Exam Red.

Question 1

LAH (lithium aluminiumhydride)

Answer 1

Powerful, non selective, moisture sensitive
Work up Rochelle’s salt or can use EA.
-78 oC, ether or THF
Imine, amide -> amine
Acid halide, aldehyde, ester, carboxylate -> alcohol

Question 2

LiBH4

Answer 2

Ester, lactone -> alcohol
Carboxylate ->X
0 oC, Ether > TFH > 2-propanol
Store protected from moisture

Question 3

BH3.L

Answer 3

COOH -> -CH2OH
Ester, lactone, amide, halide -> X
Aldehyde, ketone, alkene -> OH
In THF or Me2S
0-25 oC
Generate diborane in situ by using NaBH4/BF3.Et2O

Question 4

DIBAL

Answer 4

Ester -> CHO
Lactone -> lactol
Nitrile -> CHO
-78 oC, ether, or Toluene or DCM
Weinreb amide to aldehyde.****

Question 5

LTEAH (Lithium triethoxyaluminumhydride)

Answer 5

Amide ->Aldehyde
LAH + 3 EtOH -> LTEAH + 3H2
1. Ether, THF, hexane
2. H+

Question 6

Acid chloride -> Aldehyde

Answer 6

• Rosemund: from COOH
  1. SOCl2
  2. H2, Pd/BaSO4
• STBA (Sodium tri-tert-butoxyaluminiumhydride)
  STBA, diglyme, THF, -78 oC

Question 7

Aldehyde, ketone -> alkane

Answer 7

• Deoxygenation of Tosylhydrazone
  1. TsNHNH2, EtOH
  2. 90 oC, Na(CN)BH3, MeOH (may need acid, ZnCl2)
  2. Wolff-Kishner Red.
  2.1. diethylene glycol, Na, H2NNH2, 210 oC
  2.2. TBSH (N-tert-butyldimethylsilylhydrazone), Sc(OTf)3; t-BuOK, t-BuOH, DMSO, 23-100 oC, 24h.
  3. Thioacetal (thioketal) react with (Raney Ni, H2)
  4. Clemmensen Red.
  40% aqueous HCl, Zn(Hg)

Question 8

NaBH4

Answer 8

Aldehyde, ketone -> alcohol
At 25oC, ester, epoxide, lactone, carboxylate, nitro, nitrile -> X
25 oC, EtOH or MeOH.

Question 9

Luche reduction

Answer 9

NaBH4, CeCl3 allylic alcohol

MeCN, or MeOH

Question 10

Ionic halogenation ***

Answer 10

Proton donor combination with hydride donor
Organisilane + TFA
Reduction of carbonium ion generated by protonation of ketone, alkene, or a lactol.

Question 11

Samarium iodide (SmI2)

Answer 11

Aldehyde, ketone -> alcohol
Alkyl halide -> ????
Carboxylate, ester -> X
SmI2, THF/ H2O or iPrOH.
Meerwein-Ponndorf-Verley red.

Question 12

Reductive amination

Answer 12

C=O + Anime (mild acid) then Na(CN)BH3, Sn(OTf)3
4 A MS, DCE, 0 oC.
Or MeOH

Question 13

Barton Deoxygenation **

Answer 13

R-OH -> thiocarbonate -> RH

1. 1,1’-thiocarbonyl-imidazole, DMAP, DCM
2. AIBN, Bu3SnH, toluene, 75 oC

In Tin-free Barton-type reduction
B(CH3)3, H2O\Benzene, 23 oC

Question 14

Diazene-Mediated deoxygenation ????

Answer 14

R-OH->R-N(NH2)SO2Ar->RH
1. PPh3, DEAD, NBSH (Mitsunobu displacement)
THF, -30 oC
NBSH (o-nitrobenzenesulfonylhydrazine)
DEAD (Diethyl azodicarboxylate)

** Add alkyllithium to N-t-butyldimethylsilyl aldehyde tosylate hydrazine at -78 oC followed by acid.????

Question 15

Reduction of alkyl tosylate

Answer 15

LAH is not very good.
use LiEt3BH (super hydride) give higher yield!
toluene, 90 oC
or THF, H2O2, NaOH, MeOH

Question 16

Radical dehalogenation

Answer 16

Reduction of Chloride need hard condition
when Fluoride is not work in pratice.
Formed radical 3o > 2o > 1o (stability)
Bu3SnH, AIBN, THF, PhBr 80 oC
AIBN (azobisisobutyronitrile) –> 2-cyanoprop-2-yl radical when heat or hv

Question 17

Barton decarboxylation

Answer 17

R-COOH -> RCOCl
RCOCl + N-hydroxypyridine-2-thione -> Barton ester
–> Then radical (t-BuSH, toluene, 80 oC/// or Bu3SnH)

Question 18

Diol -> Olefin

Answer 18

Corey-Winter Olefination
Diol + thiocarbonyldiimidazole -> thiocarbonate
Can use alternative approach:
1) diol + Cl2C=S, DMAP
2) decomposition P agent

Eastwood Deoxygenation
Diol + HC(OEt)3, AcOH -> ortho ester heat –> Decompose

Decompose bezilidene acetal
LDA, t-BuOK, THF, heat.

Stryker reduction