6 + 4 Cycloaddition
The 6 + 4 cycloaddition is a chemical reaction in which a six-membered ring and a four-membered ring combine to form a new six-membered ring. This reaction is a type of cycloaddition, a process in which multiple unsaturated molecules join together to form a cyclic product. The 6 + 4 cycloaddition is an important synthetic tool in organic chemistry for constructing complex ring systems.
3 Key excerpts on "6 + 4 Cycloaddition"
eBook - ePub- Michael North(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
...These two diastereomers arise from the two possible orientations in which the diene and alkene can react suprafacially as shown in Scheme 9.32 for the reaction between cyclopentadiene and maleic anhydride. Scheme 9.32 Generally, the endo -isomer is the kinetic product of a Diels–Alder reaction despite the fact that it is the thermodynamically less stable product and is formed through the most sterically hindered transition state. The transition state leading to the endo -product is, however, often stabilized by favourable interactions between molecular orbitals not directly involved in the Diels–Alder reaction; these are shown by filled grey orbitals in Scheme 9.32. Such interactions are called secondary orbital interactions. The Diels–Alder reaction is, however, reversible and if it is carried out under thermodynamic control then the exo -isomer can be obtained. 9.6.2 1,3-dipolar cycloadditions In the Diels–Alder reaction, the 4 π electrons are provided by the four atoms of a diene. There are a number of species, however, which contain 4 π electrons distributed over just three atoms: examples include ozone 9.39 and diazo-methane 9.40. This type of compound is called a 1,3-dipole and they undergo [4π + 2π] cycloaddition reactions in exactly the same way (suprafacial with respect to both components) as a diene but give a product containing a five-rather than six-membered ring. The allyl anion 9.41 although not a 1,3-dipole also contains 4 π electrons spread over three atoms and undergoes cycloaddition reactions with alkenes. 9.6.3 [2π + 2π] cycloaddition reactions The cycloaddition reaction between two alkenes (or related species such as ketones) is referred to as a [2π + 2π] cycloaddition reaction since each of the components contributes two π -electrons to the reaction...
eBook - ePubResearch Methodology in Chemical Sciences
Experimental and Theoretical Approach
- Tanmoy Chakraborty, Lalita Ledwani, Tanmoy Chakraborty, Lalita Ledwani(Authors)
- 2017(Publication Date)
- Apple Academic Press(Publisher)
...Recent advances in [2+2+2] cycloaddition reactions. Chem. Soc. Rev. 2011, 40, 3430–3444; (b) Anderson, E. D.; Boger, D. L. Inverse electron demand diels alder reactions of 1,2,3-triazines: pronounced substituent effects on reactivity and cycloaddition scope. J. Am. Chem. Soc. 2011, 133, 12285–12292; (c) Lopez, F.; Mascarenas, J. L. Recent developments in gold-catalyzed cycloaddition reactions. Beilstein J. Org. Chem. 2011, 7, 1075–1094; (d) Moulay, S.; Touati, A. Cycloaddition reactions in aqueous systems: a two-decade trend endeavour. C. R. Chimie. 2010, 13, 1474–1511; (e) Xu, D. Q.; Xia, A. B.; Luo, S. P.; Tang, J.; Zhang, S.; Jiang, J. R.; Xu, Z. Y. In situ enamine activation in aqueous salt solutions: highly efficient asymmetric organocatalytic diels–alder reaction of cyclohexenones with nitroolefins. Angew. Chem. Int. Ed. 2009, 48, 3821–3824; (f) Youcef, R. A.; Dos Santos, M.; Roussel, S.; Baltaze, J. P.; Lubin-Germain, N.; Uziel, J. Huisgen cycloaddition reaction of C-alkynyl ribosides under micellar catalysis: synthesis of ribavirin analogues. J. Org. Chem. 2009, 74, 4318–4323; (g) Meldal, M.; Tornoe, C. W. Cu-catalyzed azide-alkyne cycloaddition. Chem. Rev. 2008, 108, 2952–3015. 2. (a) Erhard, T.; Ehrlich, G.; Metz, P. A. Total synthesis of (±)-codeine by 1,3-dipolar cycloaddition. Angew. Chem. Int. Ed. 2011, 50, 3892–3894; (b) Chen, D.; Wang, Z.; Li, J.; Yang, Z.; Lin, L.; Liu, X.; Feng, X. Catalytic asymmetric 1,3-dipolar cycloaddition of nitrones to alkylidene malonates: highly enantioselective synthesis of multisubstituted isoxazolidines. Chem. Eur. J. 2011, 17, 5226–5229; (c) Kissane, M.; Maguire, A. R. Asymmetric 1,3-dipolar cycloadditions of acrylamides. Chem. Soc. Rev. 2010, 39, 845–883; (d) Stanley, L. M.; Sibi, M. P. Enantioselective copper-catalyzed 1,3-dipolar cycloadditions. Chem. Rev. 2008, 108, 2887–2902; (e) Kamata, K.; Nakagawa, Y.; Yamaguchi, K.; Mizuno, N...
- Ahindra Nag, Ahindra Nag(Authors)
- 2018(Publication Date)
- CRC Press(Publisher)
...Then, the naphthyl group of the catalyst shields the bottom face of the alkyne (Figure 11.13). FIGURE 11.13 Formal Diels–Alder/Michael addition organocascade reaction. Once the formal Diels–Alder took place, the cycloadduct 79 undergoes an easy β-elimination of the methyl selenide to render the unsaturated iminium ion 80. Next, the pendant BOC imine reacts with the double bond via a Michael addition to furnish the cis-fused bicyclic ring. After hydrolysis, the tetracyclic ring 72 was obtained with good yield and excellent enantioselectivity (82% yield, 97% ee). Decarbonylation using Wilkinson’s catalyst and treatment with phosgene and methanol introduce the carbomethoxy group at the dienamine position. Next, treatment with DIBAL-H reduces the unsaturated enamine to install the tertiary indoline stereocenter and provides the unsaturated ester. Finally, the treatment with trifluoroacetic acid deprotects the BOC amine and generates compound 85 (Scheme 11.18). SCHEME 11.18 Synthesis of compound 85. Intermediate 85 was converted into the vinyl iodide 87 using a two-step protocol. First, an allylation with allylbromide takes place, followed by reduction with DIBAL-H to furnish the diol 87 (Scheme 11.19). SCHEME 11.19 Synthesis of compound 87. Compound 87 is then converted to the protected Wieland–Gumlich aldehyde 90 through a Jeffery–Heck cyclization sequence (Scheme 11.20). First, Pd inserts in the vinyl iodide and subsequent carbopalladation forms the six-membered ring and an alkyl palladium intermediate that undergoes a fast β-elimination to form the enol intermediate...
