Восстановление нитростиролов/пропенов хлоридом олова и алюминиевой амальгамой.

Эта реакция до сих пор почти что не опробована, главным образом потому, что существуют проверенные работающие методы, которые всех удовлетворяют. Однако же учитывая какие выходы обещает нам эта двухстадийная процедура при всей своей ОТСшности, трудно удержаться от соблазна её проверить...

Особенно учитывая, что она работает и на нитростиролах, и на нитроалкенах.

Сначала нитростирол восстанавливается в оксим гидратом хлорида олова (последний легко приготовить самому, растворив олово в соляной кте) в среде этилацетата или ацетона. Или же реакция проводится в щелочной среде - в этом случае вместо хлорида олова можно взять гидроксид (NB: щелочной метод работает только для нитропропенов)

Нужно отметить, что полученный оксим не обязательно восстанавливать в амин, а можно и гидролизовать в кетон (если речь идёт о восстановлении фенилнитропропенов), который стандартными методами переводится в амин (см. раздел Восстановительное аминирование.). Читайте эту процедуру здесь.

Затем полученный оксим восстанавливается любым из известных способов до амина. Наиболее простым способом является алюминиевая амальгама, возможно тж. каталитическое гидрирование и восстановление цинковой пылью в ледянке.

1. Восстановление в оксим:

а) В кислой среде:

The synthesis of 9-anthracenylacetaldoxime is representative of the procedure employed. 9-(omega-nitrovinyl)anthracene (1.25 gr, 5 mmol), SnCl2.2H2O (2.25 gr, 10 mmol) and ethyl acetate (25 mL) were placed in a 50 mL erlenmeyer flask and the mixture stirred at room temperature. A mildly exothermic reaction ensued which was accompanied by the gradual disappearance of the yellow coloration (nitroalkene). The reaction mixture was carefully poured into ice water and the solution was made slightly basic (pH 7--8) by addition of 5% aqeous sodium bicarbonate. The product was extracted into ether, washed with brine, dried (Na2SO4) and the solvent removed under reduced presure to yield essentially pure 9-anthracenylacetaldoxime, mp 177-80' (1.05 gr, 90%).

б) В щелочной среде.

The following procedure is representative: a sodium stannite solution was prepared by addition of aqeous sodium hydroxide (50 mmol, 2 gr in 15 ml of water) to aqeous stannous chloride (5 mmol, 1.12 gr in 15 ml water); the initially formed precipitate dissolved to form a clear solution. This solution was gradually added to the beta-nitrostyrene derivative (2 mmol, in 10 ml THF) at room temperature; a mildly exothermic reaction ensued. The reaction mixture was stirred for the specified time, saturated brine solution added, the product extracted into ether, (3x45 ml) and the worked up in the susual manner. Essentially pure product were obtained.

         R                  R

      CH=C-NO2          CH2-C=NOH

      |                 |

      .

     / \               /.\

     |O|          ->   |O|

     \./-R2            \./-R2

      |                 |

      R1                R1

    R    R1    R2      time (min)  Yield (as isolated, %)

    CH3  H     H       25           82

    CH3  Br    H       40           84

    CH3  OEt   OEt     90           71

2. Восстановление в амин.

а) Алюминиевой амальгамой.

JACS 111, 6228 (1989)

To a solution of the oxime (24.6 mg, 0.521 mmol) in 10% H2O-THF (30ml) were added aluminum amalgam, which was prepared from 0.25g of granular aluminum and 2% HgCl2 (0.1ml) in 10% H2O-THF (0.5ml). The reaction mixture was stirred for 3h at room temperature. 3ml conc NaHCO3 was added, and the reaction mixture was filtered and the filter cake washed with ethyl acetate. The filtrate was diluted with water and extracted with ethyl acetate. The extracts was washed with brine, dried over MgSO4 and concentrated in vacuo to give 20.34 mg (85%) of the desired amine as an oil. [Rh: The oxime they reduce here is a large indole derivative. Use less solvent with smaller molecules at a larger scale]

б) Алюминиевая амальгамой - процедура от AntiBody2

2,3-Dimethoxy,4,5-Methylenedioxy-Amphetamine-2,hydrogen chloride
7g of oxime was dissolved in 150mls dry THF and poured over activated 10g HD reynolds Al [9] followed by 18g GAA. It was allowed to react with mag stirring at RT overnight. In morning rxn was basifiied with 50% NaOH, and top THF layer was seperated, and stripped of solvent under low vac. The residue was dissolved in a portion of 2M HCl with much shaking. This was basiied and extracted with 150mls toluene, which was also stripped of solvent under low vac on a water bath. The residue being taken up in 50mls acetone, and gassed with dry HCl yeilding 3.75g of the title compound with a MP of 178-180C

3) Цинковой пылью.

JOC 57, 6324 (1992)

At room temperature with stirring, Zinc dust (74 mg) was added to a solution of the oxime (44mg, 0.185 mmol) in 2 ml glacial acetic acid. Stirring was continued for another 15 minutes. The reaction mixture was then filtered through a sintered glass funnel with suction. The filtrate was concentrated under vacuum to afford the amine as an oil (37mg, 0.166 mmol, 90% yield).

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