Reduction of conjugated arylalkenes and arylalkynes

In addition to the described reduction of double bonds conjugated to a carbonyl group, sodium hydrogen telluride and phenyltellurol reduce double (and triple) bonds conjugated to aromatic systems.  

PhTeH (PhTeli/TFA) method B PhTeH (PhTeSiMeg/MeOH) (method C) (ref. 4) 

High yields are obtained with terminal alkenes (styrene and a-methylstyrene) and with the strained acenaphthylene, whereas stilbene and -methylstyrene are barely reduced. 

Acenaphthene (typical procedure) Method A. To a solution of NaHTe (10 mmol, prepared as previously described) is added acenaphthylene (0.304 g, 2 mmol) in EtOAc (20 mL), and the mixture refluxed for 9 h. During this time a black Te precipitate is formed. After dilution with HgO (500 mL) the product is extracted with ether, the ethereal solution is dried (Na2S04) and evaporated and the residue chromatographed on SiOg, giving acenaphthene (0.303 g (99%)). 

Method B A mixture of diphenyl ditelluride (2.05 g, 5 mmol), NaBH4 (0.397 g, 10.5 mmol) and dry EtOH (20 mL) is heated with stirring under Ng atmosphere for 15 min, when most of the ditelluride had produced an almost colourless solution. The solution is then cooled to 20°C and TEA (0.81 g, 10.5 mmol) in EtOH (5 mL) is added, followed by a solution of acenaphthylene (0.305 g, 2 mmol) in EtOAc (20 mL). The mixture is refluxed for 4 h, then diluted with cold HgO (500 mL) and worked up in the usual manner, including SiOg chromatography, to give diphenyl ditelluride (1.93 g (94%)) and acenaphthene (0.300 g (98%)). 

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