Cycloadditions of benzene derivatives

The [2 + 2] cycloaddition of benzene derivatives with alkenes was also carried out using photosensitization. Maleimide 36 was added to benzene in high yields (Scheme 5.8, reaction 16) [42]. In this case, the sensitizer acetophenone 37 transfers its triplet energy to 36, after which the cycloadduct VII reacts immediately with an... 

De Keukeleire, D., Bako, P., and Van der Eycken, E. (2000) Intramolecular ortho and meta photocycloadditions of 4-phenoxybut-l-enes substituted in the arene residue with carbomethoxy, carbomethoxymethyl, and 2-carbo-methoxyethyl groups. Journal of Photochemistry and Photobiology A Chemistry, 133, 135-146 (c) Wender, P.A. and Dore, T.M. (1995) Intra and inter-molecular cycloadditions of benzene derivatives, in CRC Handbook of Organic Photochemistry and Photobiology (eds W.M. Horspool and P-.S. Song), CRC Press, Boca Raton, pp. 280-290. 

Gilbert, A. (2004) Intra- and intermolecular cycloadditions of benzene derivatives, in CRC Handbook of Organic Photochemistry and Photobiology,... 

The same authors showed that in the cycloaddition of northebaine derivatives the reaction time with microwave heating was considerably shorter than when conventional heating was used [54], When, however, cycloadditions were performed in benzene, a poor absorber of microwave irradiation, microwave heating did not result in a significant increase in the rate of the reaction. 

Sometimes the formation of benzene derivatives can be explained by cycloaddition rather than by ketolization. Thus the excellent preparation of substituted benzophenones 553 from 2//-pyrans 552 on heating with acetic anhydride253 is interpreted as in Scheme 30. 

Ortho photocycloadditions of benzene derivatives to maleic anhydride have been tabulated in Table 1. Only the structures of the primary ortho adducts are given, but these are not the isolated adducts They always undergo endo [2 + 4] cycloaddition with maleic anhydride, yielding 1 2 adducts. An interesting feature to be seen from Table 1 is that substituents on the benzene (alkyl, phenyl, or halogen) always turn up at the position most remote from the site of addition. In view of the different nature of these substituents, it seems that steric rather than electronic factors are responsible for this regioselectivity. 

Benzene and cyclooctatetraene (COT) derivatives are formed by [2+2+2] and [2+2+2+2] cycloadditions of alkynes. At first the metallacyclopropene 107 and metallacyclopentadiene 108 are formed. Benzene and COT (106) are formed by reductive elimination of the metallacycloheptatriene 109 and the metallacyclononate-traene 110. Formation of benzene by the [2+2+2] cycloaddition of acetylene is catalysed by several transition metals. Synthesis of benzene derivatives from... 

Some efforts have also been done to induce chirality in the intramolecular [2 + 2] photocycloaddition of benzene derivatives using a chiral auxiliary [88]. 141b was isolated with a diastereoselectivity of 17% from the intramolecular photocycloaddition of the salicylic acid derivative 140b (Scheme 35) [89]. After an initial [2 + 2] cycloaddition, reversible thermal and photochemical rearrangements took place. These equilibria can be displaced by an acid catalyzed and irreversible addition of methanol to the intermediate P. 

Cycloaddition of thiophene 1,1-dioxides with alkynic dienophiles leads to the formation of benzene derivatives with elimination of sulfur dioxide. Thus, the unstable parent thiophene 1,1-dioxide 1 reacts with diethyl acetylenedicar-boxylate and cyclooctyne to give diethyl phthalate and benzocyclooctene, although in low yields (Scheme 53) [132, 175]. Cycloadditions with alkenic and alkynic dienophiles had been used as evidence for the generation of 1 until spectroscopic evidence became available [46]. Tetrachlorothiophene dioxide 53 reacts with phenylacetylene [35] and a cyclic alkyne 92 [176] to give 1,2,3,4-tetrachloro-5-phenylbenzene and compound 93, respectively (Scheme 54). 

A comprehensive review (260 refs.) on the synthesis of carbohydrates from noncarbohydrate sources covers the use of benzene-derived diols and products of Sharpless asymmetric oxidation as starting materials, Dodoni s thiazole and Vogel s naked sugar approaches, as well as the application of enzyme-catalysed aldol condensations. The preparation of monosaccharides by enzyme-catalysed aldol condensations is also discussed in a review on recent advances in the chemoenzymic synthesis of carbohydrates and carbohydrate mimetics, in parts of reviews on the formation of carbon-carbon bonds by enzymic asymmetric synthesis and on carbohydrate-mediated biochemical recognition processes as potential targets for drug development, as well as in connection with the introduction of three Aldol Reaction Kits that provide dihydroxyacetone phosphate-dependent aldolases (27 refs.). A further review deals with the synthesis of carbohydrates by application of the nitrile oxide 1,3-dipolar cycloaddition (13 refs.). ... 

Cycloaddition of alkynes is an easy and efficient approach towards the synthesis of benzene derivatives [21]. However, fluorine-containing alkynes are rarely shown to undergo such reaction [22]. [RUj(CO)32], with phosphine or some phosphine derivative as additive, is able to cyclotrimer-ize the trifluoromethyl group substituted internal alkynes [23]. Particularly, when 2-(diphenylphosphino)benzonitrile (2-DPPBN) is used, the cyclotrimerized unsymmetrical benzene derivative forms in 77-92% yield with more than 98% regioselectivity depending upon the substituent in Ar... 

Cycloaddition. In recent years, [2+2+2] cycloadditions are no longer limited to the synthesis of benzene derivatives. Many cycloadditions of various carbon and heteroatoms component combinations have achieved great success. In 2005, Evans and co-workers developed an asymmetric [2-I-2-I-2] cycloaddition of enynes 9 with symmetrical and unsymmetrical alkynes 10 to give 5-6 fused products 11 and 12 in good yields and excellent ees (Scheme 5) (14). Under the optimized conditions, highly regio- and enantioselective products were obtained from the reaction of enynes with unsymmetrical alkynes. 

Diels-Alder cycloaddition of thiophene 1,1-dioxides with alkynic dienophiles leads to the formation of benzene derivatives directly via elimination of a sulfur dioxide. 

Construction of benzene derivatives bearing bulky substituents can be easily achieved by [4-1-2] cycloadditions of highly congested thiophene 1,1-dioxides with alkynic dienophiles (Scheme 107) [59, 109]. 

Takahashi T, Xi Z, YamazaM A et al (1998) Cycloaddition reaction of zirconacyclopentadienes to alkynes highly selective formation of benzene derivatives from three different alkynes. J Am Chem Soc 120 1672-1680... 

There are large number of cycloaddition reactions of benzene and its derivatives. Correlation diagram can be constructed to predict them which can be represented by examples of ortho-, meta- and para-cycloadditions of benzene and ethylene or benzene and butadiene. Ortho-, meta- and para-additions give different products. 

In this chapter we outline advances in the ruthenium-mediated alkyne [2 + 2 + 2] cycloaddition reactions. These can be classified into two major categories in terms of the types of products (1) syntheses of benzene derivatives via alkyne [2 + 2 + 2] cycloadditions and (2) syntheses of heteroaromatics via [2 + 2 + 2] cocycloadditions of alkynes with nitriles or heterocumulenes. Benzene ring-forming reactions are essentially prototypes of the corresponding heteroaromatic annulations. Therefore, the first class of reactions is reviewed in the next section and followed by a discussion of the second class of reactions. The mechanistic aspects and synthetic applications of ruthenium-catalyzed [2 + 2 + 2] cycloadditions are also described to exemplify the scientific and practical significance of ruthenium catalysis. 

Since the first reaction was discovered by Reppe and Schweckendiek [4], numerous transition metals have been used to promote alkyne [2 + 2 + 2] cycloadditions [1]. The majority of attention has focused on group 9 and 10 transition elements, including Co, Rh, Ni, and Pd. In comparison to these precedents, [2 + 2 + 2] alkyne cycloaddition reactions involving group 8 metals have been relatively neglected. However, over the past decade, there has been significant progress in efficient and selective [2 + 2 + 2] alkyne cycloadditions catalyzed by ruthenium. In this section we review the synthesis of benzene derivatives via alkyne [2 + 2 + 2] cycloaddition both stoichiometrically and catalytically. 

The benzene derivative 401 by the intermolecular insertion of acrylate[278], A formal [2 + 2+2] cycloaddition takes place by the reaction of 2-iodonitroben-zene with the 1,6-enyne 402. The neopentylpalladium intermediate 403 undergoes 6-endo-lrig cyclization on to the aromatic ring to give 404[279],... 

Intramolecular dipolar azide-olefin cycloaddition of 723 took place upon heating in benzene to afford 724 (83JA3273). An alternative rearrangement process can take place upon photolysis of 724 to give 725. Mesylation of 4-(3-hydroxypropyl)-2,4,6-trimethyl-2,5-cyclohexadiene-l-one (78JA4618) and subsequent treatment with sodium azide in DMF afforded the respective azide 726 which underwent intramolecular cycloaddition to afford the triazoline 727 (83JOC2432). Irradiation of 727 gave the triazole derivative 728 (Scheme 126). 

The diazepines 13 react with dimethyl acetylenedicarboxylate to yield mixtures of the pyrazole 19 and the benzene derivatives 18. The reaction proceeds by cycloaddition to yield 14, followed by valence isomerization to the 1,2-diazonines 15, a further valence isomerization to 16, a Second cycloaddition to give 17 and, finally, fragmentation."... 

Treatment of 1,2,4-triazines 91a-91e with the electron-deficient die-nophile dimethyl acetylenedicarboxylate gave products, depending on the substituents [77LA( 10) 1718]. Pyrrolo-[2, -/][ ,2,4]triazines 92 were obtained via [4 + 2]-cycloaddition [77LA(9)1413, 77LA( 10)1718] with 91, but interaction with 91b in the absence of solvent gave, in addition to 92, the pyrido[2,l-/][l,2,4]triazine 93 and [l,3]oxazino[2,3-/][l,2,4]-triazine 94. In case of 91a pyridine and benzene derivatives were also formed in addition to 92 (Scheme 23). 

The reaction of alkoxyarylcarbene complexes with alkynes mainly affords Dotz benzannulated [3C+2S+1C0] cycloadducts. However, uncommon reaction pathways of some alkoxyarylcarbene complexes in their reaction with alkynes leading to indene derivatives in a formal [3C+2S] cycloaddition process have been reported. For example, the reaction of methoxy(2,6-dimethylphenyl)chromium carbene complex with 1,2-diphenylacetylene at 100 °C gives rise to an unusual indene derivative where a sigmatropic 1,5-methyl shift is observed [60]. Moreover, a related (4-hydroxy-2,6-dimethylphenyl)carbene complex reacts in benzene at 100 °C with 3-hexyne to produce an indene derivative. However, the expected Dotz cycloadduct is obtained when the solvent is changed to acetonitrile [61] (Scheme 19). Also, Dotz et al. have shown that the introduction of an isocyanide ligand into the coordination sphere of the metal induces the preferential formation of indene derivatives [62]. 

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