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1 Introduction Asymmetric 1,3-Dipolar Cycloadditions Of UCC Library and UCC researchers have made this item openly available. Please let us know how this has helped you. Thanks! Title Asymmetric 1,3-dipolar cycloadditions of acrylamides Author(s) Kissane, Marie; Maguire, Anita R. Publication date 2009 Original citation KISSANE, M. & MAGUIRE, A. R. 2010. Asymmetric 1,3-dipolar cycloadditions of acrylamides. Chemical Society Reviews, 39, 845-883. doi:10.1039/B909358N Type of publication Review Link to publisher's http://pubs.rsc.org/en/content/articlelanding/2010/cs/b909358n version http://dx.doi.org/10.1039/B909358N Access to the full text of the published version may require a subscription. Rights ©2010, The Authors. Exclusive licence to publish RSC Publishing. Item downloaded http://hdl.handle.net/10468/593 from Downloaded on 2021-10-06T13:25:14Z 1 Introduction Asymmetric 1,3-Dipolar Cycloadditions of Acrylamides Marie Kissanea and Anita R. Maguireb* a Department of Chemistry, Analytical and Biological Chemistry Research Facility, University College Cork, Cork, Ireland. bDepartment of Chemistry & School of Pharmacy, Analytical and Biological Chemistry Research Facility, University College Cork, Cork, Ireland. *Corresponding author. Tel.: +353 21 4901693; fax: +353 21 4274097. E-mail: [email protected]. Contents 1 Introduction ........................................................................................................................................................ 1 1.1 1,3-Dipolar cycloadditions ..................................................................................................................... 2 1.1.1 The 1,3-Dipole ..................................................................................................................................... 2 1.1.2 The Dipolarophile ................................................................................................................................ 4 1.1.3 Mechanism of 1,3-Dipolar Cycloaddition ........................................................................................... 5 1.1.4 Regioselectivity of 1,3-Dipolar Cycloaddition .................................................................................... 6 1.1.5 Stereoselectivity................................................................................................................................... 7 1.1.6 Reactivity ............................................................................................................................................. 8 1.2 Asymmetric 1,3-Dipolar Cycloadditions .............................................................................................10 1.2.1 Cycloadditions with Nitrile Oxides ....................................................................................................13 1.2.1.1 Synthesis of Nitrile Oxides .......................................................................................................14 1.2.1.2 Regioselectivity .........................................................................................................................14 1.2.1.3 Asymmetric 1,3-Dipolar Cycloaddition of Nitrile Oxides .......................................................15 1.2.1.4 Asymmetric 1,3-Dipolar Cycloadditions of Nitrile Oxides and Acrylamides .........................16 1.2.2 Cycloadditions with Nitrones .............................................................................................................26 1.2.2.1 Synthesis of Nitrones ................................................................................................................26 1.2.2.2 Regioselectivity .........................................................................................................................27 1.2.2.3 Stereochemistry ........................................................................................................................28 1.2.2.4 Asymmetric 1,3-Dipolar Cycloadditions of Nitrones...............................................................29 1.2.2.5 Asymmetric 1,3-Dipolar Cycloadditions of Nitrones and Acrylamides ..................................30 1.2.2.5.1 Non-Metal Catalysed Cycloadditions ...................................................................................30 1.2.2.5.2 Metal Catalysed Cycloadditions...........................................................................................37 1.2.2.5.2.1 Titanium Catalysts ........................................................................................................39 1.2.2.5.2.2 Magnesium Catalysts ....................................................................................................41 1.2.2.5.2.3 Manganese Catalysts .....................................................................................................43 1.2.2.5.2.4 Zinc Catalysts................................................................................................................43 1.2.2.5.2.5 Copper Catalysts ...........................................................................................................44 1.2.2.5.2.6 Palladium Catalysts .......................................................................................................45 1.2.2.5.2.7 Nickel Catalysts ............................................................................................................46 1.2.2.5.2.8 Lanthanide Catalysts .....................................................................................................48 1.2.3 Cycloadditions with Diazoalkanes......................................................................................................48 1.2.3.1 Regioselectivity and Reactivity .................................................................................................49 1.2.3.2 Asymmetric 1,3-Dipolar Cycloadditions of Diazoalkanes and Acrylamides ..........................50 1.2.4 Cycloadditions with Azomethine Ylides ............................................................................................55 1.2.4.1 Synthesis of Azomethine Ylides ...............................................................................................56 1.2.4.2 Reactivity and Regioselectivity .................................................................................................57 1.2.4.3 Asymmetric 1,3-Dipolar Cycloadditions of Azomethine Ylides ..............................................58 1.2.4.4 Asymmetric 1,3-Dipolar Cycloadditions of Azomethine Ylides and Acrylamides ..................58 1.2.5 Cycloadditions with other 1,3-Dipoles ...............................................................................................64 1.2.5.1 Allyl Anion Type Dipoles .........................................................................................................64 1.2.5.2 Allenyl/Propargyl Anion Type .................................................................................................66 1.3 Conclusion ..............................................................................................................................................67 1.4 References ..............................................................................................................................................67 1.1 1,3-Dipolar cycloadditions 1,3-Dipolar cycloadditions offer a very useful method for the preparation of five- membered ring heterocycles.1,2 This [4s + 2s] cycloaddition, thermally allowed by the Woodward-Hoffmann rules,3 involves the reaction of a dipolarophile (e.g. alkenes, alkynes, carbonyls and nitriles) with a 1,3-dipolar compound (Scheme 1). The concept of 1,3-dipolar cycloadditions was initially suggested by Smith in 1938,4 but it was only after the generalisation of the reaction by Huisgen in the 1960’s that the reaction became widely applicable.5 The research conducted in the area of 1,3-dipolar cycloadditions has been immense over the past 40 years,6-45 and the reaction is now utilised in almost every area of chemistry, from materials chemistry46 to drug discovery,47 indicating its diversity. Scheme 1 1.1.1 The 1,3-Dipole The 1,3-dipole is a three-atom -electron system, with four -electrons delocalised over the three atoms. It can be represented by two octet-structures, in which the positive charge is located on the central atom and the negative charge is distributed over the two terminal atoms, and two sextet-structures, wherein two of the four -electrons are localised at the central atom (Scheme 2). The sextet formulas contribute little to the electron distribution of the resonance hybrid but illustrate the ambivalence of the 1,3-dipole, which is key to understanding the mechanism, reactivity and regiochemistry of 1,3-dipolar cycloadditions. Scheme 2 1,3-Dipoles can be classified into two types; the allyl anion type (so-called because it is isoelectronic with the allyl anion) and the propargyl/allenyl anion type. The allyl anion type is characterised by four electrons in three parallel pZ orbitals perpendicular to the plane of the dipole. 1,3-Dipoles of the allyl type are bent, while the presence of a double bond orthogonal to the delocalized -system in the propargyl/allenyl anion type confers linearity to the dipole (Scheme 3). Scheme 3 For the allyl type dipoles, the central atom b may be a group V element (e.g. N or P) or a group VI element (e.g. O or S). For the propargyl/allenyl types, the role of b is restricted to group V elements, as only an atom of this group can bear a positive charge in the quartervalent state. By restricting a and c to second-row elements (C, N, O),
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