Methano annulenes synthesis

Heteroannulenes electrophilic reactions, 7, 726 tr-excessive synthesis, 7, 727 nucleophilic reactions, 7, 727 Hetero[l IJannulenes structure, 7, 715 Hetero[ 12]annulenes pyridine-like methano-bridged, 7, 715 Hetero[ 13]annulenes unrestricted structure, 7, 716... 

The preparation of l,6-oxido[10]annulene, described simultaneously by Sondheimer and Shani4 0 and by Vogel, Biskup, Pretzer, and Boll, is illustrative of the rather general synthesis of aromatic 1,6-bridged [10]annulenes starting from 1,4,5,8-tetrahydronaphthalene. Apart from the present compound, the following bridged [10]annulenes have thus far been obtained by this approach l,6-methano[10J-annulene,2-8-9 the ll,ll-dihalo-l,6-methano[10]annulenes,9 10 and 1,6-imino [ 1 OJannulene.11... 

The synthesis of l,6-methano[10]annulene outlined above is an improved version of the method first suggested by Vogel and Roth.13... 

A total synthesis of ( )-dihydrospiniferin-l (149), an unstable furanosesquiterpene from the Mediterranean sponge Pleraplysilla spinifera, has been reported. It is of interest because (149) is the first reported natural product incorporating the novel l,6-methano[10]annulene carbon framework (80JA4274). The key step in the synthesis is the condensation of the aldehyde (150) with methoxymethylenetriphenylphosphorane in toluene to give the bis-enol ether (151). Treatment of (151) with aqueous hydrochloric acid in diethyl ether affords the furan (149). 

While the synthesis of the requisite methano[10]annulenes is not always easy, the [ 2 + 2 + 2] cycloreversion has provided the essential structural variations of cyclopropa fusion into an aromatic moiety that complement other methodologies (Section II.E). Moreover, the sequence lends itself to further exploitation. Thus Vogel s group50 has obtained the dicyanoacetylene adduct 40 which provides phenylacetylene on fvp (equation 9). It is likely that methylenecyclopropabenzene (9) is initially formed as a molecule too... 

In contrast, the synthesis of cycloproparenes monosubstituted at Cl by this route failed. For example, pyrolysis of the adduct derived from ll-niethyl-1,6-methano[10]annulene resulted in formation of styrene, while that from the 11-bromo and 11-cyano derivatives gave only polymeric material. Similarly, only benzaldehyde was isolated upon pyrolysis of the adduct 2 of ll-fluoro-l,6-methano[10]annulenc with acetylenedicarboxylate. Benzaldehyde is the expected hydrolysis product of 1-fluorobenzocyclopropene. 

The synthesis of highly strained linear and angular dicyclopropabenzenes has been attempted without success, since the precursors required for the cleavage could not be synthesized. Thus, iV77-l,6 7,12-diinethano[14]annulene 3 underwent addition to acetylenedicarbonitrile in the wrong sense and did not lead to the required norcaradiene. Cycloaddition of dimethyl acetylenedicarboxlate to cyclopropa-1,6-methano[10]annulene would provide a precursor 4 for the linear dicyclopropabenzene however, the desired cycloadduct was not obtained. In this context, cyclopropa-1,6-methano[10]annulene gave no cycloadduct with 4-phenyl-4//-1,2,4-triazol-3,5-dione. On the other hand, the addition product 5 of 1.6-dimethylenecyclohepta-triene with 1 -bromo-2-chlorocyclopropene reacted with the acetylene derivative, but the twofold dehydrochlorination did not lead to the required norcaradiene. ... 

Sarmah, C.S., and Kataky, J. C.S., A novel synthesis of substituted l,6-methano[10]annulenes using a phase transfer catalyst, Indian J. Chem.. Sect. B, 32, 1149. 1993. 

Synthesis of l,6-methano[10]annulene (5). The first synthesis by Vogel6 involved the route shown, 1) —> (5). Dichlorocarbene (CHC13-KO-/-Bu) reacts... 

The principle developed by Vogel of methano- or oxy-bridging of medium-sized annulenes [8] to strengthen the perimeter has proved advantageous in the synthesis of larger-membered heteroannulenes of various structures. 

An ingenious synthesis of steroidal annulenes has appeared. The close relationship of annulenes to the classical aromatic substance naphthalene stimulated the synthesis of l,6-methano-[10]annuleno-steroids, which are analogues of equilenin (97). The y,5-cyclopropyl-a -unsaturated ketone (98) was the initial target. Treatment of the cyclopropyl ketone (98) with acetic anhydride and methyl orthoformate in the presence of an acid catalyst then gave (99). Conversion of the cycloheptatriene (99) into the requisite 10 c-electron system (100) was then accomplished by dehydrogenation. ... 

The first successful synthesis of benzocyclopropene was reported by Vogel and coworkers and is illustrated below. Though elegant, this method does require the prior, lengthy synthesis of the commercially unavailable l,6-methano[10]annulene. ... 

The first step in this preparation, the epoxidation of 1,4,5,8-tetra-hydronaphthalene, exemplifies the well-known selectivity exerted by peracids in their reaction with alkenes possessing double bonds that differ in the degree of alkyl substitution. As regards the method of aromatization employed in the conversion of ll-oxatricyclo[4.4.1.0 - ]-undeca-3,8-diene to- l,6-oxido[10]annulene, the two-step bromination-dehydrobromination sequence is given preference to the one-step DDQ-dehydrogenation, which was advantageously applied in the synthesis of l,6-methano[10]annulene, - since it affords the product in higher yield and purity. 

One of the spectacular achievements in the syntheses of conjugated it electron systems is that of l,6-methano[10]annulene/ The material is aromatic as evidenced by chemical reactivity and by NMR chemical shifts which are independent of temperature Interestingly, the annulene was prepared by synthesis of its valence... 

Silver nitrate-catalysed rearrangements in methanol of dibromocyclopropyl propellanes have been examined. For example, (80 R = Br) gave a mixture of the corresponding methyl ketal (80 R = OMe) and bicyclo[5,4,0]undec-l(7)-en-2-one, together with minor products. One step in a reported synthesis of 1,7-methano-[12]annulene involved addition of dibromocarbene to tricyclo[4,4,l,0 ]undeca-3,8-diene (81) followed by silver acetate-catalysed ring-opening of the resultant bis-dibromocarbene adduct to give a mixture of isomeric acetates. ... 

A total synthesis of ( )-spiniferin-l involved a rearrangement reaction initiated by polyfluoroalkanosulfonyl fluoride to construct the l,6-methano[10]annulene core of the natural product (Scheme 40). ... 

In the dioxido system, a bridge flipping of the dihydro precursors, 41 42b, was accomplished by heating at 80—100°C for about forty hours. In the present case, synthesis of the < f -l,6-methano-8,13-oxido-[14]annulene has not been possible, because the aw i-dihydro precursor, presumably as the open form 45 a, (c.f. 41), as derived from the anti-tetrabromide, isomerizes spontaneously to the syn compound 45 b at room temperature 159). Consequently, sy -l,6-methano-8,13-oxido-[14]-annulene, 39, is the ultimate product from the anti precursors. 

---