Cyclopropa naphthalenes

The anion derived from l,l-bistrimethylsilyl-l//-cyclopropa[ ]naphthalene reacts with thioxanthone to yield the red l-thioxanthenylidene-l//-cyclopropa[ ]naphthalene 368 (Scheme 89) <1998JOC1583>. 

In this way cyclopropa[/ ]naphthalene and -anthracene and their derivatives are available. The substrates 52 required for these latter cycloproparene syntheses are obtained... 

Reductive 1,2-eIimination of chlorine and bromine from adducts of l-bromo-2-chlorocyclo-propene (see Section 5.2.2.1.2.5.) with oxygen and sulfur hetarenes has served in the synthesis of a number of cycloproparenes. This transformation is effected by low-valent titanium together with lithium aluminum hydride or an organolithium compound. Thus, reaction of the adduct 3 of l-bromo-2-chlorocyclopropene and 1,3-diphenylisobenzofuran with tita-nium(III) chloride and lithium aluminum hydride overnight in tetrahydrofuran led to elimination of both halogens together with extrusion of the oxygen and formation of 2,7-diphenyl-l/f-cyclopropa[ ]naphthalene (4) in 72% yield. 

Silylation of cyclopropa[ ]naphthalene proceeded indirectly to the disubstituted product 1,1-bis(trimethylsilyl)-l//-cyclopropa[Z ]naphthalene in 60% yield,and a sequential double deprotonation/silylation procedure was used to synthesize l,l-bis(trimethylsilyl)-1//-cyclo-propa[A]anthracene in 92% yield.Silylation of dicyclopropa[A,g]naphthalene has so far been unsuccessful. ... 

Two unsuccessful approaches to alkylidene-l//-cyclopropa[/)]naphthalene are known. 2,7-Bis-(trimethylammonio)-l-trimethylammoniomethyl-la,2,7,7a-tetrahydrocyclopropa[/)]naphthal-ene was synthesized as a precursor to 1-methylene-l 7/-cyclopropa[Zt]naphthalene, but the result of the elimination was not reported.A potential precursor of l-isopropylidene-li/-cyclo-propa[fc]naphthalenc was synthesized via addition of isopropylidenecarbene to 1,4,5,8-tetrahyd-ronaphthalene, but all attempts to aromatize the adduct were unsuccessful. ... 

Heating cyclopropa[ ]naphthalene in refluxing anhydrous benzene with He labeled Cgg resulted in the formation of a fullerene adduct 7 of the diradical. The adduct was characterized by He NMR.s°... 

Similarly, alkane- and arenesulfonyl isocyanates gave 2-sulfonyl-2,3-dihydroisoindol-l-ones 11 with benzocyclopropene. 2,3-Dihydroisoindol-l-one was produced as a byproduct in 4% yield in the case of arenesulfonyl isocyanates. Cyclopropa[ ]naphthalene underwent addition to 4-phenyl-47/-l,2,4-triazole-3,5-dione at 20°C almost instantaneously to give an indazole 12 in 92% yield.Both reactions are believed to occur by electrophilic attack on the cyclo-proparene and may involve a zwittcrionic intermediate. When benzyne was generated from benzenediazonium-2-carboxylate in refluxing dioxane in the presence of cyclopropa[Z ]naph-thalenc, 5//-naphtho[2,5-a]indene was formed in 13% yield. 

Cycloaddition of 2//-pyran-2-one with cyclopropa[/>]naphthalene occurred, again, at the exocyclic double bond and gave dihydroindenones 22 after ring-expansion. 

Cyclopropa[ )]naphthalene reacted with acetylenebis(phenyliodonium) triflate via a formal [2 -I- 2] cycloaddition again at the exocyclic double bond. Hydrolysis of the supposed cycloadduct occurred via ring expansion and elimination of the mono-iodonium acetylide to a iodonium salt 23. 

Attempted formation of t/ -tricarbonylchromium(0) complexes of cyclopropa[/)]naphthalene (3) or l/f-cyclopropa[6]anthracene (7) by reaction of these ligands with tris(acetonitrilc)tricar-bonylchromium(O) resulted in the formation of the corresponding annulated cyclobutenone derivatives 6 and 8 in 57 and 54% yield, respectively, as the result of carbonyl-insertion reactions. 

Aromatization of dihalocarbene adducts to 1,4-cyclohexadiene or synthetic equivalents is the method of choice for the synthesis of the parent benzocyclo-propene (1). ° The mechanism of the aromatization step of the intermediate 7,7-dihalogenobicyclo[4.1.0]hept-2-ene (51) has been shown by labeling experiments with 51 depleted of C at Cl, to proceed via a series of elimination and double bond migration steps via cyclopropene- and alkylidenecyclopropane intermediates 52 to 54 with preservation of the original carbon skeleton. The synthesis of the benzannelated homologue, l//-cyclopropa[b]naphthalene (42), by the same route confirms these findings. Some skeletal rearrangement has, however, been observed in an isolated case. ... 

Alder-Rickert cleavage has not been widely used for cycloproparene synthesis, since the preparation of the precursors is often tedious, except for the simple cases like 7,7-difluorobenzocyclopropene (21). The approach offers, however, decisive advantages in special situations. If the Alder-Rickert cleavage is carried out under flash-vacuum pyrolysis conditions, the products may be isolated under neutral conditions and at low temperature. Thus the synthesis of the highly reactive li/-cyclopropa[a]naphthalene (56) by pyrolysis of 68 has been achieved by this approach. Several other approaches to 56 failed. 

In the series of o-fused cyclopropanaphthalenes there is a marked difference between the linear compound 42 (l//-cyclopropa[I>]naphthalene) and the angular... 

The linear cyclobuta[e]cyclopropa[b]naphthalene (114) was synthesized very early by the carbene addition approach, while the synthesis of the angular isomer failed. The most strained of all isolable cycloproparenes, 1,4-dihydrocyclo-propa[b,g]naphthalene (115), was obtained originally by the same approach from the tetrabromide 116. The synthesis was recently improved. An alternative access to 115 via 117 as precursors is also available. The strain energy of 116 is extremely high, and it explodes upon melting (132 °C). ... 

In contrast, isomers of 115 have so far not been isolated. An early attempt to generate cyclopropa[a,e]naphthalene (118) failed. More recently, the generation of dicyclopropa[a,c]naphthalene (119) was attempted by reaction of 120 with base. When the aromatization was carried out in the presence of DPIBF (44), stereoi-someric bis-adducts of cyclopropenes were isolated. However, the adducts provide no evidence for the formation of 119 as a reactive intermediate, since they are formed by sequential elimination-cycloaddition via 121. Cyclopropene interception of 121 is faster than further elimination to 119. The failure of the reaction to produce 119 has been attributed to the high strain energy of the product, which is estimated some 2 8 kcal/mol higher than that expected for two isolated cyclopropene units. ... 

The structures of several substituted cycloproparenes, i.e., l,l-dichloro-2,5-diphenylbenzocyclopropene (22), l,l-dimethoxycarbonyl-2,5-diphenylbenzo-cyclopropene (264), 2,5-diphenylbenzocyclopropene (265), and l//-cyclopropa[fc]naphthalene (42), have also been determined, and are consistent with those of the unsubstituted compounds. Even the most strained member of the family, dicyclopropanaphthalene (115), exhibits no further deformations than the parent 1. The cycloproparene structure is also preserved in alkylidenecyclo-proparenes with only minute changes. The exocyclic double-bond length of alky-lidenecycloproparenes lies in the range of 1.343 to 1.346 A. ... 

The strain of 1 has been determined experimentally from silver-ion catalyzed methanolysis to be ca. 68 kcal/mol, and that of cyclopropa[/j]naphthalene to be 65-67 kcal/mol. Combustion calorimetry gave a value of 67.8 kcal/mol. For dicyclopropa[/>,g]naphthalene (115) a lower limit of 166 kcal/mol was found. These energies are well reproduced by ab initio, and even by semiempirical calculations. Thus 3-2IG calculates a strain energy of 70 kcal/mol while 3-2IG gives 71.6. At the MP2/6-31G level the strain of 1 is 71.3 kcal/mol, while that of cyclopropene amounts to 57.4 kcal/mol. This latter value compares well with the experimental one, which is 52.6 kcal/mol. While semiempirical calculations have been found unreliable for cycloproparene structures, the calculated strain energies are usually close to reality for MINDO/3, MNDO, and force-field-SCF calculations. The strain energies of the dicyclopropabenzenes (100, 102) have been predicted to be 133 and 140 kcal/mol, respectively, and that of tricyclo-propabenzene (260) to be 217 kcal/mol (3-21G). ... 

Numbering of cyclopropa[6]naphthalenes. Numbers in parentheses specify positions. 

When dissolved in cold fluorosulfonic acid, 1,1 -dihalogenobenzocyclopropenes ionize to benzocyclopropenyl cations (e.g., 282-286) which are stable under NMR conditions. " The same holds for l,l-dihalogenocyclopropa[( ]naphthalenes which ionize to 287-288, while the cation derived from the cyclopropa[a] isomers (289) is very short lived. No ions may be observed upon dissolving 1,1-dihalo-genocyclopiopa[fc]anthracenes (130,131) in fluorosulfonic acid. The NMR data of some fluorobenzocyclopropenyl cations are summarized in Table 4. 

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." " ... 

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