Addition and cycloaddition reactions

6-Diphenylthieno[2,3-c]furan (130) reacted with 7V-4-methylphenylmaleimide at room temperature to give in 73% yield endo adduct (131). In the presence of 4-methylbenzenesulfonic acid the substituted benzo[6]thiophene derivative (132) was obtained. Vinylene carbonate as dienophile led to an endo/exo mixture (133a) and (133b) in the ratio 6 1. The same reaction in the presence of sulfuric and acetic acids afforded compound (134) 89CB1U9). 

The reaction of 3-phenyl-4-benzoylselenolo[3,4-6]indole (135) and DMAD afforded dimethyl 9-benzoyl-l-phenylcarbazole-2,3-dicarboxylate (136) 82JHC227 . 

3-(l-Hydroxy-6-hepten-l-yl)thiophene-2-carbaldehyde (143) under reflux with AcOH gave the 

The syntheses and Diels-Alder reactions of 5//-thieno[2,3-c]pyrrole (17) as well as benzo and Aralkyl derivatives of furo[2,3-c]pyrrole (22) have been described by Sha et al. 86CC310, 88CC1081, 90JOC2446, 95T193). 

Thieno[3,4-c]thiophenes have been the subject of chemical investigations since the early 1970s 1996CHEC-11(7)1 . Despite this interest, only a few isolable compounds of this class have been prepared. 

The unstable l,3-bis(methoxycarbonyl)selenolo- 190 and l,3-bis(methoxycarbonyl)tellurolo[3,4-f]thiophene 191 underwent Diels-Alder reaction with DMAD to produce cycloadducts, which lost selenium or tellurium and collapsed to tertracarbomethoxybenzo[f]thiophene 192 in low yields 20020L1193 . 

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The functionalized allene, DIMETHYL 2,3-PENTADIENEDIOATE, the first in the series, is an intriguing substrate for various addition and cycloaddition reactions. Finally, a new reagent, DI-ferf-BUTYL DICARBONATE, for he formation of A-f-BOC derivatives which eliminates the use o the hazardous fert-BUTYL AZIDOFORMATE (WARNING) is intrqduced. 

The synthesis of iminosilanes has opened up a new field of silicon-nitrogen chemistry. These compounds have an interesting chemistry. As shown, many addition and cycloaddition reactions are possible. Many new and surprising results are likely in the future. 

Misumi, S. Recognitory Coloration of Cations with Chromoacerands. 165, 163-192(1993). Mizuno, K., and Otsuji, Y. Addition and Cycloaddition Reactions via Photoinduced Electron Transfer. 169, 301-346 (1994). 

The ability of nitrile oxides to undergo addition and cycloaddition reactions makes it possible to use them in polymer chemistry and technology. Major trends might be synthesis, modification, cross-linking of polymers, addition of nucleophiles, and 1,3-dipolar cycloaddition of nitrile oxides. Taking into account the scarcity of reviews devoted to this topic, not only recent but also previous references will be cited in this subsection. 

The disilagermirenes shown in Equation (190) react rapidly with SnCl2 to give the disilagermastannetene as orange crystals, with 5119Sn = 439.3, which is indefinitely stable in solution and in the solid state. The Sn=Ge bond readily undergoes addition and cycloaddition reactions, and, with carbon tetrachloride, the tetrachloro derivative is formed.582... 

Addition and Cycloaddition Reactions via Photoinduced Electron Transfer... 

Considered in this section are two groups of oxepine reactions (1) addition and cycloaddition reactions peculiar to their conjugated carbon chain, and (2) those characteristic of vinyl ethers, particularly, beginning from an attack on ring oxygen. Both reaction types are discussed in detail in CHEC(1984) and CHEC-II(1996) therefore, only several important new examples are given here. 

Under certain circumstances, the conjugate addition and cycloaddition reaction pathways overlap for a,P-unsaturated electrophiles. For example, when the 2,5-dimethylpyrrole complex 22 is combined with 1 equiv of MVK in acetonitrile, a 1 1 ratio of the p-alkylated 3//-pyrrole complex 96 and the a-alkylated 2Z/-pyrrole complex 98 is isolated (Figure 18). When the reaction is monitored by H NMR in CD3CN, an intermediate 7-azabicyclo[2.2.1]heptene complex (97) is observed at early reaction times, and eventually converts (tm 1 h) to compound 98 via a retro-Mannich reaction followed by proton transfer. 

The rearrangement could be corroborated via addition and cycloaddition reactions and also by the synthesis of the (OC)5 V=SnRR, complex97. The analogous chromium complex is formed via a reaction of chromium hexacarbonyl in THF (Scheme 16)98. The molecular structure is shown in Figure 42. The molybdenum complex is formed in the same way (Scheme 16, Figure 43)98. 

Kira and coworkers recently reported their extensive investigations on addition and cycloaddition reactions of the tetrasilyldisilene 16 and described not only expected reactions but also some surprising results69. These reactions are summarized in Scheme 1. 

SCHEME 1. Some addition and cycloaddition reactions of disilene 16... 

In spite of their bulky substituents, the presence of which is necessary to prevent oligomerization reactions, disilenes undergo numerous addition and cycloaddition reactions these have been summarized in several review articles [1]. For example, stable or marginally stable disilenes react with the C=0 and C=S groups of ketones [2-4] and thioketones [5] as well as with the triple bonds of acetylenes [2, 3] and nitriles [6]. Surprisingly, however, no cycloaddition reactions of disilenes with simple alkenes have yet been reported [1]. 

Terminal chalcogenido zirconium complexes (23) are conveniently synthesized by the reactions of dicarbonylzir-conocene with either N2O or the elemental chalcogens (S, Se, Te) see Chalcogens) in the presence of pyridine. The Zr=E bond in these complexes is highly reactive and leads to a variety of 1,2-addition and cycloaddition reactions (Scheme 8). ... 

This review article deals with addition and cycloaddition reactions of organic compounds via photoinduced electron transfer. Various reactive species such as exdplex, triplex, radical ion pair and free radical ions are generated via photoinduced electron transfer reactions. These reactive species have their characteristic reactivities and discrimination among these species provides selective photoreactions. The solvent and salt effects and also the effects of electron transfer sensitizers on photoinduced electron transfer reactions can be applied to the selective generation of the reactive species. Examples and mechanistic features of photoaddition and photocycloaddition reactions that proceed via the following steps are given reactions of radical cations with nucleophiles reactions of radical anions with electrophiles reactions of radical cations and radical anions with neutral radicals radical-radical coupling reactions addition and cycloaddition reactions via triplexes three-component addition reactions. 

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