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"RANEY NICKEL HYDROGENOLYSIS OF THIOAMIDES: A NEW AMINE SYNTHESIS" E. Kornfeld  in J.O.C., 16, 131-138 (1951)



General procedure
The thioamide (10 g) was placed in a 500-ml. round-bottom flask with the wet catalyst, and 200 ml. of solvent (80% ethanol or 80% dioxane) was added. A slight exothermic reaction was often noted at this point. The mixture was then refluxed for the period noted in the Tables after which the flask was cooled. The catalyst was filtered and washed thoroughly with alcohol and a little water and dried to accurately determine the dry weight.
The filtrate was concentrated in vacuo, the crude product was taken up in ether, and dilute HCl was added to dissolve the amine. The acid axtract was separated, made alkaline with KOH, ether added, and the ether extract dried over solid KOH. Dry HCl was passed into the filtered ether solution, and the hydrochloride was purified by recristallization. In most instances alcohol-ether was a satisfactory solvent.

Hydrogenolysis of 3-Methoxyphenylthioacetomorpholide
------------------------------------------------------------
Grams Ni/Grams thioamide   Time, hours (solvent)    Yield,%
------------------------------------------------------------
5.2                          3.5 (E)                  52
5.6                          1.0 (E)                  64
2.6                          3.0 (E)                  68
3.1                          1.0 (E)                  69
1.6                          0.2 (E)                  46
1.6                          0.5 (D)                  44
2.6                          0.5 (I)                  50
------------------------------------------------------------
Solvents: E - 80% ethanol, D - 80% dioxane, I - 80% isopropanol

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А"Borohydride and Cyanoborohydride Reduction of Thioimonium Salts. A Convenient Route for Transformation of Amides to Amines" J.Org.Chem. 1981, 46, 3730-3732





.^a Reduction in the presence of ZnCl2. ^b Reduction in the presence of SnCl4.

General Procedure for Preparation of Thioamides.
To a solution of the amide (2.5 mmol) in dioxane (15 ml), which has been distilled from sodium benzophenone ketyl, was treated with P2S5 (3.0 mmol), and the heterogeneous mixture was stirred at r.t. for 2 h. The progress of the reaction was followed by TLC and, if necessary, the solution was warmed to 35⁰C until the amide was consumed. The dioxane was decanted from the residual solid and filtered. Evaporation of the dioxane left crude thioamide, which was purified by distillation or recrystallisation. Yields were 50-70%.

General Procedures for Methylation and Reduction of Thioamides.
The thioamide (1-5 mmol) was dissolved in anhydrous THF (10-25 ml) and treated with a fivefold axcess of methyl iodide. The reaction mixture was stirred at r.t. until disappearance of the thioamide was complete as judged by TLC (0.5-12 h). In most cases the salt precipitated. The THF was evaporated under reduced pressure and the residual salt dried in vacuo. The dry salt was then dissolved in dry methanol (25-50 ml) and treated cautiously with 1.1 molar equiv of solid sodium borohydride (vigorous gas evolution) or sodium cyanoborohydride. When sodium cyanoborohydride was to be used as the reducing agent, acetic acid (20 ml, 1:1 acetic acid/water) was added to the methanolic solution of the thioamide. Upon addition of the sodium borohydride there was immediate gas evolution, including methanethiol (stench). The reaction mixture was stirred for 2 h and then made strongly alkaline with 20% NaOH solution. The mixture was extracted with ether, and the extracts were dried over K2CO3, evaporated on a rotary evaporator, and distilled to give pure amines.


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