Homework Assignment 8

CHEM 203
HOMEWORK 8
Ethers, alcohols
1. Write the structure of:
a. An alkyne containing at least 4 carbon atoms that will give one epoxide when treated H2 and Lindlar
catalyst followed by MCPBA, but an isomer of the first epoxide when subjected to Na / NH3(liq)
followed by MCPBA.
e.g.,
b. An epoxide that gives an achiral product when treated with H2SO4 and H2O, but a chiral product when
reacted with H2SO4 and CH3OH.
H
O
e.g.,
H
2. Complete the synthesis diagram shown below by indicating the structures of products A – E, and write
accurate mechanisms for their formation.
1. CH3MgBr
1. NaNH2
(1 equiv.)
2.
H C C H
2. CH3–CH2–I
A
O
3. mild H3O+
HO
B
1. Na / NH3 (liq)
2. mild H3O+
HO
C
N
H
H
OH
1. TsCl, pyridine
1. OsO4
2. aq. NaHSO3 C
N
E
D
2. NaCN
OH
C
mechanisms:
H C C H
NaNH2 ≈ Na+
O
NH2
H C C
Na+
H C C
CH3–CH2–I
CH3MgBr ≈ CH3
HO
MgBr
H–OH2
BrMg
reacts with Na . . .
MgBr
Na / NH3 (liq)
O
NaO
e–
C C
CHEM 203
HOMEWORK 8
Na+ NH2
H–NH2
Na+
ONa
ONa
p. 2
ONa
e– Na+
Na+ NH2
ONa
H–NH2
Na+
H–OH2
N
C
O
O S
H
O
N
HO
O
N S
O
O
O S
O
NH
Cl –
Cl –
Cl –
N
O
Cl S
O
N
N
H
H
HO
C
H
H
N
C
O
O
Os
O
O
C
O
O
Os
O
O
aq. NaHSO3
(no mech.)
OH
3. Write detailed mechanisms for the following reactions:
a.
HO
HO
cat. HBF4
OH
50 °C
H2SO4
b.
O
OH
heat
O
CHEM 203
HOMEWORK 8
OH
Br
Zn
c.
d.
Br
p. 3
1. H2SO4, 160 °C
2. O3, then Zn/H+
3. excess CH3MgBr
H3O+
4. mild
5. excess TsCl, pyridine
6. Na2S
H
S
+
H
(meso)
H
S
H
(racemic)
CHEM 203
HOMEWORK 8
p. 4
CHEM 203
HOMEWORK 8
p. 5
CHEM 203
HOMEWORK 8
p. 6
CHEM 203
HOMEWORK 8
p. 7
4. Complete the following equations by indicating all the reagents, in the correct order, that are required to
achieve the desired transformations (more than one step may be necessary).
1. Cl2, hv
2.
1. HBr
2. Mg
a.
D
3. O3
b.
4. Zn / H+
5. NaBH4
6. PBr3 (e.g.)
7. HC C–Na
3. D2O
1. PBr3 (HBr OK)
2. Mg
3. add to A, then
mild H3O+
c.
O
d.
OH
4. H2SO4, heat
5. BH3
PCC
(or Jones) 6. H2O2, aq. NaOH
OK
OH
1. NaBH4
2. H2SO4
heat
3. H2, finely
divided Pd
O
A
5. Predict the structure of the major product arising from each of the following reactions and write accurate
mechanisms for its formation.
H
a.
OH
1. PBr3
2. CH3-CH2-MgBr
CuI
CHEM 203
HOMEWORK 8
1. PCC
2. CH3Li
OH
p. 8
Br
b.
via:
then mild H3O+
3. HBr
H
O
H
O
H
O
O
O
Cr
O
Cl
O
Cl Cr O
O
O
Cr
O
O
± H+
Br–H
OH
H2O–H
O
Li +
O
O
H
CH3–Li ≈
Br –
OH
c.
CH3
Br –
Br
OH2
1. H2SO4, 180°C
2. Br2, H2O
3. NaH
O
via:
4. CH3-CH2MgBr
CuBr
5. mild H3O+
6. Jones rgt.
+Li
O
Cr
O
OH
CHEM 203
HOMEWORK 8
p. 9
H2O
OH
H–OSO3H
OH2
H
NaH ≈
Na+ H–
O
H–O
H
H2 +
H
Br
Br
Br
Br
OSO3H
± H+
OSO3H
Br –
Br
H
O
CH2-CH3
H
H
MgBr
H
H–OH2
O
( CuBr )
O
HO Cr OH
OH O
H
H
HO
OH
O Cr
OH
H
O
O
±
H+
H
H O
OH
O Cr
HO O
H
1. MCPBA
2. cat. H2SO4
d.
OH
H
O
via:
3. TsCl, pyr
4.
Br –
H
BrMg-CH2-CH3 ≈
H
H
Br
H
H
H2O
H
H–O H
OK
Cl
O
O
O
Cl
OSO3H
OH
O
H–OSO3H
O
H
OH
OH
HO
O
O
E2
OH
OH
K+
O
H
± H+
OTs
H
OH
TsCl, pyridine
O
(mechanism:
see problem 2)
O
CHEM 203
HOMEWORK 8
p. 10
6. Propose a synthesis of the compounds shown below starting only with 1-butanol [ CH3-(CH2)3-OH ] as the
source of carbon atoms. You may use any additional reagent that might be needed (e.g., borane, HCl, Mg,
etc.)
H2CrO4
aq. H2SO4
O
a.
OH
OH
(Jones rgt.)
H2SO4
OH
b.
O
O
OH
PCC or
c.
mild
Jones
PBr3
OH
OH
180 °C
H2SO4
O
MgBr
H3O+
Mg
Br
MgBr
PCC
OH
MgBr
O
Br
Mg
OH
PBr3
d.
O
HBr
part c.
Br
Mg
MgBr
part b.
PCC or
e.
MgBr
Jones
O
OH
part d.
O3, then
H
O
Zn / H+
part b.
CHEM 203
HOMEWORK 8
p. 11
7. Propose a synthesis of the compounds shown below starting only with 1-butanol and propyne as the source
of carbon atoms. You may use any additional reagent that might be needed. It is understood that chiral
products will emerge in racemic form.
OH
H
a.
H
OH
OsO4
H2, Lindlar
then aq.
NaHSO3
catalyst
OH
H
H2, finely
OH
b.
PBr3
Br
NaNH2
Na+
OH
Na+
O
part a.
divided Pt
H
O3, then
Zn / H+
H2SO4
OH
Cl
c.
H
H
Cl2
180 °C
H2, Lindlar
Na+
Br
part a.
catalyst
Cl
PBr3
O
NaBH4
OH
H
part b.
PCC or
d.
PCC
O
Jones
O
HO
OH
MgBr
H2, Lindlar
HBr
Br
Mg
catalyst
OH
e.
H2, Lindlar
catalyst
OH
Na+
part a.
O
part d.
CHEM 203
HOMEWORK 8
p. 12
8. Propose a synthesis of the compounds shown below starting only with propyne as the source of carbon
atoms. You may use any additional reagent that might be needed (e.g., borane, HCl, Mg, MCPBA, etc.)
OH
PCC or
O
a.
OH
Jones
Na+
H2SO4
H2O
H2, Lindlar
catalyst
NaNH2
O
b.
cat. H2SO4
O
O
+
OH
– H2O
O
2. aq. NaHSO3
(part a.)
a ketal . . .
H2, finely
OH
PCC or
c.
1. OsO4
OH
Jones
OH
divided Pd
Na+
MCPBA
O
(part a.)
H
Br
H2, Lindlar
Br2
d.
Br
(part a.)
H
catalyst
Na+
HBr
(part a.)
rad. init.
Br
(part a.)
other approaches may be OK
(part a.)

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