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Wittig-type Reactions - Larock p. 327-350 1,2-Disubstituted Olefins
Metathesis Reactions - Grubbs group Tri & Tetrasubstituted olefins (see other handout)
Elimination Reactions - Larock p. 251-315 Terminal Olefins (see other handout)
O
R'
R
RRR R
YX
R
R3P
R''
R'''
R'
R
RR
R
R'
R
R''
R'''R'
R
R
R
R
RR
R
R
R
R R
R
RR
reagent
+E Z
+Catalyst
Olefin Synthesis
-Plethora of references in the literature on olefin synthesis: see Larock 2nd ed. p. 215-562
-These can be catagorized by reaction type: -Or categorized by the olefinic product:
Chem 6352Jeremy May
Note: these are much more difficult because of E/Z issues!
IV
III
II
I
R R
H N N H
Cr
CO
CO
CO
HBR2
H
R R
BR2
RR
OMe
AcOH
CO2Me
OH
R R
H
R R
H
1,2-Disubstituted Olefins
•Z-olefins
Lindar's Catalyst, H2
Diimide reduction
, H2 (JOC 1985, 30, 1147)
Hydroboration/Acidic Quench
-From Acetylenes: by reduction
-From Rings:
O3, NaBH4
Pd/BaSO4, Quinoline (partially poisons catalyst)
S+
-
O-
P
O
PhPh
Ph
H
HR
R'
Base: nBuLi, LDA, KHMDS, NaHMDS, LiHMDS, tBuOK, , etc.
(DMSO, NaH)
R X
R PPh3
PPh3
O
R'
H
H
Ph3P
RC HPh3P
R
OH
R
R PPh3
R PPh3 X
H H
R' H
O
C HPh3P
R
OH
R'
R H
HR'
R R'
Ph3P O
R PPh3
OH
R'
Ph3PH
R
-From Wittig Reaction:
preparation of ylide:
+Δ
Polar Solvent(THF, acetone, EtOH, MeCN)
pKa ~22
base
mechanism of the Wittig reaction: Chem. Rev. 1989, 863 JACS 1989, 6861 JACS 1981, 2823
Antiperiplanar
Kinetic Reaction Preference Betaine
Oxaphosphetaine
+
Vedejs
alkyl halide
R H
OLi
R H
O
Ph3P
Ar
H
I I
R H
O
Ph3P
H
I
PPh3
P
Ar
H
O
MeO
R H
O
R Ar
R Ar
R I
RAr
RAr
N
N
LiN
N
-Salt Effect:
Activation of the carbonyl by a Lewis acidic salt can increase the reaction rate and lower the selectivity. Also, it leads to a more open transition state (ie. there are fewer steric effects).
-To counter the effect:
Additives: HMPA, TMEDA → these break up and sequester lithium ions
Freeze/filter salts: becomes difficult preparatively.
-Examples: (Stork TL 1989, 30, 2173)
+ Very useful for Stille/Heck reactions.We will see this again later!
+ + base
-Phosphine effect: Synlett 1990, 605
+ +
Z E
Z form is slightly favored
+ +
Z E3
Z:E = 96:4
I
OTHP
O
OH
THPO
o H
DMSONaH
Ph3PCO2H
1)
2) PhLi, then MeOH, -30 °C
R +PPh3PhLi R
PPh3R' H
O
+Li
-O
+PPh3
-Br
H HR R'
Ph-Li
+
+Li
-O
+PPh3
-Br
H R'R
OO
O O
PPh3
Br-
H+
(MeOH)
OO
O O
RR'
OTHP
HO
THPO
CO2H
+Li
-O
+PPh3
-Br
H R'R' H
The Schlosser Modification of the Wittig: reversal of selectivity for non-stabilized ylides.
1)
2) PhLi (-70 → -30 °C)3) MeOH or tBuOH (-30 °C)
warming (-30 °C)
W. S. Johnson, Progesterone Synth. JACS 1971, 93, 4332
97:3 trans:cis
-The Reaction of Lactols: (Corey, JACS 1969, 91, 5675)
ACIEE 1966, 5, 126Synth. 1971, 29Liebigs Ann. 1967, 708, 35
1) CuBr•DMS Et2O, -20 °C
2) E
R Li
R'' M
R H
H
H
R
R'
OH H
O
AlMe2
R
Me
R'' R
R'M
R H
HE
R'' R
R'E
I
R
MeI2
orE
-Carbometallation:
More Z-olefin formation:
E
-Copper/Magnesium:
+
+
E=I2, ,
There will be more examples with the trisubstituted olefin section.
-Zirconium/Aluminum:
Me3Al
Cp2ZrCl2
BrH SiEt3
R H
Br
Br
SiEt3
H
R
H
Br
MeR
Br
SiEt3
HBr
RH
R'R
RI
Me2CuLi"Gilman Reagent"
BrR
BrR
Br2
Br2
H
R H
SiEt
Et3SiH
PtCl2
HR
-Hydrometallation/Halogenation:
TL 1981,22,315TL 1986,27,4351Org. Rxn. Vol. 41 (Lipschutz)
Hydrosilylation
Pd mediatedreactions
Further reaction of the vinyl bromide:
Note: treatment with I2 gives .
I
H BR'2
R H
I
H B
R HOH
R'R'
H H
R R'
I
B OHR'
HO
HO
H
R'
H
RI2
NaOHH
R H
BR'2
I2
H B
R HOH
R'
I
R'
R'2 BHR H
-Hydroboration/Alkyl transfer:
+
Note: One R' group will be wasted!
n
R' R'R
n
N
Mo
CH3C(CF3)2OCH3C(CF3)2O
i-Pri-Pr
Ph
CH3CH3
Ru
PCy3
PhCl
Cl
NN
Ru
PCy3
PCy3
PhCl
Cl
X
RCM
X
X
ROMP
ROM
X
R
X
R1
R2
CMR1
R2
n
ADMET
- C2 H
4- C
2H
4
Diene Metathesis Reactions Terminal Olefin Intermolecular Reactions
- C2H4
•E-olefins: 1,2-disubstituted olefins continued
From Olefins: Olefin Metathesis
Schrock JACS 990, 112, 3875Grubbs Acc. Chem. Res. 2000, 34, 18
R1
R1
[M]R
R2
R2 R2
R1+
= Metal Alkylidene
[M]R
[M]R
[M]R
[M]
R1R1
R
R1
R [M]
R1 R2
R2 [M]
R2R1
R2
+
Typically a thermodynamic equilibrium process.The reaction produces a new carbon-carbon double bond.
-Mechanism of Olefin Metathesis:
OH OH
NHO
S
O
O Me
NO
O
NH
H
Ar
CHO
Si(OR')3
B(OR')2
RSi(OR')3
H
H
RB(OR')2
H
H
RCHO
H
H
Macrocycle formation:Meyers ACIEE 2000, 9, 1664
Griseoviridin
O ClMg
RH
H
H
HO
RAr
H
H
HO
Examples:
Mixture of diastereomers
Cross Metathesis:Grubbs ACIEE 2002, 41, 3174
Ring closing for meduim reings: Furstner JOC 1996, 61, 8746
Dactylol
Substitutedstyrenes
Unsaturated aldehydes
Vinylsilanes
Vinylboronates
Ru
PCy3
PCy3
PhCl
Cl
Ru
PCy3
PhCl
Cl
NN
N
Mo
CH3C(CF3)2OCH3C(CF3)2O
i-Pri-Pr
Ph
CH3
CH3
Olefin Categorizing for Selective Cross Metathesis
Vinyl boronates
Terminal o lefin
Styrene
Styrenes (no large ortho substit.)
Styrenes (large or tho substit.)
Term inal ole fins, 1° a llylic a lcohols, esters
Allylboronate esters, A llylic halides
2° allyl ic a lcohols
Acrylate esters, amides, acids,
aldehydes, and vinylketones
Allyl phosphonates, phosphine oxides,
sul fides, protected am ines
Al lylboronate esters
Vinylsi loxanes
Per fluorinated a lkane o lefins
1,1-Disubstituted ole fins
Vinylphosphonates
Phenyl Vinyl Sulfone
4o a llylic carbons (a ll alkyl substituents)
3o a llylic alcohols (protected)
Type 1
Type 2
Type 3
Type 4
1,1-disubstituted ole fins
Disubsti t. α,β-unsaturated carbonyls
4o al lylic carbon conta ining o le fins
Perfluorinated alkane ole fins
3o al lylam ines (protected)
Trisubstitu ted a llylic alcohols (protected)
Olefin type
(fast
homodimerization)
(slow
homodimerization)
(no homodimerization)
(spectators to CM)
Acrylon itr ile
Terminal ole fins
Allylsi lanes
Styrene
Allylstannanes
1,1-disubstitu ted o lefins
1 2 3
Vinyl n itro o lefins
Tertiary a llylamines
Allylsilanes
1° a llylic alcohols, ethers, esters
Allylhalides
2o a llylic a lcohols
Unprotected 3° allylic alcohols
Vinyl epoxides
Vinyl d ioxo lanes
AlO
RH
PhMe
HMPA-78 → -10 °C
O
H
CO2Me
From Aldehydes:
Wittig Reaction: Modifications to give E-selectivity
-Internal basic group promotes E-selectivity
Ph3P
O
+
R R
R
OH
Li, NH3(l) RR
H2O R OH
CO2Me
HO
From Acetylenes:
LAH
dioxane100 °C
JACS 1978, 100, 1942Corey Ch. 11 - Prostanoids Ch. 12 - Leukotrienes & EicosanoidsNicolaou ACIEE 1991, 30, 1100
Li
→
R'
R
Normally Kinetic
HPh3P
R'
R'
R
10% NaOH
H2O
1)BuLi
2)
100 °C
O H
R
Z-olefin
E-olefin
H
O
Ph3P
R'H
R
H
O
R'
Ph3PH
R
H CN
PPh3PPh3
O
ORH
Ph3P RBr
P R
O
Ph
Ph
PPh2Me
H R'
R' H
O
PPh2
H
RR'
PPh3
EWG H-Electron Withdrawing Group (EWG) on Wittig Reagent:
Consider the mechanism:
equilibration
Stabilization of this anionby EWG as R' will favor theultimate thermodynamicproduct.
Examples:
or
also: Phosphine oxides: S. Warren JCSPT1 1985, 2307 (Horner)
+
VedejsJOC 1984, 49, 210Synth. 1988, 911Corey and LazerwithJACS 1998, 12777
P(OR)3
P CO2R
O
RORO
R
P CO2R
O
RORO
P CO2R
O
RORO P
O
RORO O
R H
O
P
O
H
R
H
CO2ROR
RO
OP CO2RO
RO OR
OR
H
H
P
O
RORO CH2
THF
-78 → 0 °C96%
P
O
RORO R
O
Br
M
, base
equilibrium
BrOR
O
RO R
O
O
OR
R
-Horner-Emmons-Wadsworth Modification
Arbuzov Rxn:
Phosphonate
HEW Rxn:
+
Also:
+
see Nicolaou amphotericin synthesis in Classics of Total Synthesis (many other examples).
R H
O
R H
O
O M
O
H
P ORO
RO
OR
R
H O M
O
H
P ORO
RO
OR
R
H
KHMDS18-crown-6
THF>95%
P
O
H
R
RO2C H
OOCH2CF3
OCH2CF3OR
OOM
R
PO
OCH2CF3
OCH2CF3
R
O
OR
OR
OOM
R
PO
OCH2CF3
OCH2CF3
P CO2MeF3CH2CO
O
POR
OO
RO
RO
M
-Still Modification of the HEW reaction: TL 1983, 24, 4405
2
Z-selective enoate synthesis
>50:1
irreversible, anda late transition state
fast
syn-aldol product
Transition state that leads to the syn-aldol stereochemistry.
CHI3 (Iodoform)
CrCl2THF/dioxane
4:1
1) I2
2) CrCl2, Zn, DMF3)
R O
H
N
H
R
NH2
R
H
I
I
R'O
H
RI
CrCl2
RR'
-Takai Reaction:
many uses
>20:1 stereoselectivityNicolaou - Rapamycin Synthesis
Also:
95:5 E/Z
JACS 1986, 108, 6048JACS 1987, 109, 951
IH
CrII
CrII
proposed active intermediate
R
H
CrII
CrII
PhO2S Li
Me Me
OTBDPS
O O
Me
Me
H
Me
OTBSMeHMe
O
O
OH
R SO2Ph R
SO2Ph
R'
OHAc2O R
SO2Ph
R'
OAc
RR'
OAc
Na(Hg)
MeOH
O O
Me
Me
H
Me
OTBSMeHMe
O
O
Me Me
OTBDPS
RR'
RR'
OAc
-Julia Olefination:
BuLi
+e-
+e-
This elimation produces the thermodynamic product.
The reduction step is not stereospecific.
Phosphorus & Sulfur 1985, 24, 97JCSPK1 1978, 834Bull. Ch. Soc. Jpn. 1988, 61, 107
Evans: JACS 1990, 112, 5290Ionomycin Synthesis
1) add RCHO, -78 °C add AC2O, -78 °C to R.T.
2) Na(Hg), EtOAc/MeOH, -30 °C
70% yield86:14 olefin mixture
O
R'H
Peterson:Ager:
JOC 1968, 33, 780Synth 1984, 384
O
OTMS
TMSO
Me
Me
O
O
Me
OTMS
1) KN(SiMe3)2, <50 °C
2)
3) H+, THF/H2O
O
N
N O
Me
SiMe3
(R1)3Si
H
R3R2
RLi
O
OTMS
TMSO
Me
Me
O
Me
OTMS
O
N
N O
Me
(R1)3Si
Li
R3R2
R5R4
O
R3
R2 R4
R5
(R1)3Si O
R3 R5
R2 R4
(R1)3Si OH
R3 R5
R2 R4
H2O
(R1)3Si
R3 R4
R2 R5
OH2
R3
R2 R5
R4
base acid
-Peterson Olefination:
Conditions control the stereospecificity of the elimination reaction, but the initial stereochemistry of the addition to the carbonyl must also be controlled to produce E or Z olefins specifically.
Tetrahedron 1994, 50, 6643
90% yield13:1 E:Z
For practice:What is the required stereochemistry for each step of the mechanism?
R
R'
OH
R
O
O
R'
R
O
OTMS
R'
O
OTMS
R'
R
H
TMSO R
R'
O
O
OTMS
R
R4
R3
R1
R2
O
TMSO
R4
R
H
R2
R1
R3
O
OTMS
R'
R
H
O
TMSO
R4
R
H
R2
R1
R3
H
TMSO R
R4
O R3
R2
Claisen Rearrangement: (more at the end)
Ireland-Claisen: very powerful reaction
Equatorial in TS!
LDA/TMSCl
trisubstitutedif R' ≠ H
trans olefin
Of Note:
Recall: Enolate geometry arguments•Esters + LDA → E-enolates•Esters + LDA + (HMPA or DMPU) → Z-enolates
Subst. at R1 → Z-enolateSubst. at R2 → E-enolate
Two new stereocentersand
trisubstituted olefin
H
H
I
II
III
P
O
RO OEt
O
2
KOtBu, THFH
O
O
OTMS
R'
R
OEt
O
O
OTMS
R
R'
R''
R H
R'''
CO2Et
Trisubstituted Olefins
2,3 and 3,3 rearrangements (eg Wittig, Claisen, Cope, etc.)In fact 3,3 rearrangements are among the best methods.
Wittig Rxns: Typically not very selective (if R' and R'' are different).some examples with stabilized reagents: Kishi TL 1981, 37, 3873JACS 1979, 101, 259
From acetylenes by metalation reactions
+
R= MeiPr
CH2CF3
95 : 5 5 : 95 1 : 50
Still a serious stereochemical problem.
Acetylenes/Propargyllic alcohols
-With aluminum reagents:Corey:JACS 1967, 89, 4245JACS 1970, 92, 6314JACS 1968, 90, 5618
R
OH
1) LAH, NaOMe (1:2) Et2O or THF
2) I2
Reduces the Lewis acidityof any Al species.
Must be freshlyprepared!
OAl
R H
I
R
OH
R'2CuLi
R'
R
OH
R
OH
-If there is a small amount of Lewis acid present:
1) LAH, AlCl3 (60:1) 2) I2 H
R OH
I
R'2CuLi R OH
R'
Maybe ???
R
OAl
Cl Cl
ClHH
R
Al
O
Cl
Cl
→
R H
OEtMgBrCuI
Et2O
E
E orMe3Al
Cp2ZrCl2CH2Cl2 or ClCH2CH2Cl
R H
O
E
Br
"EtCu"
E = H , I2, ,Et
R
Cu Et
R
E
R
R
Me
R
AlMe2Me
R
R
HO
ZrClCp
Cp Me
ClRR
ZrMe
Cp
Cp
R
ZrMe
Cp
Cp
R
ClZr
Cp
Cp MeZr
Cp
CpMe
Me2Al
Zr Cl
Cp
Cp
Me
R
Me2Al
-With organocopper reagents:
terminal acetylenes: Org. Synth. VII 236-240
Negishi Protocol: JOC 1980, 45, 2526JACS 1981, 103, 1276JACS 1981, 103, 4985
CatalyticProduct
I2Swartz's Reagent
ZrClCp
Cp H
LAH
Swartz's Reagent
RL MeH
RL Me
ZrCp
CpCl
RL Me
I
-Schwartz Hydrozirconation Reaction:Jeffrey Swartz (Princeton)
Cp2ZrCl2 Will not react with olefins!
TL 1987, 28, 3895TL 1990, 31, 7257
Hydroboration is not as selective between olefins and alkynes.
Pd(0)
Bu3SnSnBu3
LiCl
RI
COPd(0)
1) LDA, Tf2NPh
2) Pd(0)
OO
Pd(0)
Et3SiHPd(0)
orBu3SnH
Pd(0)
COPhSnBu3
H
Me3Sn
OO
O
Me3Sn
OO
TfOOTIPS
OtBu
OTf
Bu3SnOTIPS
OtBu
OTf
Me3Sn
OO
Ph
O
OTIPS
OtBu
R
O
Enol Triflates: JOC 1986, 3405
McMurray TL 1980, 21, 4313
Also: JACS 1993, 115, 9293
NN
SO2ArLi
Li
LiN2
NN
-Also acyclic examples: TL 1997, 38, 8915TL 1997, 38, 8919
NN
SO2ArLi
Li
NN SO2Ar
Li
OMe
NN
SO2ArLi
Li
Ar
Ar
Li
Ar
I
warm- N2
- LiSO2Ar
OMe
BrnBuLi
(2 equiv)
N
HN SO2trisyl
OMe
S ArO
O
Li
warmN
HN S
O
O
Li E
Shapiro Reaction Ex: Pacquette JOC 1980, 45, 3017Also: Sorenson
nBuLi (2 equiv)
-78 °C
golden yellowsolution
E
•trisyl group: prevents o-lithiation and nucleophilic attack at S
Corey and Roberts
nBuLi
64% yield
golden yellowsolution
-Z-enol Silyl Ethers: TL 1997, 38, 5771JACS 1996, 118, 8765
Li
R-X
Brook
RearrangementAr
O Si
BaI2
- I
1)
Et2O, -78 °C2) BaI23) R-X
Li
Ph
OSi
TBS
O
Li
Ph
TBSO Li
Ph
OTBS
BaI
OTBS
R
Tetrasubstituted Olefins
Corey
Acyl silane
PhOBn
NR
PhOBn
NR
PhO
NN
Ph
PhO
NR
O
O
Ph
R'R
RhLn
HHRh2(OAc)4
H2N N
Ph
OPh
O
O
Ph OBn
OPh
OBnPh
N2
1 70 1:0
2 81 1:0
3 63 1:0
69 1:04
R'
O
R
R'
NN
Ph
RR'
N
R
N
RR'
Substrate Product Yield Z:Eentry
Applications of Olefin Synthesis:The Bamford-Stevens Reaction
JACS 2002, 124, 12426
Results in the lab: Can this reaction be made more powerful?
1,2-Hydride
shift
H
O
Ph
Rh2(OAc)4
R1
O R4
N
R2
R3
R5
NPh
Δ
O
NN
Ph
OR1
R5
R4
R3
R2
[O]
HO R2
R1 R3
R4 R5
H R2
O
R1 R3
R4 R5
Bamford-Stevens
Claisen
(iBu)2AlH
-15 °C
iodolactonization
O
I
O
Ph
Δ or
Me2AlCl-45 °C
Coupling of the Bamford-Stevens reaction to a Claisen Reaction
R1 = Ar, vinyl, or alkyl
Yields: 63-87%
de: 75-99%
Mono, Di, and Trisubstituted olefins are accesible
As seen previously, aldehydes offer access to many transformations:
α-allyloxysubstituent
BS Claisen
H
O Ph
O
Ph
H
BS Claisen
OH
Ph
NR
O
NR
O Ph
Ph
H
O
Bamford-Stevens/Claisen/Ene
Bamford-Stevens/Claisen/Cope
Ene
Cope
68 % yield>20:1 dr
68 % yieldone isomer for
both olefins
Coupling of the Bamford-Steves Claisen to the Cope and Ene Reactions:
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