Birch reduction



The Birch reduction is the hydrogenation, which usually reduces the aromatic ring all the way to a cyclohexane (after the initial reduction to a cyclohexadiene, catalytic reduction of the remaining (nonaromatic) double bonds is easier than the first reduction).

ethanol and tert-butanol can be used instead of ammonia.

Several reviews have been published.[3] [4] [5] [6]

Reaction mechanism

A solution of sodium in liquid ammonia consists of the radical anion followed by the dianion. These carbanions deprotonate the ammonia to form the cyclohexadiene.

Birch alkylation

In the presence of an alkyl halide the M-SG reducing agent, also exist.

In Birch alkylation the anion formed in the Birch reduction is trapped by a suitable haloalkane.[9] For example, in the reaction depicted below, 1,4-dibromobutane is added to t-butyl benzoate to form an alkylated 1,4-cyclohexadiene product.[10]:

References

  1. ^ (a) Birch, A. J. J. Chem. Soc. 1949, 2531.
  2. ^ Vogel, E.; Klug, W.; Breuer, A. (1974). "1,6-Methano-10-annulene". Organic Syntheses 54: 11.
  3. ^ Birch, A. J.; Smith, H. Quart. Rev. 1958, 12, 17. (Review)
  4. ^ Caine, D. Org. React. 1976, 23, 1-258. (Review)
  5. ^ Rabideau, P. W.; Marcinow, Z. Org. React. 1992, 42, 1-334. (Review)
  6. ^ Mander, L. N. Comp. Org. Syn. 1991, 8, 489-521. (Review)
  7. ^ Kuehne, M. E.; Lambert, B. F. (1963). "1,4-Dihydrobenzoic acid". Organic Syntheses 43: 22.
  8. ^ Paquette, L. A.; Barrett, J. H. (1969). "2,7-Dimethyloxepin". Organic Syntheses 49: 62.
  9. ^ Taber, D. F.; Gunn, B. P.; Ching Chiu, I. (1983). "Alkylation of the anion from Birch reduction of o-Anisic acid: 2-Heptyl-2-cyclohexenone". Organic Syntheses 61: 59.
  10. ^ Formation of Benzo-Fused Carbocycles by Formal Radical Cyclization onto an Aromatic Ring Derrick L. J. Clive and Rajesh Sunasee Org. Lett.; 2007; 9(14) pp 2677 - 2680; (Letter) doi:10.1021/ol070849l

See also
 
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