Coupling samarium iodide

Samarium iodide (Sml2) gives the same reaction. Benzoyl chloride was coupled to give benzil by subjecting it to ultrasound in the presence of Li wire 2 PhCOCl -I-... 

It has been shown recently that the selective reductive homo-coupling polymerization of aromatic diisocyanates via one electron transfer promoted by samarium iodide in the presence of hexamethylphosphoramide [PO(NMe2)3] (HMPA) can produce poly(oxamide)s in nearly quantitative yield (Scheme 9). 

Another well-known transformation of carbonyl derivatives is their conversion to pinacols (1,2-diols) via an initial one-electron reduction with highly active metals (such as sodium, magnesium, aluminum, samarium iodide, cerium(III)/ I2, yttrium, low-valent titanium reagents (McMurry coupling), etc.), amines, and electron-rich olefins and aromatics as one-electron donors (D).43 Ketyl formation is rapidly followed by dimerization44 (equation 22). 

O Neill and Helquist have also discovered that 1,10-phenanthroline 48 undergoes samarium iodide-promoted coupling with ketones and this process has been applied to the chiral ketone (—)-thujone 53 to give the corresponding phenanthroline 54 as a single stereoisomer (Equation 5) <19990L1659>. 

A related method involving the samarium iodide-mediated coupling of a-benzoyloxy lactones with ketones has been reported recently by Enholm [164,165]. 

P. Girard, J. L. Namy, and H. B. Kagan, Divalent lanthanide derivatives in organic synthesis. 1. Mild preparation of samarium iodide and ytterbium iodide and their use as reducing or coupling agents,. /. Am. Chem. Soc., 102 (1980) 2693-2698. 

For further applications of samarium iodide promoted ketone-olefin couplings see M. Kawatsura, K. Hosaka, F. Matsuda and H. Shirahama, Synlett, 1995, 729. 

Fluoro- and chloro-substituted tricarbonyl chromium arene complexes can be reductively coupled with ketones, in the presence of samarium iodide, to give tertiary alcohols (Scheme 109). A related reaction of a tethered alkoxyimine furnished a tricyclic compound (Scheme 110). Samarium also promotes the formation of a benzyhc ketyl... 

The chromium-complexed benzylic radicals are also known and were employed in a variety of useful organic reactions. One electron reductive coupling of the tricarbonylchromium complexes of o-substituted benzaldehydes and benzaldi-mines with samarium iodide gave 1,2-diols and diamines, respectively, in good yields with extremely high threo diastereoselectivity (Eq. 7) [7]. Therefore, enantiomerically pure 1,2-diols and diamines were easily obtained by using the planar chiral chromium complexes of benzaldehyde and benzaldimine. 

The intermolecular coupling of imine derivatives and aldehydes can be achieved using samarium iodide. For exatiple. 

Synthesis of Homoenolate Equivalent. The samarium iodide-induced coupling of carbonyl derivatives with methoxyal-lene provides 4-hydroxy 1-enol ethers in high yields (eq 58). An almost equimolar mixture of the two enol ethers are usually observed but acid hydrolysis leads to the aldehyde. 

Other examples involve Mizoroki-Heck couplings of aryl bromides using a sulfur linker cleaved nnder very mild conditions in the presence of samarium iodide [17, 18], the solid-supported hyperbranched polymerization of phenylacetylene derivatives [19] or a... 

Samarium iodide promotes the pinacol homo-coupling of aldehydes to give 1,2-diols, but typically with little difference in the yields of the syn- and anti-isomers. Addition of Lewis acids, however, improves the selectivity, apparently by complex-ing both reactants in the transition state. Chiral aldehydes such 2-phenylpropanal can give syn/anti ratios >50, even without additives, and in some cases they give exclusively one product with appropriate choice of conditions. 

Scheme 3. Samarium iodide mediated coupling reaction between halides, isocyanides and carbonyl substrates to form Q -hydroxyketones.

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