Barbier reactions, samarium iodide

Barbier reaction Samarium(II) iodide, 270 Benzoannelation Chromium carbene complexes, 82 Dicarbonylcyclopentadienylcobalt, 96 Ethyl (Z)-3-bromoacryIate, 130 Grignard reagents, 138 Methyl acrylate, 183 Methyllithium, 188 Ruthenium(III) chloride, 268 Benzoin condensation Benzyltriethylammonium chloride, 239 3-EthyIbenzothiazolium bromide, 130 Benzoylation (see also Acylation) Cadmium, 60 Dibutyltin oxide, 95 Birch reduction Birch reduction, 32... 

Reductive coupling of dialdehydes may also be accomplished by use of samarium(II) iodide514. The reactions is stereoselective and has been used to prepare myo-inositol derivatives (equation 132)515. The equivalent reaction, using low-valent titanium species as catalysts, results in a mixture of products516. The production of cyclic /1-amino alcohols may be accomplished in good yields, and with a high degree of cis selectivity by the treatment of carbonyl hydrazones with samarium(II) iodide (equation 133)517. This reaction is effectively equivalent to an aza-Barbier reaction. 

Samarium iodide has been used to bring about reductive photo-dehalogenation of 1,1-dichlorocyclopropane. The results and the efficiency of the reaction are shown in Scheme 5. The process, a Barbier reaction, is brought about using visible light. The yields of product are enhanced by the addition PhSH as a hydrogen donor. 

In 1980 we noticed that a samarium Barbier reaction between n-butyl iodide and 2-octanone which needed 8 h at 65 °C could be run in 3 h at room temperature in the presence of a catalytic amount (2 mol%) of ferric chloride [15]. This experiment was inspired by the known catalytic effect of the Fe3+ ion on the Ln2+/Ln3+ conversion [146]. The beneficial influence of the Fe(III) derivative in reactions mediated by Sml2 has been used by several authors in various processes. Thus, Molander et al. described a general procedure for five- and six-mem-bered ring annulation starting from 2-(oo-iodoalkyl) cycloalkanones [ 147]. 

Note that there are several modern versions of the Barbier reaction that use transition metals or their derivatives.Examples include indium metal, samarium iodide, and lead. An example using lead reacted benzaldehyde with allyl bromide in the presence of lead metal to give a 99% yield of 45.56 A retro-Barbier fragmentation has also been reported in which an alcohol was treated with 10 equivalents of bromine and 15 equivalents of potassium carbonate in chloroform to give a bromo ketone.5 ... 

Suzuki reported the use of a Grob fragmentation as a step in the conversion of benzocyclobutenols into substituted naphthols. Beginning with indanone 37, samarium iodide-induced Barbier reaction yields tricycle 38 which fragments under the reaction conditions to yield naphthol 39. ... 

Molander, G. A., McKie, J. A. A facile synthesis of bicyclo[m.n.1]alkan-1-ols. Evidence for organosamarium intermediates in the samarium(ll) iodide promoted intramolecular Barbier-type reaction. J. Org. Chem. 1991,56,4112-4120. 

Molander, G. A., Le Huerou, Y., Brown, G. A. Sequenced Reactions with Samarium(ll) Iodide. Sequential Intramolecular Barbier Cyclization/Grob Fragmentation for the Synthesis of Medium-Sized Carbocycles. J. Org. Chem. 2001,66,4511-4516. 

Samarium(n) iodide-promoted intramolecular Barbier-type reactions have also been employed to produce a multitude of cyclic and bicyclic systems. Molander and McKie have enployed an intramolecular Barbier-type reductive coupling reaction to promote the formation of bicyclo[/n.n. l]alkan-l-ols from the corresponding iodo ketone substrates in good yield (eq 15). ... 

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