01-31-01 17:57
No 170334
      Novel reductive amination with PMHS-Ti(OiPr)4
(Rated as: excellent)

A single step reductive amination of carbonyl compounds with polymethylhydrosiloxane-Ti(OiPr)4
S. Chandrasekhar, Ch. Raji Reddy, Moinuddin Ahmed
Synlett 11, 1655 (2000) (../rhodium/pdf /redamin.pmhs.ti-isopropoxide.pdf)

Highly chemoselective ‘one pot’ amination of carbonyl groups is achieved using polymethylhydrosiloxane (PMHS) as reductant and Ti(OiPr)4 as activator. A comparative study with other activators such as AlCl3 and Pd-C was also studied.

General Experimental Procedure
A mixture of carbonyl compound (1 mmol), amine (1 mmol) and titanium(IV)isopropoxide (0.355mg, 1.25 mmol) was stirred at room temperature. After 1 hour, PMHS (120mg, 2 mmol) dissolved in THF(5 mL) was added and the solution was stirred (Table 2). The reaction mixture was cooled and sodium hydroxide solution (3 N, 10 mL) was carefully added dropwise (at first there is vigorous gas evolution). After stirring for 20 minutes, the solution was extracted with ether (3x20 ml). The combined ether layers were washed with brine, dried (Na2SO4) and evaporated in vacuo to give the amine in essentially pure form.

Yields for different carbonyls (benzaldehyde, p-nitro-benzaldehyde, cinnamaldehyde, acetophenone, benzophenone, 2-methyl-cyclohexanone, camphor) and amines (benzylamine, aniline, piperidine) are good (83-92%). smile