Cyclopropa phenanthrenes, synthesis

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. ... 

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). 

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-... 

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. ... 

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. ... 

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