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Org. Syn. > Oxidation > Flashcards

Oxidation Flashcards

1
Q

@Ox: Side reaction generate MTM from DMSO (Pummerer Rearangement)

A

R-OH attack to (CH2=S-CH3)+ generate from the dissociation of sulfoium ylide intermediate.

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2
Q

@Oppenauer Ox is related to

A

Meerwein-Pondorff-Verley Reduction (Acetone, Metal alkoxide)

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3
Q

How to activate MnO2?

A

By adding activated carbon.

C could be activated by make fine powder and high heat.

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4
Q

What is oxone

A

2KHSO5.KHSO4.K2SO4

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5
Q

TIPS, TBS

A

Triisopropylsilyl, t-butyldimetylsilyl

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6
Q

Wt’ll include in this course?

A

+ Oxidation
+ Protecting group
+ Name reaction
+ Reagent

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7
Q

Some info about DMSO:

A

High bp, could be seperated by NaCl sarturated
Need activation to form sulfonium ylide, side product MTM (CH3 2-3 ppm)
Can dissolve inorganic coumpounds
Activator 3eq, overnight, rt., 30-40eq DMSO
Me2S volatile; not good for multi gram scale

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8
Q

Name as many oxidation method as you can:

from alcohol to aldehyde or ketone

A
  1. Dimethylsulfoxide-mediated Ox
  2. Dess-Martin Periodinane (DMP)
  3. o-iodoxybenzoic acid (IBX)
  4. tetra-n-propylamonium perruthenate (TPAP)
  5. N-oxoamonium-mediated ox.
  6. Manganese dioxide
  7. Barium Manganate
  8. Oppenauer Ox
  9. Chromium (VI) oxidants
  10. Sodium hypochlorite
  11. N-bromosuccinimide (NBS)
  12. Bromine
  13. Cerium (IV) oxidants
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9
Q

DMSO-mediated ox include

A
  1. Swern Ox. (Oxalyl chloride) ~ -70 oC
  2. Pfitzner-Moffatt Procedure (DCC, EDC) ~
  3. Parikh-Doering Pro. (SO3.py) ~ -15 -> 23 oC
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10
Q

DMP

A

Short time reaction, single eq. of oxidant
IBX (o-iodoxybenzoic acid, heat and shock sensitive) is DMP’s precursor
H2O accelerate the reaction

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11
Q

Deprotection of PMB or MPM (Bn) by

A

DDQ (dichlorodicianoquinone)

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12
Q

IBX (o-iodoxybenzoic acid)

A

is a mild reagent for ox. of 1,2-diol
Prepare by o-iodobenzoic acid + oxone at 70 oC
2-6 eq IBX + DMSO form a,B-unsatuated carbonyl compound from corresponding alcohol or carbonyl compound.

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13
Q

TPAP (tetra n-propylamonium Perruthenate Pr4N+RuO4-)

A

mild and selective ox in various solvent.
in conjunction with stoichiometric ox. NMO (N-methylmorpholine-N-oxide) will create non-toxic, room temperature operating oxidant

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14
Q

TEMPO (2,2,6,6-tetramethylpiperidinyloxyl)

A

unstable but cannot buy.–> in situ
Mild and selective and stoichiometric oxidant
Use with various other stoichiometric oxidants:
m-CPBA; NaOCl (sodium hypochlorite);
BAIB [bis(acetoxy)-iodo]benzene
sodium bromite (NaBrO2)
Oxone (2KHSO5.KHSO4.K2SO4)

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15
Q

MnO2

A 
Must be used in active form
Could be deactivate by polar solvent
50-100 eq
Can oxidate syn or anti vivinal diols
Vinyl stannanes are not tolerate
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16
Q

BaMnO4 (Barium manganate)

A

allylic and benzylic alcohol only

17
Q

Tertiary allylic alcohols could be oxidize by

A

Cromium (VI) oxidants

18
Q

Collins reagent
//
Corey’s reagent

A

CrO3.py2 (hydroscopic, 6 eq in chlorinated solvent). Prepare by adding CrO3 to pyridine.!!!!
//
PCC (air stable, not very hydroscopic, 1.5 eq in DMF or DCE or a suspension with chlorinated solvents)
molecular seives can accelerate the rate of reaaction.

19
Q

NaOCl (sodium hypochlorite)

A

oxidize 2o alcohol in the present of 1o ones.
Use with AcOH.
Could replace by Calcium hypochlorite (a stable, easy to handle solid hypochlorite oxidant.

20
Q

NBS
//
bromine

A

Ox II alcohol in the presence of I alcohols. (Create Br+, -OH more Nu will react.
//
Br/AcOH can only oxidize activated alcohol (like lactol)

21
Q

cbz is PG of?

How to deprotect?

A

Amine with at least 1 N-H

H2 (Pd/C)

22
Q

Sodium chlorite (NaClO2)

A

A mild, inexpensive and selective reagent -CHO –> -COOH. Offen used with scavenger (2-methyl-2-butene, NaH2PO4, t-BuOH and H2O)

23
Q

Dithiol protect aldehyde is a good PG it is stable in most of condition but could be easy to deprotect by

A

PIFA (CF3CO2)IPh, ACN, H2O at 0 oC
Phenyliodine (III) bis(trifloroacetate)
The PG if used < 8C –> Terrible smell!!!

24
Q

Diazomethene (CH2N2)

A

N2 is one of the best LG in Org. Syn.
Methylation of -COOH
By-product could be easily removed because everything this volatile!!! How great!!!

25
Q

Oxidation could be in acid or base but if in the molecule have a lot of oxigen atoms which will prefer?

A

Base!

KMnO4 could be use in a wild range of pH but for this kind of molecule we usually cooperate it with NaH2PO4

26
Q

Ag2O, NaOH

A

A classic method for -CHO –> -COOH

For unsaturated system the highly basic condition could lead to some problem!

27
Q

Pyridinium dichromate (pyrH+)2CrO7 – PDC

A

PDC is stable prepare by dissolve CrO3 in a small amout of H2O. After that add Py. and collect precipitated product
Ox. non-conjugated aldehyde and primary alcohol.

28
Q

-CHO + (PDC/DMF, 6eq MeOH) –>

A

-COOMe
Reaction is less successful with EtOH or PrOH
Excellent if don’t want to use CH2N2
//
Could use AcCl to create HCl in situ to activate estirification reaction.

29
Q

Corey Gilman Ganem Ox.

A

Convert unsaturated aldehyde to methyl ester.
MnO2, NaCN/ AcOH, CH3OH
Becareful with NaCN as it could be converted into HCN in acidic condition.
1. NaCN, AcOH, CH3OH, 1h
2. MnO2

30
Q

-CHO –> COOR with bromine

A 
Br2, H2O, alcohol, NaHCO3
Oxidant Br+, need base.
Secondary alcohol is not affected
Oxidation of hemiacetal is proposed.
A variety of ester can be prepared!
Benzylidene acetals and thioketals are incompatible
31
Q

Bayer-Villiger Oxidation

A

Reagent (mCPBA, t-BuOOH,…)

Ketone to ester (insert O to the bond between C (carbonyl) and more steric Carbon.

32
Q

Alcohol to acid

A
  • RuO4
    Offen use Ru3+ or Ru4+ and a schochiometric oxidant NaIO4, NaOCl
    Add ACN could /^ catalyst turnover (avoid formation of insoluble Ru-carboxylate)
  • Molecular Oxygen
    O2/Pt
    II -OH do not oxidize!
33
Q

Jones oxidation

A

H2CrO4 in H2SO4
Acetone is solvent (will reaction with excess reagent)
Could lead to polimerization of olefins
1,2-diols and a-hydroxy ketones are susceptible to cleavage under this condition.

34
Q

PDC (pyridinium Dichromate)

*****

A 
Corey-Schmidt Ox.
Or Cornforth's reagent
In DMF ox. Alcohol to acid
in DCM ox. alcohol to aldehyde
In DMF, MeOH (excess) -> Methyl ester

Org. Syn. (5 decks)

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