Naphthalene Diels-Alder reaction

The study of the cycloaddition behavior of l,l-dichloro-2-neopentylsilene, C Si =CHCH2Bu (2) [3], reveals the high polarity of the Si=C bond and a strong electrophilicity. The [4+2] cycloaddition reactions with anthracene (3), cyclopentadiene (4) and fulvenes (5) proceed as expected surprising, however, the Diels-Alder reactions with dienes are of lower activity, like naphthalene (6) and furans (7). 

Here again the high reactivity is due to the gain of aromatic stabilization in the adduct. Polycyclic aromatics are moderately reactive as the diene component in Diels-Alder reactions. Anthracene forms adducts with a number of dienophiles. The addition occurs at the centre ring. The naphthalene ring system is much less reactive. 

When the cyclic acetylene 260 is generated from a suitable precursor, it undergoes an isomerization reaction spontaneously generating naphthalene (263) and benzo-fulvene (264) as the finally isolable products. Very likely the process begins with a retro-Diels-Alder reaction to the [3]cumulene 261, which in a cascade reaction via the semicydic allene 262 rearranges to 263 and 264 [111]. 

Intramolecular Diels—Alder reactions without prior 1,4-addition of oxygen (cf. previous section) have similarly been postulated for a number of [2.2]paracyclophane analogs. When [2](2,5)furano[2](l,4)naphthalen-ophane (42) is heated in excess dimethyl acetylenedicarboxylate at 100 °C, a polycyclic compound of structure 134 is formed. The mechanism of formation of 134 is most probably as follows 101> the furan moiety reacts as active diene component in an intermolecular Diels—Alder reaction to give 135. This is followed by further intramolecular 1,4-addition with the unsubstituted naphthalene ring as diene component to give the product 133, which has been isolated. 

The reactivity of the produced complexes was also examined [30a,b]. Since the benzopyranylidene complex 106 has an electron-deficient diene moiety due to the strong electron-withdrawing nature of W(CO)5 group, 106 is expected to undergo inverse electron-demand Diels-Alder reaction with electron-rich alkenes. In fact, naphthalenes 116 variously substituted at the 1-, 2-, and 3-positions were prepared by the reaction of benzopyranylidene complexes 106 and typical electron-rich alkenes such as vinyl ethers, ketene acetals, and enamines through the Diels-Alder adducts 115, which simultaneously eliminated W(CO)6 and an alcohol or an amine at rt (Scheme 5.35). 

Aromatic compounds can participate in both [2+2] and [4+2] photocycloaddition reactions with uracil derivatives to give either benzocyclobutane or ethenoquinazoline (barrelene) derivatives, which can then undergo a number of subsequent photochemical reactions. The products obtained are dependent upon the reaction conditions, and thus the photocycloaddition reaction between naphthalenes 470 and l,3-dimethyl-5-fluorouracil 471 in cyclohexane gave 4a-fluoro-5,10-ethenobenzo[/]quinazolines 472 as products as a result of a [4+2] photocycloaddition (photo-Diels-Alder) reaction <2002TL3113, 2003H(61)377>. 

The isopropylation of anthracene gave similar results to that of naphthalene.84 The selectivities for 2-isopropylanthracene (2-IPA) and 2,6-diisopropylanthra-cene (2,6-DIP A) over HM(25) were as high as 91% and 47%, respectively. On the other hand, the selectivities over HY were as low as 59% and 8% for both products. The Diels-Alder reaction of anthracene with propylene occurred at higher temperatures to yield large amounts of the adducts such as 11 -methyl-9, lO-dihydro-etano-anthracene. However, their formation was prevented by the addition of a small quantity of water. 

Aromatic compounds can also behave as dienes.858 Benzene is very unreactive toward dienophiles very few dienophiles (one of them is benzyne) have been reported to give Diels-Alder adducts with it.859 Naphthalene and phenanthrene are also quite resistant, though naphthalene has given Diels-Alder addition at high pressures.860 However, anthracene and other compounds with at least three linear benzene rings give Diels-Alder reactions readily. The interesting compound triptycene can be prepared by a Diels-Alder reaction between benzyne and anthracene 861... 

By far the most important property of benzo[c] furans is their capacity to act as 471-components in cycloaddition reactions. Whereas the reactions described before 1969 were almost always of the Diels-Alder type, more recent investigations have shown that they can also participate in [7 4 + 714]-and [714 + TCgj-addition (Section IV,C). In this chapter Diels-Alder reactions will be discussed. Benzo[c]furans have been used for two main purposes. First, Diels-Alder adducts with olefinic compounds can conveniently be dehydrated to naphthalene derivatives or higher condensed hydrocarbons not easily accessible by other methods second, benzo[c]furans are excellent... 

In Chapter 13 we encountered the Diels-Alder reaction, which involves addition of a reactive alkene (dienophile) to the 1,4 positions of a conjugated diene. Neither benzene nor naphthalene reacts significantly with dienophiles on simple heating, but anthracene does react. Cycloaddition occurs between the 9,10 positions ... 

Tetradehydrodianthracene undergoes 4 + 2-cycloaddition with electron-deficient dienes such as 1,2,4,5-tetrazines.263 The Diels-Alder reactions of [3.3 ortho-anthracenophanes witli A-(p-nitro, chloro, or methoxy-substituted phenyl)malehnides yield approximately equal quantities of inside and outside adducts.264 The photooxidation of bulky water-soluble 1,4-disubstituted naphthalenes with singlet oxygen yields both the expected 1,4- and the unexpected 5,8-endoperoxides.265... 

Mukaiyama reported that 4—10 mol% of Ph2Sn=S and AgC104 catalyzed the Diels-Alder reaction between but-3-ene-2-one (183) or (E)-1 -phenylbut-2-en-1 -one (182) and unactivated dienes 184-186 to afford the products 187-192 in 57-95% yield (Scheme 2.48).80 The reaction with cyclic dienes 185 and 186 was highly endo-selective (dr 99 1). Naphthalene-1,4-dione also participated in the reaction with similar yields. 

This reaction is conducted on a scale of >200,000 tonnes/annum. More recently, another elegant application of electrochemistry on a multi-thousand-tonne scale has been HydroQuebec s investment in a cerium (IV)-mediated oxidation of naphthalene to naphthaquinone, a process licensed from W.R. Grace.87 HydroQuebec then uses the naphthaquinone in a Diels-Alder reaction with butadiene to produce anthraquinone ... 

Due to their reduced aromatic character, naphthalene derivatives more easily undergo [2 + 2] photocydoaddition to give access to cyclobutane derivatives [49]. In some cases, the formal [4 + 2] addition is competitive. In contrast to the ground-state Diels-Alder reaction, the [4 + 2] products from these photochemical reactions result from a multistep reaction. Upon irradiation, the 1-cyanonaphthalene derivative 45... 

Three types of cycloaddition products are generally obtained (Sch. 1). While [2+2] (ortho) and [2+3] (meta) cycloaddition are frequently described, the [2+4] (para or photo-Diels-Alder reaction) pathway is rarely observed in benzene ring systems. With naphthalene systems however, the para cycloaddition occurs more frequently [6,8]. The photo-Diels-Alder reaction and other photocyclization reactions are also observed with anthracene derivatives and higher condensed aromatic compounds. However, these reaction are not treated in this chapter since they are caused by the particular photophysical and photochemical properties of these compounds [6,9]. 

Methyl 3-bromopropiolate has been used in Diels-Alder reactions either as a methoxycarbonyl ketene equivalent3 or for the synthesis of functionalized naphthalenes.10... 

Although several bifunctional chiral Lewis acids have been described in the literature and binding studies have been performed as outlined in Section 7.2, relatively little is known about their use as Lewis acid catalysts. Most notably, l,8-bis(dichloroboryl)naphthalene was treated with various chiral organic amines, alcohols, and acids. The resulting products were found to be efficient catalysts for asymmetric Diels-Alder reactions. The simultaneous coordination of the substrate by both Lewis acid centers is believed to play a significant role (see also Scheme 25). 

Naphthalene oxides. The Diels-Alder reaction of 1,4-diacetoxybutadiene (1) with benzyne (generated from o-benzenediazonium carboxylate, 1, 46) gives the diacetate of l,4-dihydronaphthalene-cis-l,4-diol (2) in 53% yield. The product is converted into 3 by reaction with hydrogen peroxide and catalytic amounts of osmium tetroxide. The monotosylate of 3 is converted into 4 by treatment with base. This epoxy diol has the stereochemistry found in the carcinogenic epoxy diols formed as metabolites of aromatic hydrocarbons. The dimesylate of 3 is converted into the syft-diepoxide 5. 

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