2444-102611

2444-102611 - Reactions 1 O H 2 , EtOH Pd-C H 2 , EtOH...

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Unformatted text preview: Reactions 1 O H 2 , EtOH Pd-C H 2 , EtOH Ni(R) H 2 , EtOH Pd-BaSO 4 H 2 , EtOH Pd-C H 2 , EtOH PtO 2 H 2 , EtOH quinoline E + Z or say E+Z OH N.R. Dissolving Metal Reductions: aldehydes and ketones 2 When sodium metal is mixed with a ketone in liquid ammonia and an alcohol, a reduction occurs to give an alcohol. In one typical experiment, 4- tert- butylcyclohexanone is treated with Na metal in liquid ammonia and tert-butanol to give 4- tert- butylcyclohexanol ( 59 ) in 98% yield . The only way an alcohol may be formed is via transfer of a hydrogen atom to both the carbon and the oxygen of the carbonyl unit. The only source of hydrogen, however, is either the ammonia (NH 3 ) or the alcohol ( t- BuOH). O O- H H 55 59 Na , NH 3 (-33C) Me 3 C Me 3 C Me 3 CO H Dissolving Metal Reductions: aldehydes and ketones 3 O O O O H O O- H H H 55 59 57 58 Me 3 C Me 3 C Me 3 C Me 3 C Me 3 C Me 3 C Na H OR RO H Na 56A 56B The mechanism involves transfer of a single electron from sodium metal to the carbonyl unit of the ketone to give a new type of intermediate , a radical-anion . In this case, the radical-anion is 56A and it is generically known as a ketyl . This ketyl is a resonance stabilized species and it can be drawn with the negative charge on either oxygen ( 56A ) or carbon ( 56B ), and the single electron (the radical) can be drawn on either oxygen or carbon. The resonance form that has the negative charge on carbon ( 56B ) functions as a carbanion Dissolving Metal Reductions: aldehydes and ketones 3 O O O O H O O- H H H 55 59 57 58 Me 3 C Me 3 C Me 3 C Me 3 C Me 3 C Me 3 C Na H OR RO H Na 56A 56B The mechanism involves transfer of a single electron from sodium metal to the carbonyl unit of the ketone to give a new type of intermediate , a radical-anion . In this case, the radical-anion is 56A and it is generically known as a ketyl . This ketyl is a resonance stabilized species and it can be drawn with the negative charge on either oxygen ( 56A ) or carbon ( 56B ), and the single electron (the radical) can be drawn on either oxygen or carbon. The resonance form that has the negative charge on carbon ( 56B ) functions as a carbanion base, and removes a proton from either ammonia or the alcohol in an acid-base reaction. Dissolving Metal Reductions: alkynes 4 Alkynes are reduced to alkenes in good yield using dissolving metal conditions, and the experimental evidence shows that the E- alkene is the major product. In a typical example, 4-octyne ( 60 ) is treated with sodium in liquid ammonia, and oct-4 E-ene ( 64 ) is isolated in 90% yield. None of the Z- alkene is observed in this reaction....
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This note was uploaded on 02/25/2012 for the course CHEM 244 taught by Professor Jardin,j during the Fall '08 term at UConn.

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2444-102611 - Reactions 1 O H 2 , EtOH Pd-C H 2 , EtOH...

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