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Samarium II Mediated Radical Reactions

The present contribution attempts to focus on those radical processes in which Sml2 provides unique advantages over more traditional reductants. Because of the prodigious number of publications describing the use of Smli in promoting radical reactions, a comprehensive review is not possible. However, an attempt has been made to highlight those processes deemed synthetically among the most valuable or unique. [Pg.153]

2 Alkyl, Aryl, and Alkenyl Radical Addition Reactions [Pg.153]

The persistence of carbon-centered radicals is based on many factors. In a reductive medium, wherein the radicals are generated from halides or related substrates, one of the most important elements is the rate at which the radical is further reduced ( redn) (Eq. 1). Thus there is an inherent competition between the desired radical process ( rad) leading to radical product P and kredn [3]. In elegant mechanistic studies, the details of electron transfer and the relative rate constants for the reduction of primary alkyl radicals by Sml2 have been determined [4]. In THF/ HMPA, for example, the rate constant for the reduction of a primary alkyl radical [Pg.153]

The initial radical addition reactions can also be sequenced with a second, nucleophilic reaction. Thus radical conjugate addition and subsequent reduction leads to an enolate. Enolates thus generated can undergo a variety of reactions [8] including aldol reactions [9], Claisen condensations, intramolecular Michael reactions, and intermolecular Tischenko redox processes (Eqs. 7, 8). [Pg.155]

A series of substrates has been investigated that pits 5-exo cyclization versus [Pg.155]


Molander, G.A. (2001) Samarium(II) mediated radical reactions. In P. RenaudandM.P. Sibi (Eds) Radicals in Organic Synthesis (vol 1). Wiley-VCH, Weinheim, pp. 153-82. [Pg.292]

The occurrence of the indole subunit is well established within the class of natural products and pharmaceutically active compounds. Recently, the Reissig group developed an impressive procedure for the assembly of highly functionalized in-dolizidine derivatives, highlighting again the versatility of domino reactions [8]. The approach is based on a samarium(II) iodide-mediated radical cydization terminated by a subsequent alkylation which can be carried out in an intermolecular - as well as in an intramolecular - fashion. Reaction of ketone 3-11 with samarium(ll) iodide induced a 6-exo-trig cydization, furnishing a samarium enolate intermediate... [Pg.224]

Intramolecular addition of vinyl radicals to olefins as a method for heterocycle synthesis has been examined. The vinyl radicals can be conveniently generated from vinyl bromides and samarium(II) diiodide [95JOC7424], The intermediate radical after cyclization undergoes a further electron transfer from samarium to furnish a carbanion which is quenched at the end of the reaction. A samarium(II) diiodide mediated aryl radical cyclization onto a dihydrofuran has been reported [95T8555],... [Pg.20]

Ni(0) catalyst. A radical 5-exo cyclization to the potentially zinc or nickel-complexed ketone provides an alkoxyl radical that combines with the co-produced Ni(I) species. A transmetalation to a zinc alkoxide regenerates the catalyst and forms the zinc cyclopentoxide, from which products 79 are liberated on hydrolysis. A bimetallic Cu(I)-Mn(II) system provided similar results (see Sect. 8.4). Analogous samarium diiodide-mediated reactions require in contrast stoichiometric amounts of the reducing agent and are less diastereoselective [26, 27],... [Pg.349]


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