Carbonyl reduction

Carbonyl reduction
synthesis of an alcohol by ester reduction

Carbonyl reduction in organic chemistry is the organic reduction of any carbonyl group containing compound by a reducing agent. Typical carbonyl compounds are ketones , aldehydes, carboxylic acids and esters. A carbonyl group can be reduced to the alcohol or the oxygen atom can be removed altogether, a process called deoxygenation. Many reducing agents are metal hydrides based on boron and aluminum. A second important method is catalytic hydrogenation. [1] [2].

Contents

Metal hydride mechanism

The reaction mechanism for metal hydride reduction is based on activation of the carbonyl group by the metal followed by nucleophilic addition of hydride. Another general system is catalytic hydrogenation by metal. LiAlH4 is more reactive than NaAlH4 because the smaller lithium cation is a better Lewis acid. A crown ether reduces reactivity. Alkoxide substitution in metal hydrides increases solubility and selectivity. An example is Red-Al.

Aldehyde and ketone reduction

The reaction product of the reduction of an aldehyde is a primary alcohol and that of a ketone a secondary alcohol. Reagents are lithium aluminium hydride [3] [4] [5], diisobutylaluminium hydride, sodium borohydride, L-selectride, diborane, diazene and aluminum hydride. Sodium borohydride tolerates more functional groups (nitro group, nitrile, ester) than LiAlH4 and can also be used with water or ethanol as a solvent (LiAlH4 reacts with protic solvents). Sodium cyanoborohydride, 9-BBN-pyridine and tributyltin hydride are selective for aldehydes. A method for selective ketone reduction in presence of an aldehyde is NaBH4 / cerium chloride.

In hydrogenation platinum and ruthenium are preferred catalysts. Specific methods are the Meerwein–Ponndorf–Verley reduction (aluminumisopropylate/isopropanol), the Bouveault–Blanc reduction (sodium metal/ethanol) and the Cannizzaro reaction (KOH induced aldehyde disproportionation)

Carboxylic acid reduction

Typical reagents for the reduction of carboxylic acids or carboxylate salts to alcohols are lithium aluminium hydride , diborane, DIBAL and aluminum hydride. Catalytic hydrogenation and NaBH4 are ineffective.

Ester reduction

Esters (R(CO)OR') can be reduced to alcohols RCH2OH and R'OH by lithium aluminium hydride [6] [7] and aluminum hydride. Diisobutylaluminium hydride and lithium tri-t-butoxyaluminum hydride are selective for the formation of the aldehyde. Catalytic hydrogenation over copper chromite is reported.

1,4-reduction

In 1,4-reduction (also called conjugate reduction) the reaction substrate is an unsaturated carbonyl compound, an enone or enal. The 1,2-reduction product (an allyl alcohol) competes with 1,4-reduction to the saturated ketone or aldehyde. In 1,4-reduction the first step is conjugate addition of the hydride to the enolate ion followed by acidic workup forming the ketone.

1,2-reduction is found with DIBAL and 9-BBN and alane. 1,4-reduction can be accomplished with catalytic hydrogenation and by alkylmetal hydrides.

An example is the reduction of chalcone by tributyltin hydride [8]:

Conjugate reduction chalcone
Conjugate reduction chalcone

An asymmetric version of this reaction has also been developed [9].

Asymmetric synthesis

Well known carbonyl reductions in asymmetric synthesis are the Noyori asymmetric hydrogenation (beta-ketoester reduction /Ru/BINAP) and the CBS reduction (BH3, proline derived chiral catalyst).

References

  1. ^ Advanced organic chemistry: Structure and mechanisms Francis A. Carey, Richard J. Sundberg 2nd Ed.
  2. ^ March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (3rd ed.), New York: Wiley, ISBN 0-471-85472-7 
  3. ^ Organic Syntheses, Coll. Vol. 7, p.129 (1990); Vol. 60, p.25 (1981). Link
  4. ^ Organic Syntheses, Coll. Vol. 6, p.887 (1988); Vol. 58, p.12 (1978). Link
  5. ^ Organic Syntheses, Coll. Vol. 6, p.769 (1988); Vol. 56, p.101 (1977). Link
  6. ^ Organic Syntheses, Coll. Vol. 6, p.781 (1988); Vol. 53, p.70 (1973). Link
  7. ^ Organic Syntheses, Coll. Vol. 4, p.834 (1963); Vol. 33, p.82 (1953). link
  8. ^ Leusink, A.J.; Noltes, J.G. (1966). "Reaction of organotin hydrides with α,β-unsaturated ketones". Tetrahedron Letters 7 (20): 2221. doi:10.1016/S0040-4039(00)72405-1. 
  9. ^ Moritani, Yasunori; Appella, Daniel H.; Jurkauskas, Valdas; Buchwald, Stephen L. (2000). "Synthesis of β-Alkyl Cyclopentanones in High Enantiomeric Excess via Copper-Catalyzed Asymmetric Conjugate Reduction". Journal of the American Chemical Society 122 (28): 6797. doi:10.1021/ja0009525. 

Wikimedia Foundation. 2010.

Нужно сделать НИР?

Look at other dictionaries:

  • Carbonyl — In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double bonded to an oxygen atom : C=O. The term carbonyl can also refer to carbon monoxide as a ligand in an inorganic or organometallic complex (a metal… …   Wikipedia

  • Meerwein–Ponndorf–Verley reduction — The Meerwein Ponndorf Verley (MPV) Reduction in organic chemistry is the reduction of ketones and aldehydes to their corresponding alcohols utilizing aluminumalkoxide catalysis in the presence of a sacrificial alcohol[1]. The beauty in the MPV… …   Wikipedia

  • Meerwein-Ponndorf-Verley reduction — The Meerwein Ponndorf Verley Reduction in organic chemistry is the reduction of ketones to secondary alcohols with aluminumisopropylate catalysis in isopropanol solution [Alexander R. Surrey, Name Reactions in Organic Chemistry, 2nd Edition,… …   Wikipedia

  • Vanadium carbonyl — Chembox new Name = Vanadium carbonyl ImageFile = V(CO)6.png ImageSize = 200px ImageName = Vanadium carbonyl IUPACName = hexacarbonylvanadium(0) OtherNames = vanadium carbonyl Section1 = Chembox Identifiers CASNo = 20644 87 5 RTECS = Section2 =… …   Wikipedia

  • Nickel carbonyl — Chembox new Name = Nickel carbonyl ImageFile = Nickel carbonyl 2D.png ImageSize = 150px ImageName = Nickel carbonyl ImageFile1 = Nickel carbonyl 3D vdW.png ImageSize1 = 150px ImageName1 = Nickel carbonyl IUPACName = Tetracarbonylnickel(0)… …   Wikipedia

  • Thiophene-2-carbonyl-CoA monooxygenase — In enzymology, a thiophene 2 carbonyl CoA monooxygenase (EC number|1.14.99.35) is an enzyme that catalyzes the chemical reaction:thiophene 2 carbonyl CoA + AH2 + O2 ightleftharpoons 5 hydroxythiophene 2 carbonyl CoA + A + H2OThe three substrates… …   Wikipedia

  • Luche reduction — is the selective organic reduction of ketones to alcohols with lanthanoid chlorides such as cerium(III) chloride and sodium borohydride as enones or in presence of aldehydes [Strategic Applications of Named Reactions in Organic Synthesis… …   Wikipedia

  • Corey-Itsuno reduction — The Corey Itsuno Reduction, also known as the Corey Bakshi Shibata (CBS) reduction, is a chemical reaction in which an achiral ketone is enantioselectively reduced to produce the corresponding chiral, non racemic alcohol. The oxazaborolidine… …   Wikipedia

  • Clemmensen reduction — is a chemical reaction described as a reduction of ketones (or aldehydes) to alkanes using zinc amalgam and hydrochloric acid.[1][2][3] This reaction is named after Erik Christian Clemmensen, a Danish chemist.[4] …   Wikipedia

  • One-electron reduction — A one electron reduction in organic chemistry involves the transfer of an electron from a metal to an organic substrate. It serves to differentiate between true organic reductions and other reductions such as hydride transfer reactions that… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”