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Chemistry 2 > Chemistry Y5: Organic synthesis > Flashcards

Chemistry Y5: Organic synthesis Flashcards

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1
Q

Where do curly arrows start from?

A

A lone pair/ bond that will break/ negative charge

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2
Q

If a curly arrow leads to 5 pairs on an atom what must you do?

A

Add another curly arrow to break one of the bonds

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3
Q

Rank the reactivity of these carbonyl groups:
Aldehyde, Ester, acid chloride, Ketone, amide, anhydride

A
  1. A C
  2. Anhydride
  3. Aldehyde
  4. Ketone
  5. Ester
  6. Amide
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4
Q

Is a carbonyl more reactive if it is electron withdrawing or electron donating?

A

More electron withdrawing

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5
Q

What are the 4 ways to react carbonyls?

A
  1. Nucleophilic addition
  2. Nucleophilic addition/ elimination
  3. Nucleophilic addition/ elimination/Nucleophilic addition
  4. Interconverting carbonyl groups having different OX states
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6
Q

What is an example of Nu addition of carbonyls

A

Aldehyde to secondary Alcohol

*Me-MgBr then quench

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7
Q

What is an example of Nu Addition- Elimination in carbonyls

A

Acid chloride to Amide

*R-NH2 (LP on N attack C)
-RNH3
*R-NH2 attacks again (LP attacks H)
-Cl

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8
Q

In the Nu Addition-Elimination of Acid chloride to amide what is happening to the electropholicity (reactivity)

A

It is decreasing

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9
Q

What is essential for the Nu Addition - elimination reactions of carbonyls

A

A good LG

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10
Q

What is a reaction scheme for Nucleophilic addition/ elimination/ addition of an ester?

A

Ester -(ADD)- (ELIM)->
Aldehyde -(QUENCH/ ADD) -> primary alcohol

H3Al+-H- is the Nu
2 lots of H- attack

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11
Q

How do you get from an Aldehyde to a carboxylic acid?

A

CrO3, H+ (Jones reagent)

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12
Q

How do you get from a carboxylic acid to an Ester

A
  1. MeOH
  2. Cat. H+
    -H2O = LG
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13
Q

How do you get from a primary alcohol carboxylic acid

A

CrO3. H+ (Jones Oxidation)

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14
Q

How do you get from an Ester to a primary alcohol

A
  1. LiAlH4
  2. H2O
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15
Q

How do you get from a primary alcohol to a Ketone

A

PCC, Cl-CrO3⁻
* Ketone is quite reactive so LiAlH4 isn’t needed

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16
Q

How do you get from an Aldehyde to a primary alcohol

A

LiAlH4
or
NaBH

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17
Q

How do you get from a secondary alcohol to a ketone?

A

CrO3 + ACID (H+, H2SO4, HCl)

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18
Q

How do you make acid chloride from carboxylic acid?

A

C. acid —(SOCl2) –> Acid Chloride

:O(H) of C. Acid attacks S of SOCl2
:B attacks H (making e.g. HCl)
Products = Cl- , SO2 (g) bubbles off, AC

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19
Q

What are organometallics and what are they used for?

A

They’re Nu’s, and strong bases (Lewis Base)
They are good for C-C bonding
R- M+ (ionic)
The more E+ve the metal the more reactive the Nu

CH3-Li
CH3-MgBr

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20
Q

How do you make R-MgBr? What are the conditions?

A

R-Br + Mg (s) —(Et2O DRY) –> R-MgBr

*Solvent must be DRY as OrganoMg reacts with water -> ACID
*Mg should get reduced in this reaction (shd get warm)

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21
Q

why is Et2O a v good solvent?

A

It has 2 LPs

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22
Q

What are Alkynyl Grignard reagents?

A

R - = - MgBr

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23
Q

How do you make Alkynyl Grignard reagents?

A

R - = - H + H3C-MgBr ->
R - = ⁻ + MgBr⁺ + CH4. <—> R - = - MgBr

H3C-MgBr is a waste product so should be used sparingly

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24
Q

What are the possible reactions with organomagnesium?

A
  1. Nu addition
  2. Nu addition/ elimination/ addition
  3. Nu addition/eliminaiton
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25
Q

Nu Addition with organoMg

A
  1. Formaldehyde -> 1. Alcohol
  2. Aldehyde -> 2. Alcohol
  3. Ketone -> 3. Alcohol

Reagents:
1. R’‘MgBr
2. H2O

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26
Q

Nu Addition/elimination/ addition with organoMg

A

Ester -> Ketone -> 3. Alcohol

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27
Q

Nu addition/ elimination with organo Mg

A

Acid chloride -> Ketone (1eq)
AC -> ketone -> 3. Alcohol (2eq)

(eqs of R’‘MgBr)

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28
Q

How do you make organoLi

A

R-Br + 2Li —(EtO2 DRY)–> R-Li, Li-Br

R⁻Li⁺

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29
Q

If you want to make a ketone using organoMg what should you start with?

A

Acid chloride and 1eq of R’‘MgBr

Not Ester as you will get a mixture of Ketone, 3. Alcohol and ester

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30
Q

What is the structure of Et2O

A

H3C-C(H2)-O-C(H2)-CH3

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31
Q

What are the 3 types of selectivity?

A
  1. Regioselectivity
  2. Stereoselectivity
  3. Chemoselectivity
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32
Q

What is stereochemistry?

A

The biological and physical properties of organic molecules depend largely on stereochemical arrangement of functional groups

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33
Q

What is the definition of stereoselectivity?
And give an example we need to know

A

preferential formation of 1 stereoisomer over another in a chemical reaction
-Conjugate addition

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34
Q

in the conjugate addition of a Me group onto an aromatic ring where the stereochemical arrangement is 98% TRANS favoured what organometalic compound should be used as a reagent?

A
  1. Me2CuLi
  2. Followed by H+/H2O

Me Taken from Me2CuLi and added to aromatic in Meta position (98% TRANS) due to steric hinderence)

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35
Q

Enols and ketones are (——-) of each other?

A

Tautomers
Enols tautomerise to ketones

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36
Q

How do you make Organocopper reagent?

A

2MeLi + CuBr ——> Me2CuLi +LiBr

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37
Q

What does it mean is a reaction is stereospecific?

A

If the starting materials differ only in their configuration are converted into stereoisomeric products
e.g Dehydroxylation of alkenes
-Products always the same just isomers of each other

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38
Q

How can you control chemoselectivity?

A
  1. Number of eqs
  2. Time
  3. Chemoselective agents
39
Q

What is an example of a chemoselective agent?

A

NaBH4
Sodium Borohydride is less reactive than LiAlH4, it reduces both ketones and aldehydes NOT esters

40
Q

Why is NaBH4 not as reactive as LiAlH4?

A

Na is not as e+ve as Al
Not as reactive
Not as strongly ionic

41
Q

What would the reagents be to convert:
O =[ Benzene] - Ester
to
HO-[Benzene]-OH

A
  1. LiAlH4
  2. Et2O
  3. H2O

*Both groups get reduced

42
Q

What would the reagents be to convert:
O =[ Benzene] - Ester
to
HO-[Benzene]-Ester

A
  1. NaBH4
  2. Et2O
  3. H2O
  • Ketone reduces
    *Ester unaffected
43
Q

What would the reagents be to convert:
O =[ Benzene] - Ester
to
O=[Benzene]-C(H2)-OH

A

Use protecting groups

*Ketone unaffected
*Ester reduced

44
Q

Why do we need to protect functional groups?

A

In order to react ONLY the least reactive group

45
Q

What makes a good PG?

A
  • Easy to install
  • Resists conditions that could damage functionality
    *Easy to remove under mild and specific condictions- that don’t affect other groups
  • Cheap + sustainable
46
Q

Why do PGs reduce atom economy?

A

They don’t appear in the final product

47
Q

What are orthogonal sets used to remove PGs?

A
  • Acid (HCl, HC3COOH)
  • Base (OH-, RO-)
  • Hydrogenation (H2, pd/c)
  • Fluoride ions (F-)

Ideally PGs only belong to 1 Orthogonal set

48
Q

What is the PG for Aldehydes and ketones?

A

2eqs of R’‘OH, which forms an acetal + H2O
-Diols are often used otherwise acetal formation is entropically unfavourable

49
Q

What is the mechanism for Protection of an Aldehyde or ketone using 2 eqs R’‘OH

A
  1. Protonate ketone
  2. react with OH = Nu attack
  3. Proton transfer
  4. Lose H2O
  5. React with 2nd OH
  6. Lose H+
50
Q

State the reagents requires to protect and deprotect a ketone whilst reducing an ester functional group?

A
  1. Diol + Cat. H+
  2. LiAlH4 + H2O
  3. H2O + Cat.H+
51
Q

What are the 3 things were trying to protect with PGs

A
  1. Ketones and aldehydes
    2.Hydroxyl groups (alcohols+Phenols)
  2. Amines
52
Q

What PG do we need to protect hydroxyl groups?

A

PGs belonging to the orthogonal set: ACID

53
Q

What are the Hydroxyl PGs?

A
  1. THP
  2. benzyl (Bn)
  3. Acetyl (Ac)
  4. (TBS)
54
Q

What do THP protected alcohols resist to?

A

Ox agents, Hydrogenation, Bases, Nu (grignards reagents), fluorides

55
Q

what are the conditions to protect and deprotect a:
primary alcohol <-> Acetal

A

Protect: Dihydropyran
Deprotect: H2O, Cat. H+

56
Q

What are the conditions to protects and deprotect a:
Primary alcohol <-> Ether

A

Protect: “BnBr”
Deprotect: H2, pd/c

PG = ‘Bn”

57
Q

What are the conditions to protect and deprotect a:
Primary alcohol <-> Ester

A

Protect: “AcCl”
Deprotect: Cat. NaOMe (base), MeOH (solvent)
PG =”Ac”

58
Q

What do Bn protected alcohols resist?

A

*Ox Agents
*Most Nu, Electrophiles and bases
*Fluorides

59
Q

What do Ac protected alcohols resist?

A

*Ox Agents
*Mild acids
*Electrophiles
*Fluorides
*Hydorgenation

60
Q

What are Ac PGs removed by?

A

Mild bases and Nu’s (Grig, Org.Li, LiALH4)

61
Q

What are the conditions to protect and deprotect a:
Primary alcohol <-> Silyl ether

A

protect: “TBS-Cl”
Deprotect: F- or H+

PG= TBS

62
Q

What do TBS protected alcohols resist?

A

*Ox agents
*Hydrogentation
*Electrophiles
*Most Nu’s

63
Q

What are TBS PGs removed by?

A

Flourides:TBAF (Tetrabutylammoniumfluoride)
Acid: TFA (CF3COOH)
(Trifluoroacetic acid)

64
Q

What do the reagents BU4, NF deprotect?

A

TBS

65
Q

What does the reagent H3O+ deprotect?

A

THP and TBS

66
Q

What do the reagents Cat. NaOMe and MeOH deprotect?

A

Ac

67
Q

What do the reagents H2 and pd/c Deprotect?

A

Bn

68
Q

what are good PGs for Amines, and why?

A

Carbamates,
*Easy to install
* Lp conjugated to carbonyl (Not Nu)
*Carbamates are not v reactive towards Nu’s
*Can be converted back to amines

69
Q

What would be a way to show why carbamates aren’t good Nu’s?

A

Show the resonance structure
-Lp Ends up in a +ve and -Ve charge on the molecule

70
Q

What are the conditions to protect and deprotect a:
Primary amine <-> “CBZ” carbamate

A

Protect: “Cl-cbz” , Na2CO3, H2O
Deprotect: H2, pd/c, MeOH

PG= cbz

71
Q

What do CBZ carbamates resist to?

A

*Ox agents
*Most E’s
*Acids
*Bases
*Most Nu’s (NOT grig, orgLi, LiAlH4)
*Fluorides

72
Q

What are the conditions to protect and deprotect a:
Primary amine <-> “BOC” carbamate

A

Protect: BOC, NaOH, H2O
Deprotect: Acid- TFA (CF3COOH)

73
Q

what do BOC carbamates resist to?

A

*Ox agents
*Most E’s
*Hydrogenation
*Bases
*Most Nu’s (NOT Grig, orgLi, LiAlH4)
*Fluorides

74
Q

Why is the deprotection of BOC and CBZ carbamates irreversible?

A

The bi-product CO2(g) will bubble off

75
Q

What are proteins?

A

polymers of AAs linked via peptide bonds

76
Q

What is the basic structure of all AAs?

A

Glycine

H2N-C-C(=O) - OH

The C next to the amine group is always chiral
All Have primary amines (except Proline which is 2nd)

77
Q

What is the C and N terminus of a peptide?

A

C = Carboxyl end
N = Amino end

78
Q

Why does peptide synthesis require PGs?

A

*If not an Acyl chloride would form (V. reactive and it would self react)
*Or a zwitterionic complex would form = No LP on the N = Not soluble in organic solvents

SO,
Any ‘R’ groups with any functionality must be protected
* If all reactive groups are protected then a peptide bond will form and HCl will be removed

79
Q

What coupling method is best for peptide sythesis?

A

DCC (need to know method)
-I think will come up on exam!
* Forms urea as side product

80
Q

When making an acid chloride why can’t BOC be used?

A

Because the conditions required also generate HCl
-ACID = no boc

81
Q

what conditions would you use to deprotect CBZ and ph and make a peptide?

A

H2, pd/C

82
Q

How would you protect analine’s N terminus

A

boc2O and NaOH

83
Q

How would you protect glycine’s C terminus

A

H-O-Bn and NaOH

84
Q

What is DCC

A

Its the combination of the BOC protected analine + Bn protected glycine

85
Q

How would you deprotect DCC?

A

CF3COOH (TFA), H+ and then H2, pd/c

86
Q

What is retreosynthesis?

A

Disconnect bonds you know how to make (e.g. esters) continues until you reach starting materials
-Working backwards

87
Q

What conditions do you need to go from Bn- C(H2)-Br to ph-C(H2)- MgBr

A
  1. Mg
  2. Et2O
88
Q

What conditions do you need to go from ph-C(H2)- MgBr to ph-C(H2)-C(CH3₂)-OH

A
  1. acetone (H3C-C(=O)-CH3)
  2. H2O ‘QUENCH”
89
Q

What conditions do you need to go from ph-C(H2)-C(CH3₂)-OH to
ph-C(H2)-C(CH3₂)-O-C(=O)-CH3

A
  1. Acid chloride
  2. Pyridine (weak base added to trap HCl generated during ester formation)
90
Q

where do you disconnect in retrosynthesis?

A

At branching points and remove chains from rings if possible
* Look for symmetry

91
Q

In the forward step what must you remeber to mention

A

QUENCH

92
Q

what size of compound should you try break down into

A

7 carbons or less
-Only 1 functional group

93
Q

What is a synthon

A

A generalised and frequently imaginary fragment produced by a disconnection

94
Q

Synthons and their synthetic equivalents
1. R+
2. R-
3. 2nndary alcohol cation
4. R-C(+)=O

A
  1. RBr/ RI
  2. RMgBr/ RLi
  3. ketone
  4. Acid chloride

Chemistry 2 (7 decks)

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