C was sufficiently stable for its NMR spectrum to be recorded. 

A similar removal of benzeneselenenic acid from l,l-dichloro-la-phenylseleninyl-la,9b-di-hydro-l//-cyclopropa[/]phenanthrene (2) at ambient temperature was used to generate 1,1-dichloro-l//-cyclopropa[/]phenanthrene as a short-lived intermediate which was trapped by addition of methanol.Elimination of the elements of HSe Mcj from 3, derived from la-methylselenacyclopropa[/]phenanthrene and la,9b-dihydro-l//-cyclopropa[/]phenanthrene after alkylation, gave a mixture of the alternative cyclopropene, which were both trapped with furan. 

Several extensions of this approach have been attempted, but none was successful. Only a faint odor results from the attempted synthesis of cyclopropa[Z)]naphthalene and none of the expected cyclopropa[a]naphthalene or cyclopropa[/]phenanthrene were generated in the corresponding reactions.- The same difficulties have been experienced with other benzyl derivatives. The reaction of 2-bromobenzyl bromide, 2-bromobenzyl chloride and 2-iodobenzyl bromide with butyllithium gave (partially) reduced bibenzyls or 9,10-dihydroanthracene, but no benzocyclopropene. Similarly, lithiation of 2-bromobcnzylsulfonates afforded only trace amounts (< 5%) of bcnzocyclopropene, while only methoxymethylbenzene was isolated on treatment of l-methoxymethyl-2-trimethylsiIylbenzene with fluoride ions. ... 

Base treatment of the precursor of cyclopropa[ )]phenanthrene produced a mixture of 2-and 3-chloromethylphenanthrene (7 a and 7 b). Interception studies showed that the ring-opened products in the anthracene and phenanthrene series are not derived from intermediate cyclopropenes, but result probably from deprotonation of the benzylic position to give a cyclo-propylmethyl anion, which rearranges to a homoallylic anion. The latter may then react further to the chloromethyl derivative. ... 

The application of the Billups approach to l//-cyclopropa[/]phenanthrene requires dehydrochlorination and subsequent double-bond isomerization of l-chloro-la,9b-dihydro-l/7-cyclo-propa[/]phenanthrene (8). The direct double bond migration did not, however, occur in this system, but was achieved indirectly by nucleophilic trapping of the intermediate cyclopropene, la77-cyclopropa[/]phenanthrene (9) with methaneselenolate - or methanethiolate. Base-induced elimination of the dimethylselenonium or dimethylsulfonium derivative 10 did not allow isolation of the expected cycloproparene, but in the presence of furan a mixture of interception products 12-14 derived from l/f-cyclopropa[/]phenanthrene 11 and its la//-isomer 9 was obtained. 

In contrast, reaction of the dichlorocarbene adduct to 9-mcthoxyphenanthrene with potassium tert-butoxide did not lead to the cycloproparene, but proceeded by dehydrochlorination to 1 -chloro-9-methoxy-laf/-cyclopropa[/]phenanthrene (16) as a reactive intermediate. This then rearranged to a vinylcarbene which, in turn, underwent intramolecular C —H bond insertion and aromatization to phenanthro[9,10-h]furan (17). ... 

Methyl substituents at C2 and C5 have an insufficient stabilizing cfl ect and l,l-difluoro-2,5-dimethylbenzocyclopropene was not isolable from the reaction of 1,6-dichloro-7,7-difluoro-2,5-ethylbicyclo[4.1.0]hept-3-ene with potassium /er/-butoxide instead tert-butyl 2,5-dimethylbenz-oate was isolated in 81 % yield.Similarly, the attempted synthesis of 1,1-difluorooctahydro-l//-cyclopropa[/]phenanthrene was unsuccessful, and only a small amount (16%) of octahy-drophenanthrene-9-carbaldehyde was isolated from the adduct of l,2-dichloro-3,3-difluorocy-clopropene and l,l -dicyclohex-l-enyl. ... 

When the indazene route was applied to cyclopropa[/]phenanthrene, the reaction product was not the expected cycloproparene, but a 9,10-disubstituted phcnanthrene, which is derived from reaction of the intermediate diradical with the solvent. ... 

Diphenylisobenzofuran also reacted with cyclopropa[a]naphthalene to give an adduct 9 of unknown stereochemistry in ca. 40% yield however, cycloadducts of cyclopropa[Z ]naph-thalene have not as yet been described. Cyclopropa[/]phenanthrene underwent cycloaddition with furan to give the endo-aAAuci 10 (28%) and its evo-isomer 11 (17%). ... 

Naphtho fusion gives cyclopropa[6]anthracene. 2,3-Naphtho fusion gives cyclopropafajanthracene. Dibenzo fusion gives cyc)opropa[/]phenanthrene. 

A more recent variation of the general procedure described in the previous section involves the use of adducts of l-bromo-2-chlorocyclopropene as substrates for the double elimination reaction.Thus, l/f-cyclopropa[6]phenanthrene (4) was obtained in 89% yield in the final step of a sequence that included cycloaddition to diene 1 followed by aromatization. ... 

The cyclopropane ring in la,9b-dihydro-l//-cyclopropa[l]phenanthrene (13) was opened in two different ways upon reduction with lithium or sodium and gave rise to the formation of dibenzocycloheptadiene (14), 9-methylphenanthrene (15), and 9-methyl-9,10-dihydrophenan-threne (16). The proportion of products formed depended on the number of equivalents of the reducing agent and the duration of the reaction. 

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