Chromous acetate reduction with

Divalent chromium salts show very strong reducing properties. They are prepared by reduction of chromium(III) compounds with zinc [187] or a zinc-copper couple and form dark blue solutions extremely sensitive to air. Most frequently used salts are chromous chloride [7SS], chromous sulfate [189], and less often chromous acetate. Reductions of organic compounds are carried out in homogeneous solutions in aqueous methanol [190], acetone [191], acetic acid [192], dimethylformamide [193] or tetrahydrofuran [194] (Procedure 37, p. 214). 

Isophorone usually contains 2—5% of the isomer P-isophorone [471-01-2] (3,5,5-trimethyl-3-cyclohexen-l-one). The term a-isophorone is sometimes used ia referring to the a,P-unsaturated ketone, whereas P-isophorone connotes the unconjugated derivative. P-lsophorone (bp 186°C) is lower boiling than isophorone and can be converted to isophorone by distilling at reduced pressure ia the presence of -toluenesulfonic acid (188). Isophorone can be converted to P-isophorone by treatment with adipic acid (189) or H on(Ill) acetylacetoate (190). P-lsophorone can also be prepared from 4-bromoisophorone by reduction with chromous acetate (191). P-lsophorone can be used as an iatermediate ia the synthesis of carotenoids (192). 

A new synthesis of substituted 1,3-dienes by reductive elimination of allylic nitro derivatives has been reported (Eq. 7.134).180 Tertiary allylic nitro compounds, bearing an acetate group in the (3-position, smoothly undergo reductive elimination to give conjugated 1,3-dienes when treated with chromous acetate and 2,2-dipyridine in DMF at 111-120 °C. 

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. 

The partial synthesis from solasodine of nitrogen-containing analogues of ecdysone has been explored.22 In the successful route, 7V,0-diacetylsolasodine (16b) was treated with TV-bromo acetamide and HCI04. The bromohydrin (26a) that was formed was reductively debrominated with chromous acetate and butanethiol to... 

Reduction of at,p-oxidoketones. In a study of potential routes to the A/B ring system of cardiac-active steroids (periplogenin, strophanthidin), Robinson and Henderson studied the reduction of 4/ ,5/ -oxidocholestane-3-onc (1) with chromous acetate. The best results were obtained by reduction of (I) with a large excess of freshly... 

Reduction of an a-bromoketone. 2a,4o -Dibromocholestane-3-one was reduced to 4a-bromocholestane-3-one in 78% yield with freshly prepared chromous acetate taken in large excess. With the theoretical amount of reagent the yield was only 20%/... 

Reduction of bromohydrlns. Barton and Basu° found that reduction of a 9a-bromo-11/3-hydroxy steroid with a large excess of chromous acetate in the presence of butanethiol as hydrogen donor gives the 11/3-hydroxysteroid in high yield. The... 

Chromous chloride was used to effect reductive eleavage of the y-lactone (5). In this case reduction with zinc and acetic acid or with calcium and liquid ammonia proceeded very slowly. 

Reductive dehalogenation [1, 149, before references]. Reduction of 1.2,3,4,7,7-hexachloro-5-ent/o-acetoxybicyclo[2.2. l]-2-heptcnc (1) with chromous acetate... 

Reduction of enediones. A4-Cholestene-3,6-dione (1) is reduced by chromous chloride in either THF or acetone to 5/3-cholestanone-3,6-dione (2).3 Note that reduction with zinc and acetic acid gives the more stable 5a-cholestane-3,6-... 

Conversion of ketoximes into ketones. Corey and Richman1 have reported a new procedure for regeneration of ketones from their oximes. The oxime is first converted into the O-acetate by treatment with acetic anhydride at 20° this derivative is then reductively deoximated by treatment with > 2 molar equivalents of chromous acetate in 9 1 THF-water at 25-65°. The reaction presumably involves reductive fission of the oxime N—O linkage to give an imine which is then rapidly hydrolyzed. Yields are in the range 75-85%. It is noteworthy that the reaction occurs more readily with acetoximes of conjugated ketones than with those of nonconjugated ketones and that the reaction occurs readily with acetoximes of hindered ketones such as camphor. 

The reaction also has been used for transposition of a carbonyl group. Oxidation of propiophenone (4), followed by reduction with sodium borohydride and acetylation, gives the a-acetoxy acetoxime (5), which on treatment with excess chromous acetate affords phenylacetone (6). 

Cobalt(II) complexes (such as cob(II)alamin, formerly called B,2,) can be obtained by several methods including controlled potential reduction [14,15], anaerobic photolysis of some organocobalt species [16] (see Section 5.2(b)), partial oxidation of cobalt(I) complexes, in some cases acidification of solutions of cobalt(I) complexes (see below) and chemical reduction. Chemical reduction of cobalt(III) cobalamins to the +2 oxidation state has been achieved with hydrogen over platinum oxide [16], with neutral and acidic solutions of vanadium(III) [17], with chromous acetate at pH 3 [18] and with amalgamated zinc in 0.1 M aqueous perchloric acid [19]. All such cobalt(II) species are probably 5-coordinate, and are low spin d systems containing an unpaired electron and thus displaying an ESR spectrum [20]. 

Reduction of (1) with chromous acetate in the presence of acetic anhydride gives the normal enamide with no epimerization of the 13-methyl group. 

Also obtained from dehydrogriseofulvin by reductive scission with chromous chloride or with zinc in acetic acid [1192],... 

The purity of RDX may be detd by the Chromous Chloride Method of Jamison (Ref 3)- This method consists in the reduction of RDX in an acetic-HC1 soln with chromous chloride and back-titra-... 

Alkenes are converted to epoxides by oxidation with peroxy acids, and thereby they are protected with regard to certain chemical transformations. Alkaline hydrogen peroxide selectively attacks enone double bonds in the presence of other alkenes. The epoxides can be transformed back to alkenes by reduction-dehydration sequences or using triphenylphosphine, chromous salts, zinc, or sodium iodide and acetic acid. A more advantageous and fairly general method consists, however, of the treatment of epoxides with dimethyl diazomalonate in the presence of catalytic amounts of binuclear rhodium(II) car-boxylate salts. This deoxygenation proceeds under neutral conditions and without isomerization or cy-clopropanation of the liberated alkene (Scheme 97). Furthermore, epoxides can be converted to alkenes with the aid of various metal carbonyl complexes. Thus, they may be nucleophilically opened with... 

Reductive cleavage of 2,4-dinitrophenylhydrazones. Certain 2,4-dinitrophenyl> hydrazones of 3-ketosteroids can be cleaved under mild conditions if the nitro groups are reduced to amino groups by chromous chloride. Thus when the 2,4-DNP of 4,5a-dihydrocortisone 21-acetate in methylene chloride was shaken in a separatory funnel with chromous chloride and dilute hydrochloric acid for 15 min., workup of the organic layer afforded the ketone in 94% yield. Use of a water-immiscible solvent protects the released ketone an inert atmosphere if required can be provided with dry ice. Cortisone 2,4-DNP was cleaved in only 3-5 hrs. and the yield was 60%. DN P derivatives of A -diene-S-ones were completely resistant to hydrolysis. Contributed by Leon Mandell... 

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