Samarium iodide, with

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). 

Zard and coworkers have developed a synthesis of substituted dienes by reductive elimination of allylic nitroacetates (equation 33)66. Allylic nitroacetates can be prepared by condensation of nitromethane with the carbonyl compound followed by addition of formaldehyde and acetylation67. Reductive elimination can be carried out by employing either chromous acetate or samarium iodide. 

When 1,2-dihydroquinazolines are actually desired as the reaction product, they can often be contaminated with their conjugated analogs due to spontaneous dehydrogenation <2000JME4479>, but this can be avoided under reductive conditions, as demonstrated by the preparation of 2-substituted-l,2-dihydroquinazolines 815 by the reductive condensation of 2-nitrobenzamides 814 with aldehydes in the presence of samarium iodide <2002JHC1271>. 

Samarium iodide-induced radical reaction of di(2-nitrophenyl)disulfides with ot-bromoketones has also been reported (Scheme 65) <2001HAC156, 2001TL3125>. 

Oxindoles are prepared using a solid-phase Pummerer reaction. Thus, the immobilized amide 182 undergoes the Pummerer rearrangement on treatment with TFAA and boron trifluoride diethyl etherate (BF3 Et20) (Equation 118). Cleavage of the oxindole from the linker is achieved using samarium iodide and 1,3-dimethyl-3,4,5,6-tetrahydro-2(lH)-pyrimidinone (DMPU) <2003CC2380>. 

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>. 

There are extensive possibilities for the formation of geometric and optical isomers in eight-coordinate complexes. Thus far. apparently only one pair has been completely characterized The diglyme [= di(2-methoxyethyl)etherl adduct of samarium iodide. Sml rO(CH2CH2OCH3)2]2. has been isolated in both cis and irons forms. The trans complex (Fig. 12.39a) has a center of symmetry Thus, the I—Sm—1 angle is exactly 180. and the molecule is a bicapped trigonal antiprism. The cis isomer (Fig. (2.39b) has ihe lower symmetry of a distorted dodecahedron with I—Sm—I angles of 92 > ... 

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

Thus, this method takes advantage of a relatively rapid 9-endo-trig cyclization, rather than undergoing other possible reactions with samarium iodide [32],... 

Allyl acetates can also be reduced by Pd° catalysts in conjunction with samarium iodide,303 model NAD(P)H compounds306 and under electrochemical conditions (equations 107 and 108).307... 

Appropriate functionalization of C=N bonds can greatly assist their asymmetic reduction. In particular, the reduction of N-acyl hydrazones with a rhodium complex of the ligand DuPHOS (P13) represents an outstanding example. In this process (Scheme 62) a product of up to 97% e.e. is obtained in high yield. After the reduction, samarium-iodide cleavage of the N—N bond gives the product amine273,274. 

The 4,7-dimethoxy-2,2-dimethyl-l,3,2-benzodiselenastannole 321 was prepared from commercially available 1,4-dimethoxybenzene 320 by a sequence of tandem ortho-lithiation and selenation, and followed by dimethyltin protection in 28% yield (Scheme 51). Then, sequential treatment of the stannole 321 in THF with selenyl chloride, trimethylsilyl trifluoromethanesulfonate (TMSOTf), and samarium iodide gave crystalline 4,7-dimethoxybenzotri-selenole 42 in 75% yield <1996H(43)1843>. The structure was characterized by X-ray crystallographic analysis (Section 6.12.3.1). 

But how else might they have done it Perhaps equally obvious is to use the pinacol reaction to make the diol 68 and oxidise both alcohols. We shall now broaden the discussion by writing Ar for the substituents as many of the reactions have not in fact been done with o-tolyl substituents. Two of the best yielding methods are Mg in the presence18 of Me3SiCl and samarium iodide where the colour change from blue Sm(III) to yellow Sm(IL) is characteristic.19... 

Reduction of A,(V-di bcnzy lam i noalkyl chloromethyl ketones 133, followed by spontaneous intramolecular ring closure of the resulting 7-chloroamines 134, afforded azetidinium salts 135, which were subsequently deprotected toward chiral 3-hydroxyazetidines 136 and 137 (Scheme 29) <1997JOC1815>. In a similar approach, ct-amino aldehydes 138 were converted into 3-hydroxyazetidinium salts 139 upon treatment with diiodomethane and samarium iodide, followed by stabilization using AgBF4. Ar-Dealkylation with Pd afforded enantiopure azetidines 140 (Scheme 30) <2000TL1231>. 

The amides derived from /3-hydroxy-a-amino acids, obtained from the reaction of the latter with resin-bound hydroxylamine, have been cyclized under the Mitsunobu conditions to afford 3-aminoazetidin-2-ones. The free azetidin-2-ones were cleaved from the resin by reduction with samarium iodide <20010L337>. 

Thus cyclopentene reacts with tribromomethyl phenyl sulfone to give a high yield of addition product (equation 106). Samarium iodide catalysis gives a good yield of addition product upon reaction of l-chloro-2-iodoethanes with 1-alkenes (equation 107)690. The product from this reaction has been used to prepare a cyclic target molecule in several further steps. a-Bromoesters also undergo a similar reaction, the product from which upon treatment with KOH gives lactones directly. 

In the stereoselective synthesis of epothilone A (11), Carreira used a syn -reduction methodology in the synthesis of the key intermediate (14)9 (Scheme 4.If). Reduction of the isoxazoline 12 with samarium iodide at 0 C in THF gave the ketone 13. Narasaka reduction of the P-hydroxy ketone 13 using triethylb-orane/sodium borohydride afforded the. syn-diol 14 in high yield and with high diastereoselectivity. 

The furan-fused 1,2-oxazocine 126 cleaved the N-O bond when treated with NaBH4 catalyzed by Mo(CO)6 to give the furan 127 (Equation 6). It is noteworthy that hydrogenation conditions, such as activated zinc and samarium iodide, failed to cleave the N-O bond <2005JOC6995>. 

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... 

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