Cycloaddition arenes

Stoddart and cowotkers have extensively exploited the principle of repetitive arene and bis-arene cycloaddition to furans for the design and synthesis of novel macropolycyclic stractures [22,23]. For example, bis-dienophile 21 obtained from ortho-xylene 20 with butyllithium followed by trapping of the resulting bis-arene equivalent 22 with 2 equiv of furan represents a suitable building block for the construction of the macropolycylic belt-like molecule 23. Diels-Alder reaction of 21 with an appropriate bis-diene under alternate thermal and high-pressure conditions afforded macrocycle 23 in good yield, together with an acyclic isomer (Scheme 13.8) [22,23]. 

Wender, P. A., Ternansky, R., de Long, M., Singh, S., Olivero, A., and Rice, K., Arene-cycloadditions and organic synthesis. Pure Appl. Chem., 62, 1597,1990. 

A subsidiary approach involves nuclear modification of the arylsilanes so obtained. The requisite organometallics can be prepared from aryl halides, or by deprotonation of a suitably activated (c.g. methoxy-substituted) arene. A more specialized route involves cycloaddition between alkynylsilanes and diynes. 

Abstract The photoinduced reactions of metal carbene complexes, particularly Group 6 Fischer carbenes, are comprehensively presented in this chapter with a complete listing of published examples. A majority of these processes involve CO insertion to produce species that have ketene-like reactivity. Cyclo addition reactions presented include reaction with imines to form /1-lactams, with alkenes to form cyclobutanones, with aldehydes to form /1-lactones, and with azoarenes to form diazetidinones. Photoinduced benzannulation processes are included. Reactions involving nucleophilic attack to form esters, amino acids, peptides, allenes, acylated arenes, and aza-Cope rearrangement products are detailed. A number of photoinduced reactions of carbenes do not involve CO insertion. These include reactions with sulfur ylides and sulfilimines, cyclopropanation, 1,3-dipolar cycloadditions, and acyl migrations. 

Uemura M (2004) (Arene)Cr(Co)3 Complexes Cyclization,Cycloaddition and Cross Coupling Reactions. 7 129-156 Ujaque G, see Drudis-Sole G (2005) 12 79-107... 

Another recent development in the field of palladium-catalyzed reactions with alkynes is a novel multicomponent approach devised by the Lee group. Starting from a-bromovinyl arenes and propargyl bromides, the assembly ofeight-membered car-bocycles can be realized via a cross-coupling/[4+4] cycloaddition reaction. The authors also presented the combination of a cross-coupling and homo [4+2], hetero [4+2], hetero [4+4] or [4+4+1] annulation leading to various cyclic products [147]. 

Co-catalyzed transformations are concerned mainly with the [2+2+2] cycloadditions of three alkyne groups to give arenes. Another important reaction is the [2+2+1] cycloaddition of alkynes, alkenes and CO to give cyclopentenones, which is the well-known as Pauson-Khand reaction [272]. 

A rather unusual combination of a Ni-catalyzed [2+2+2] cycloaddition of oxaben-zonorbornadiene 6/4-72 with an alkyne 6/4-73 followed by a retro-electrocyclization to give an arene 6/4-75 and benzoisofuran 6/4-76 was described by Cheng and coworkers [298], Under the reaction conditions, 6/4-76 reacted with another molecule of 6/4-72 to give 6/4-77 and 6/4-78 (Scheme 6/4.18). The best yields were obtained employing phenylacetylene with 98% overall yield (58% of 6/4-78 and 40% of 6/4-77). At a lower temperature (18 °C), intermediates of type 6/4-74 could be isolated. On occasion, azabenzonorbornadienes may also be used instead of 6/4-72. 

Although Wender s synthesis was completed prior to Hudlicky s, it was published later [65]. It utilized the technique of mefa-photocycloaddition of arenes that Wender developed into a general method of synthesis for both angular and linear triquinanes. The overall strategy was centered around an intramolecular Diels-Alder cycloaddition for construction of the internal six-membered ring of the target. 

A. Dondoni and A. Marra, Addressing the scope of the azide-nitrile cycloaddition in glycoconjugate chemistry. The assembly of C-glycoclusters on a calix[4] arene scaffold through tetrazole spacers, Tetrahedron, 63 (2007) 6339-6345. 

Organometals and metal hydrides as electron donors in addition reactions 245 Oxidative cleavage of carbon-carbon and carbon-hydrogen bonds 253 Electron-transfer activation in cycloaddition reactions 264 Osmylation of arene donors 270... 

Macrocycles containing isoxazoline or isoxazole ring systems, potential receptors in host—guest chemistry, have been prepared by multiple (double, triple or quadruple) 1,3-dipolar cycloadditions of nitrile oxides, (prepared in situ from hydroxamoyl chlorides) to bifunctional calixarenes, ethylene glycols, or silanes containing unsaturated ester or alkene moieties (453). This one-pot synthetic method has been readily extended to the preparation of different types of macrocycles such as cyclophanes, bis-calix[4]arenes and sila-macrocycles. The ring size of macrocycles can be controlled by appropriate choices of the nitrile oxide precursors and the bifunctional dipolarophiles. Multiple cycloadditive macrocy-clization is a potentially useful method for the synthesis of macrocycles. 

The methodology is useful for a variety of synthetic purposes. The cycloadditions are not subject to steric hindrance. Thus diyne cycloadditions to 2,5-disubstituted furans or pyrroles, followed by elimination of the oxygen or nitrogen bridges, provides an excellent, short route to peri-substituted arenes, as in the following examples 4 6 8... 

Electron-poor olefins with higher oxidation potentials may decrease the rate of electron transfer and other processes competing for deactivation of the iminium salt excited states may increase. Alternate reaction pathways involving olefin-arene 2 + 2 cycloaddition may take place in the photochemistry of 133 with electron-poor olefins (equation 62)120,121. 

The intramolecular [5 + 2] cycloaddition mode has been studied extensively. The chemistry bears a remarkable similarity to the arene-olefin meta-photocycloaddition [53] reaction (e.g. 114... 

In our initial studies on the [5+2] cycloaddition, several metal catalysts were screened. Rhodium(I) systems were found to provide the optimum yields and generality [26]. Since the introduction of this new reaction in 1995, our group and others have reported other catalyst systems that can effect the cycloaddition of tethered VCPs and systems. These new catalysts thus far include chlororhodium dicarbonyl dimer ( [RhCl(CO)2]2 ) [27], bidentate phosphine chlororhodium dimers such as [RhCl(dppb)]2 [28] and [RhCl(dppe)]2 [29], and arene-rhodium complexes [(arene)Rh(cod)] SbFs [30]. [Cp Ru(NCCH3)3] PFg has also been demonstrated to be effective in the case of tethered alkyne-VCPs [31], but has not yet been extended to intermolecular systems or other 2n -components. 

Making elegant use of the intramolecular arene-olefin meta-cycloaddition reaction, Wender and Howbert have achieved a total synthesis of ( + )-cedrene (575) Irradiation of 569 led to an approximately equal mixture of 570 and 571 which... 

A large number of electron-rich polycyclic aromatic systems including anthracenes, azaanthracenes and larger homologues arenes undergo [4 - - 2]-cycloaddition with singlet... 

Planar chiral arene Cr(CO)3 complexes have been shown to undergo highly diastereoselective cycloadditions and Kiindig has extended this protocol to the [3+2] cycloadditions of azomethine ylides (96). Enantiopure ortho- substituted p -benzaldehyde complex 337 underwent condensation with an ot-amino ester to afford imine 338 in the presence of EtaN. Subsequent treatment with methyl acrylate at ambient temperamre in the presence of LiBr and EtaN delivered cycloadduct 339, with excellent stereoinduction and high material yield. Photoinduced oxidative decomplexation in air furnished the final arylpyrrolidines (Scheme 3.114). 

Mukai et al. (36,37) applied the chiral tricarbonyl(r -arene)chromium(0)-derived nitrone 24b in 1,3-dipolar cycloadditions with various alkenes, such as styrene 25 (Scheme 12.11). The analogous nonmetallic nitrone 24a was used in a reference reaction with 25, giving the isoxazohdine 26a with an endo/exo ratio of 82 18. By the apphcation of nitrone 24b in the 1,3-dipolar cycloaddition with 25, the endo/exo-selectivity changed significantly to give exo-26b as the only observable product. The tricarbonylchromium moiety effectively shielded one face of the nitrone, leading to high diastereofacial selectivity. The product exo- 26b was obtained with 96-98% de. 

Die Cycloaddition von ( )-2-Nitro-l-phenylsulfinyl-ethen und 1-Acetoxy-l,3-dienen lie-fert Nitro-arene in 42-65%iger Ausbeute1. 

---