Carbon diiodide

As another possibility for introducing a double bond in the alkylation step, the intermediate aldehyde can be olefinated in the presence of carbon diiodide [57]. When iodo mannopyranoside 64 was treated with zinc, CH2I2, TMSCl, and PbCl2, diene 56a was obtained (Scheme 3.22) [37]. Since there are no stereocenters generated in this transformation, it is a better method for preparing diene 56a than the elimination-vinylation reaction (Section 1.2, Scheme 3.18). 

Formation of the /3-lactam (161) by reaction of the dianion (160) with methylene diiodide provides an example of a [3 + 1] type of ring closure (79TL2031). The insertion of carbon... 

Compound 9 has been prepared by the latter authors using triethylene glycol diiodide and triethylene glycol diamine (see Eq. 4.11) and an alkali metal carbonate in acetonitrile solution. ... 

The mechanism for the transformation of 5 to 4 was not addressed. However, it seems plausible that samarium diiodide accomplishes a reduction of the carbon-chlorine bond to give a transient, resonance-stabilized carbon radical which then adds to a Smni-activated ketone carbonyl or combines with a ketyl radical. Although some intramolecular samarium(n)-promoted Barbier reactions do appear to proceed through the intermediacy of an organo-samarium intermediate (i.e. a Smm carbanion),10 ibis probable that a -elimination pathway would lead to a rapid destruction of intermediate 5 if such a species were formed in this reaction. Nevertheless, the facile transformation of intermediate 5 to 4, attended by the formation of the strained four-membered ring of paeoniflorigenin, constitutes a very elegant example of an intramolecular samarium-mediated Barbier reaction. 

Samarium diiodide is another powerful one-electron reducing agent that can effect carbon-carbon bond formation under appropriate conditions.257 Aromatic aldehydes and aliphatic aldehydes and ketones undergo pinacol-type coupling with Sml2 or SmBr2. 

Burk et al. showed the enantioselective hydrogenation of a broad range of N-acylhydrazones 146 to occur readily with [Et-DuPhos Rh(COD)]OTf [14]. The reaction was found to be extremely chemoselective, with little or no reduction of alkenes, alkynes, ketones, aldehydes, esters, nitriles, imines, carbon-halogen, or nitro groups occurring. Excellent enantioselectivities were achieved (88-97% ee) at reasonable rates (TOF up to 500 h ) under very mild conditions (4 bar H2, 20°C). The products from these reactions could be easily converted into chiral amines or a-amino acids by cleavage of the N-N bond with samarium diiodide. 

Novel synthetic procedures for indolizidine alkaloids were developed via a samarium diiodide-promoted carbon-nitrogen bond cleavage as a key step. Application of the procedure led to the total synthesis of (+)-(8R, 8aR)-perhydro-8-indolizidinol <2006H193>. 

First, the methods that apply to all three trihalides are reviewed then other specific methods are mentioned. Far fewer methods have been perfected for preparing anhydrous lanthanide tribromides than for the trichlorides, though most of them are similar. The triiodides are the most difficult to prepare, as the iodine analogs of several useful chloro and bromo sulfur and carbon compounds are not known. Reaction temperatures for preparation of triiodides have to be carefully controlled, as Sml3 and Ybl3, for example, decompose easily at elevated temperatures to diiodides. The existence of Eul3 is questionable, with EuI2 formed even at room temperature. 

Palladium-catalyzed a-arylation of ketones is performed with arylene dihalides and bifunctional aromatic ketones 148 to result in the bond formation at the r/) -a-carbon of the ketone, leading to polyketone 149. The reaction is carried out in the presence of Pd(0) and various phosphines. Several bidentate phosphines and bulky alkylphosphines such as dppf, BINAP, PCys, and P Bu3 are shown to be effective, while PPh3 results in no reaction. Arylene dibromide and diiodide are applicable as the co-monomers. The polymerization reaction is carried out in THE in the presence of NaO Bu at 75 °C under N2, and polymers 149 are isolated in 60-80% yields (M = 7000-15 000). Polyketone 149 is further transformed to conjugated polymer PPV by reduction of the ketone moiety with LiAlH4 followed by dehydration with an acid (Equation (69)). 

Into a solution of residue 59 (101 mg, 0.1 mmol) in 20 mL of dry toluene, kept at 60°C, was syringed, during 18 h and under argon, a freshly prepared solution of samarium diiodide in benzene-HMPA (9 1, v/v 6.3 mL, 0.51 mmol) which has been diluted with 3.8 mL of dry benzene. The solvents were distilled off under reduced pressure, and the residue was taken up in 10 mL of diethyl ether. The ether solution was washed with 10% aqueous solution of sodium bisulfite, then water, dried (MgS04), and concentrated. The crude product was dissolved in 1.5 mL of tetrahydrofuran and treated during 30 min at room temperature with 1.5 mL of a 40% aqueous solution of HF. The solution was neutralized with solid sodium carbonate, and concentrated. Flash chromatography on silica gel (cyclohexane-ethyl acetate, 3 1 to 1 2) afforded the product 80 (40.6 mg, 50%), a single isomer, as an amorphous solid. It was characterized by its diacetate [a]D +36° (c 4.0, CHClj). 

Arsenic diiodide crystallises in thin prisms of a deep cherry-red colour. In air they are rapidly oxidised9 and become opaque and brick-red. The crystals, when purified by careful distillation, melt at 130° C., but the undistilled product, as generally prepared, melts at about 120° C. owing to the presence of dissolved arsenic.10 The boiling point10 in an atmosphere of hydrogen or carbon dioxide is 375° to 880° C. 

The crystals dissolve in carbon disulphide and ebullioscopic measurements indicate1 that the molecular formula is As2I4 they also dissolve in ether, alcohol and chloroform. When exposed to air, these solutions darken in colour owing to the formation of the triiodide, and the diiodide cannot be recovered bv evaporation owing to complete decomposition. Boiling acetic anhydride also dissolves the crystals but, on cooling, a yellow substance which appears to contain a derivative of the triiodide separates. The diiodide is also decomposed by pyridine with separation of arsenic, the triiodide being found in solution. 

A. Granger reported Copper diphosphide, CuP2, to be formed when carbon dioxide charged with vapour of phosphorus trichloride, tribromide, or diiodide is passed... 

The observations of C. L. Gazzaniga,1 A. Schrotter, and T. S. Traill were treated in connection with the action of iodine on phosphorus. Some indefinite iodides were mentioned by F. Wohler, J. L. Gay Lussac, C. M. van Dijk, R. Boulouch, K. I. Lissenko, and F. Sestini. The two best defined iodides are the diiodide and triiodide while the existence of the tetritaiodide, the tetratritaiodide, and of the pentaiodide is not so well established. According to R. Boulouch, where dry iodine is added to a soln. of phosphorus in dry carbon disulphide in quantity less than is... 

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