Hydrogen iodide reduction

Hydrogen iodide reduction has recently been used1 also in the steroid field to effect reduction of the 6/V7j -epoxide derivative ehn -n in Eq. (411). 

Hydrogen iodide reduction hes recently been uBed " eleo in the eterdd field to effect reductioD of the J ,7i -epoxide derivetlve ehn .-n inEq.(4U). 

Scheme 98) (523). Hydrogen chloride is unsatisfactory as a cyclizing agent, whereas hydrogen iodide causes further reduction and leads directly to derivatives of the previously inaccessible 4-aminothiazoles (see Section VII. 2). 

Finally, secondary arsines can be obtained by the reductive cleavage of diarsines with mercury and hydrogen iodide (49) or with hthium aluminum hydride... 

This retro-aldol-typc fragmentation is possible because the chlorin chromophore stabilizes the anion formed on loss of the a-oxo acid residue. A related reactivity is observed in the reduction of 3-vinylchlorins, e.g. 24, to 3-ethylporphyrins, e.g. 25, in the presence of hydrogen iodide in acetic acid. The mechanism of this reaction can be represented as a sequence of tautomeric reactions which lead to the completely conjugated porphyrin system.32c-40-54... 

The carbon-chain structure of the sugar obtained from hamameli-tannin was established by the classical method of Kiliani,26 which is based on the reduction, with hydrogen iodide, of polyhydroxy acids to fatty acids. Treatment of the calcium salt of hamamelonic acid under these conditions led to inconclusive results. The reduction of the corresponding, crystalline ammonium salt, however, furnished 3.5 to 5% of 2-methylvaleric acid, which was identified by the properties of its crystalline p-iodophenacyl ester. Thus, it was proved that the sugar must have structure XIV. 

Reaction (9) generates methyl iodide for the oxidative addition, and reaction (10) converts the reductive elimination product acetyl iodide into the product and it regenerates hydrogen iodide. There are, however, a few distinct differences [2,9] between the two processes. The thermodynamics of the acetic anhydride formation are less favourable and the process is operated much closer to equilibrium. (Thus, before studying the catalysis of carbonylations and carboxylations it is always worthwhile to look up the thermodynamic data ) Under standard conditions the AG values are approximately ... 

Similar waves in the cathodic polarogram were observed by Donnet and Henrich 58) using oxidized carbon black. The wave disappeared after treatment with isobutyronitrile. It was assumed that isobutyro-nitrile gives an addition reaction with quinones. No reaction with this reagent was observed after reduction with hydrogen iodide, after treatment with aniline, or after treatment with diazomethane. The latter finding confirms the assumption by Studebaker et al. 38) that diazomethane is added to the quinones in the carbon black surface. 

Milder reductions with hydriodic acid can be accomplished by using more dilute hydriodic acid, or solutions of hydrogen iodide prepared from alkaline iodides and hydrochloric or acetic acid in organic solvents [22S],... 

Reduction of carbonyl to methylene in aromatic ketones was also achieved by (dane prepared from lithium aluminum hydride and aluminum chloride [770], by soditim borohydride in triiluoroacetic acid [841 with triethylsilane in trifluoroacetic acid [555, 777], with sodium in refluxing ethanol [842], with zinc in hydrochloric acid [843] and with hydrogen iodide and phosphorus [227], geiibrally in good to high yields. 

Uramil has been obtained by boiling alloxantin with ammonium chloride 1 by reduction of nitrosobarbituric acid or ryjtro-barbituric acid with hydrogen iodide 2 and by reduction of alloxan phenylhydrazone with tin and hydrochloric acid.3... 

The mechanism for the reaction is believed to be as shown in Eq. 15.170 (start with CH3OH, lower right, and end with CHjCOOH, lower left).180 The reaction can be initiated with any rhodium salt, e.g., RhCl3, and a source of iodine, the two combining with CO to produce the active catalyst, IRItfCO y. The methyl iodide arises from the reaction of methanol and hydrogen iodide. Note that the catalytic loop involves oxidative addition, insertion, and reductive elimination, with a net production of acetic acid from the insertion of carbon monoxide into methanol. The rhodium shuttles between the +1 and +3 oxidation states. The cataylst is so efficient that the reaction will proceed at atmospheric pressure, although in practice the system is... 

The valuable synthetic intermediates are benzo-2,l,3-selenadiazoles. They were used for preparation of. V-al ky I-1,2-benzenediamines, 3-nitro-1,2-benzenediamines, 3,4-diamino-2-nitrophenols, and 5-nitroqunoxalines. The key step of the reaction is their reductive deselenation with hydrogen iodide or, better, with ammonium hydrosulfide [233-238],... 

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