Phenanthrenes cycloaddition

Ethyl 1 /T-azepine-l-carboxylate (1) and l,3-diphenyl-2/7-cyclopenta[/]phenanthren-2-one (26) (phencyclone) in refluxing benzene undergo a rapid peri- and regioselective cycloaddition to give the [4 + 2] 7t-e rfn-adduct 28 and not, as was first proposed, a [6 + 2] 7r-adduct.264 Subsequently, however, it was found that at room temperature a [2 + 4] 7r-cw/<>-adduct 27 is formed which readily undergoes a Cope rearrangement to the [4 + 2] endo,anti-adduct 28. 

Phenanthrene-l,4-diones have been prepared [52] by cycloaddition of a-substituted styrenes with an excess of 1,4-benzoquinone (Equation 2.18). Initial cycloadducts are oxidized by 1,4-benzoquinone. 

Dihydrovinylphenanthrenes are more reactive than the corresponding vinyl phenanthrenes and undergo Diels-Alder reactions easily. They have been used in the synthesis of polycyclic aromatic compounds and helicenes. Examples of cycloaddition reactions of the 3,4-dihydro-1-vinylphenanthrene (70), [61] 3,4-dihydro-2-vinylphenanthrene (71) [68] and l,2-dihydro-4-vinylphenanthrene (72) [69] are reported in Equation 2.22 and Schemes 2.27 and 2.28. 

Although 1-vinylnaphthalene thermally reacts with 4-acetoxy-2-cyclopenten-1-one (98) to regioselectively afford 99, the isomer 2-vinylnaphthalene gives the same thermal cycloaddition with low yield (30 %) and reacts satisfactorily only with 98 at 10 kbar (Scheme 5.10). Both products 99 and 101 were converted into the cyclopenta[a]phenanthren-15-one (100) and cyclopenta[c]phenanthren-l-one (102) isomers. Acetoxyketone 98 acts as a synthetic equivalent of cyclo-pentadienone (114 in Scheme 5.14) in cycloaddition reactions [33]. 

The only reported 1,2-addition providing a relatively stable adduct is that of a 1,2-cycloaddition of phthalazinedione to indene (Scheme 40). Compound 162 was isolated and characterized (66JOC3862 71CC695). A similar 1,2-addition reaction to the 9,10-double bond of phenanthrene was also reported but not firmly documented (66JOC3862). 

The partially hydrogenated phenanthrene derivative 18 (entry 4) is a very moderate diene due to the steric crowding caused by the substituents and the anulated rings, and it reacts even with highly reactive dienophiles such as maleic anhydride (MA) or N-phenylmaleic imide only at high pressure. The minor product 20 in the reaction with MA obviously stems from diene 21. This can be explained by a double-bond isomerization 18 - 21 prior to the cycloaddition, certainly catalyzed by traces of acid present in the MA. In the absence of acid only the Diels-Alder adduct 22 derived from diene 18 was observed. In the reaction of diene 23 with MA (entry 5) a similar sequence of steps was observed. A [1,5] shift of the C—O bond in 23, again certainly acid-catalyzed, produces the diene 26 followed by the Diels-Alder reaction with MA to give 24 and 25. 

Two other synthetic routes to derivatives of this ring system should be mentioned here, and the transformations are shown in Scheme 54. The phenanthrene-fused fV-aryldihydro[1.2.4]triazine 274 was found to undergo 1,3-dipolar cycloaddition with diarylnitrilimine to give the cycloadduct 275 <1997J(P1)1047. This transformation is entirely analogous to that taking place with a fused oxadiazine derivative, as discussed in Section 11.19.6.1. 

Other cyclopropaphenanthrenes are, however, isolable. Recently, Billups et al. described the synthesis of dicycIopropa[b,/i]phenanthrene (165) and of its dihydro derivative 166 starting from tetramethylidenecyclohexane 164 by the cycloaddition... 

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). ... 

Bis(phenylazo)phenanthrene 174, for which the cyclic form 175 dominates reactivity at low concentrations, reacts with acrylonitrile in dry toluene at 55 °C for 48h to give the o o-adduct 2,4-diphenyl-3a,6a-(biphenyl-2,2 -yl)-6-exo-cyano-l,3a,4,5,6,6a-hexahydropyrrolo[2,3-r7 -2,3-triazol-2-ium-l-ide 176 (60% ) as the only product of cycloaddition. Reaction with other alkenes, for example, A -phenylmaleimide, leads to a mixture of endo- and o ti-products, cf. 177 and 178 <1996J(P1)1623>. 

Nitrogen heterocycles continue to be valuable reagents and provide new synthetic approaches such as NITRONES FOR INTRAMOLECULAR -1,3 - DIPOLAR CYCLOADDITIONS HEXAHYDRO-1,3,3,6-TETRAMETHYL-2,l-BENZISOX AZOLINE. Substituting on a pyrrolidine can be accomplished by using NUCLEOPHILIC a - sec - AM IN O ALKYL ATION 2-(DI-PHENYLHYDROXYMETHYL)PYRROLIDINE. Arene oxides have considerable importance for cancer studies, and the example ARENE OXIDE SYNTHESIS PHENANTHRENE 9,10-OXIDE has been included. An aromatic reaction illustrates RADICAL ANION ARYLATION DIETHYL PHENYLPHOSPHONATE. 

A synthesis of ( )-tylophorine (213) has been based on the discovery that vanadyl trifluoride (VOF3) can be used to convert 1,2-diarylethylene into phenanthrenes in high yield. In the top sequence shown in Scheme 34, ring closure is accompanied by dehydrogenation (77CC826). In a second synthesis, ( )-tylophorine (213) is the result of an intramolecular version of a Diels-Alder cycloaddition of a conjugated diene with an imino dienophile (Scheme 34, lower sequence) (79JA5073). 

The cycloaddition reactions of singlet phenanthrenes with t-1 and c—1 have been investigated by Caldwell and co-workers (11). The reaction of singlet 9-cyanophenanthrene with t-1 in benzene solution yields adducts 89 and 90 in 65 and 15% yield, respectively, while reaction with c-1 yields the crowded cis, endo isomer 91 and t-1, which reacts to yield 89 and 90. 

The thermal intramolecular 2 + 2-cycloaddition of 4,4,-disubstituted-2,2/-bis(phenyl-ethynyl)biphenyls (1) yielded the intermediate l,2-diphenylcyclobuta[l]phenanthrenes (2), which could be trapped with 2,3,4,5-tetraphenylcyclopenta-2,4-dione (3) to produce the Diels-Alder adduct (4). Thermal decarbonylative ring opening of (4) gave 9,10,11,12,13,14-hexaphenylcycloocta[l]phenanthrenes (5) as the final product in 12-23% yield (Scheme l).1... 

A tandem sequence of double [2,3]-sigmatropic rearrangement-six-electron electro-cyclization-4 + 2-cycloaddition has been shown to convert acyclic ene-bis(propargyl alcohols) such as (71), via the corresponding bis-sulfenic ethers such as (72), into anthracene (with an intermolecular final cycloaddition) or phenanthrene or related (with an intramolecular cycloaddition) skeletons. The sequence is illustrated in Scheme 12 for synthesis of a steroid skeleton, estra-l,3,5(10)-trien-17-one (73).81... 

The Diels-Alder cycloaddition of 1,2-dimcthylcnc 2.n]mclacyclophancs (83) with DMAD followed by aromatization (84) and photoinduced transannular cycliza-tion produced phenanthrene-anellated polycyclic aromatic hydrocarbons (85) (Scheme... 

The constitution of the angular syn-bisdienophile 74 (see Scheme 20) maintains the bicyclic nature of the two dienophilic units. However, the [a,c]-fusion present in the phenanthrene constitution reduces the end-to-end symmetry of the rc-systems, rendering the two olefinic carbon atoms in each dienophilic unit constitutionally-heterotopic. The effect of this reduction in the symmetry of the 7t-systems in 74 upon the diastereoselectivities exhibited in its cycloadditions was of considerable interest to us. Furthermore, the incorporation of two phenanthrene units into a macropolycyclic belt could ultimately lead to the preparation of an angular isomer 70 of [12]cyclacene 50 (Fig. 20). Compared with [12]cyclacene 50, the angular isomer 70 has some appealing electronic features associated with it. 

Eq. (29)], and phenanthrene quinone [Eq. (28b)], leads to the [4 + 2] Diels-Alder adducts the two benzoquinone adducts add a second molecule of the quinone 1 resp. 2, forming the trioxyphosphoranes. The mechanism of this [4 + 2] cycloaddition, either symmetry allowed or stepwise, is not yet clear (73). 

Phenanthrene undergoes a cycloaddition reaction (23) with dimethyl fumarate to give a cyclobutane [50] and an oxetane (Creed and Caldwell,... 

As has been mentioned earlier, it is often very difficult to distinguish between and identify the roles of exciplexes (and excimers) and biradicals in cycloaddition reactions. Caldwell and Creed (1978b) have studied the cycloaddition of dimethyl fumarate to phenanthrene and found that the quantum yield of the cyclobutane photoaddition product is increased in the presence of oxygen. It was suggested that oxygen enhances intersystem crossing in the triplet biradical formed between the two reactants. Nitroxide radicals have also been found to increase intersystem crossing (Sj -> Tj) in carbocyanines when nonpolar solvents are used (Kuzmin et al., 1978). When polar solvents are employed full electron transfer takes place. 

Scheme 9.1. [2 -r 2] cycloaddition with formation of acenaphthylene 101 and phenanthrene 102... 

Starting material. " At higher temperatures one obtains products derived from a cycloaddition-cycloreversion sequence, such as phenanthrene (from 71 and 72) and acenaphthalene (from 72). 

A route to partially hydrogenated phenanthrenes relies on the Diels-Alder reaction of a benzyne to an annulated furan, e.g. (501) - (503) (Scheme 117). However, regiochemistry raises its ugly head when both the furan and the benzyne are nonsymmetrically substituted (Scheme 118). Hence, the [4 + 2] cycloaddition of 3-methylbenzyne with 2>substituted furans (504) gave the anti and syn adducts (506)... 

Kojima and co-workers also examined the photo-oxidation of stilbenes in zeolite Y [150]. The presence of O2 in the stilbene-NaY sample led to a red-shifting of the tail end of the diffuse reflectance spectrum and was assigned to the charge-transfer complex with O2. Upon excitation at 313/366 nm, both cis- and /ra .v-stilbene undergo photo-oxygenation to form benzaldehyde. Phenanthrene, the expected product from the ]2 -f 4] cycloaddition reaction of excited m-stilbene, was also formed. The details of the mechanism leading to benzaldehyde and phenanthrene... 

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