Main hurdles for synthesis Stereoselective introduction of

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Main hurdles for synthesis
Reason For Interest

• First discovered steroid with significant
  neurotrophic activity
• Has been seen to significantly induce neurite
  growth
• This is useful in the treatment of
  neurodegenerative diseases, such as Alzheimers,
  Parkinsons, and Huntingtons diseases.

• Stereoselective introduction of the side chain at
  C17 with the proper stereochemistry at C24
• Accommodation of the acetoxyl group on C16 in the
  context of the C3, C7, and C11 hydroxy groups
• Introduction of a 6-keto-7ß-hydroxy subunit
• Proper stereochemistry on the C11 hydroxy group.

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73
(7)
(6)
(a) AcCl, Ac2O, reflux, 17h (b) HC(OMe)3,
(CH2OH)2, p-TsOHH2O, CH2Cl2, reflux, 1.5h
(c)NaBH4, tBuOH-THF-H2O, 0C to room temperature,
48h, 73(three steps)
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3-5-dimethylpyrazole
5
38
Conditions NaBH4, CeCl37H2O, THF-MeOH, -70 to
-30 C, I h. 96
Luche Reduction Mechanism
http//www.organic-chemistry.org/namedreactions/lu
che-reduction.shtm
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(d) Ac2O, DMAP, pyridine, CH2Cl2, rt, 4 h, 98
(e) BH3-THF, THF, 0 C to room temperature, 12 h
NaOH, H2O2, 2 h, rt, 76
Xu, Shangjie Held , Ingmar Kempf, Bernhard
Mayr, Herbert Zipse, Hendrik The
DMAP-Catalyzed Acetylation of Alcohols - A
Mechanistic Study . Chem. Eur. J. 2005, 11, 4751
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(f) AcOH-H2O, rt, 2.5 h (g) 2,
2-dimethoxypropane, CSA, DMF, rt, 8 h (h)
EtPPh3Br, KOtBu, THF, reflux, 3 h, 67 (three
steps) (i) TBSOTf, 2,6-lutidine, CH2Cl2, rt, 1
h, 98
2, 2-dimethoxypropane
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(j)SeO2, t-BuOOH, CH2Cl2, 0C 5h, 72 (k)
Dess-Martin periodinane, CH2Cl2, 1h, 98
SeO2 allylic oxidation
Dess-Martin oxidation
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Synthesis of Vinyl Iodide
Conditions (a) Ac2O, Et3N, DMAP, CH2Cl2, rt, 12
h (b) O3,pyridine, CH2Cl2, -78 C then Me2S,
rt. 38 (two steps) (c) CrCl2,CHI3, THF, 0 C to
room temperature, 4 h, 45 (EZ ) 937).
Takai olefination
http//en.wikipedia.org/wiki/Takai_reaction
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(a) 29, t-BuLi, -78 C, Et2O, 0.5 h, then CuCN,
-40 C, 0.5 h 44, -70 C, 2 h, 61 (93 brsm)
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(b) LiAlH4, THF, -78C, 1 h (c) Ac2O, DMAP, Py.,
0 C, 4 h (d) (CH2SH)2, CSA, CHCl3, reflux, 1 h,
61 (three steps) (e) Dess-Martin periodinane,
CH2Cl2, rt, 3 h (f) HF-CH3CN-H2O, rt, 5 h, 61
(two steps).

• Overall yeild for the 20 step process is 3