Παρουσίαση Beretta Stoeger Synthetic Κυνηγετικά Νέα 18.09.2013
M.Sc. 3rd sem Advanced Organic Chemistry Synthetic reagents
Transcript of M.Sc. 3rd sem Advanced Organic Chemistry Synthetic reagents
Synthetic reagents
Dr. L. Satish Kumar Achary
Asst. Professor
Department of Chemistry
CV Raman Global University
Advanced Organic ChemistryM.Sc. 3rd sem
Organometallic reagents
Contents
➢ Organosilicon
➢ Synthesis.
➢ Applications.
➢ Organotin
➢ Synthesis.
➢ Applications.
➢ Tebbe reagent2
❑ Organosilicon
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Trimethylsilyl chloride
(TMSCl)
tert-butyldimethylsilyl chloride
(TBDMSCl)
Diphenylmethylsilyl
chloride (DPMSCl)
Triisopropylsilyl chloride
(TMSiCl)
SiSi
Si Si
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❑ Si forms weaker bond with electropositive elements w.r.t C.
❑ Si has low E.N than C. Thus C-Si bond is polar.
❑ C-Si bond length 1.89 Å, steric interaction between Nu- and
substrate is less. C-C bond length 1.53 Å.
❑ Silicon has vacant d-orbital which provides a target for Nu-.
C-Si
C-F
C-Cl
C-OH
F-
Cl-
OH-
StableNaF, HF, KF, nBu4NF,
NaCl, HCl, NaOH,
KOH
❑ Silicon stabilizes α-carbanion with vacant d-orbital and β-carbocation with σ-bonding orbital.
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❑ Synthesis
SiCl4
Chloro compounds are the starting materials for the preparation of
organosilicon compound.
3CH3MgCl (CH3)3SiCl+
❑ Applications
(1) As nucleophilic reagent for O-C bond cleavage
Ether reacts with the reagent to afford the alkyl iodide and
trimehylsilyl ether.
+ +
+
Ether
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+
TMSI TMSI
Epoxide
Epoxides give corresponding alkene.
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Acetal
Acetal can be converted in to ketones.
(2) In nucleophilic addition reaction
Addition reaction with carbonyl compound.
α-iodotrimethylsilyl ester
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(3) Protecting group for alcohols as TMS ester
TMSCl (1.2 equvalent) TMSCl (1.3 equvalent)
t-butyldimethylsilyl halide (TBDMS-X) is a bulky reagent which
preferabily protect primary alcohol with imidazole in DMF.
TBDPSCl
Imidazole/DMF
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1. TBDMSC
2. DDQ
3. Cl-
Deprotection can easily be done by the treatment of tetra-n-
butaylammonium flouride (TBAF), citric acid and Cl-.
TBAF/Et3N
CH2Cl2
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Silylenol ethers
Trimethylsilyl enol ether of aldehyde and ketones are usually
formed from carbonyl compound. An additional base is used.
Me3SiI/Et3N
DMF
Me3SiI/Et3N
DMF
Product depends upon base.
If base is bulkier, less substituted sillyl enol ether is the major
product. (LDA)
If base is small, more substituted sillyl enol ether is the major
product. (Et3N)
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Regioselectivity
Alkylation of carbonyl compound
1.Base, 2. R3SiX
3. R-X, 4. H3O+
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1.LDA, 2. Me3SiX
3. CH3-X, 4. H3O+
1. Et3N, 2. Me3SiX
3. Ph--X, 4. H3O+
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Peterson’s olefination (α-carbanion)
Li-Mg derivative of α-silylCarbonyl
CompoundOlefins
Alkenyl silane(β-carbocation)
Alkenyl silane undergoes electrophilic substitution reaction via β-
carbocationE+
E+X-
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Electrophillic substitution reaction catalyzed by Lewis acid.
AlCl3
AlCl3
AlCl3
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Allyl silane (β-carbocation)
E+ X-
Allyl silane undergoes electrophilic substitution reaction via β-
carbocation.
Electrophillic substitution reaction catalyzed by Lewis acid.
AlCl3
AlCl3
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Bu3–Sn–HTributyltin hydride
❑ Organotin
Sn has more metallic character with +4 oxidation state and forms
stable organic compounds.
Size if Tin is larger than Si and C due to which the bond between
Sn and C can be easily polarized.
❑ Synthesis
4Bu3SnCl
Tributyltin hydride is prepared from tributyltin chloride and LiAlH4.
LiAlH4+ 4Bu3SnH LiAlCl4
+
Tributyltin hydride is generally used as reducing agent and used
as source of hydrogen radical.
Initiator: AIBN (Azobisisobutyronitrile).
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❑ Applications
(1) Replacement of halo group
Tributyltin hydride replaces halo group from all organo halo
compounds.
R-X R-HBu3Sn-H
AIBN
X = F, Cl, Br, I.
Bu3Sn-H
AIBN
Bu3Sn-H
AIBN
Bu3Sn-H
AIBN
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Bu3Sn-H
AIBN
Bu3Sn-H
AIBN
Reactivity order
Benzyl halide > allyl halide > 3° alkyl halide > 2° alkyl halide >
1° alkyl halide > aryl halide > Vinyl halide > Alkenyl halide.
Bu3Sn-H
AIBN+ +
If halocompound having unsaturation, substitution may
accompanied by cyclisation.
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Bu3Sn-H
AIBN +
Bu3Sn-H
AIBN
(2) Replacement of nitro group
Tributyltin hydride replaces nitro group from new C-C bond.
Bu3Sn-H
AIBN
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(2) Replacement of sulphide group
Bu3Sn-H
AIBNR-SR1 R-H
Bu3Sn-H
AIBN
Bu3Sn-H
AIBN
Bu3Sn-H
AIBN
If there is an unsaturation in the sulphide, replacement of sulphide
followed by cyclization takes place.
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(2) Reduction of acid halide
Bu3Sn-H
AIBN
Acid halide gives aldehydes.
(3) Reduction of carbonyl compound
Bu3Sn-H
AIBN
Bu3Sn-H
AIBN
Carbonyl compound converted into alcohol.
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❑ Tebbe reagent
❑ The tebbe reagent is the organometallic compound.
❑ It is used in the methylenation of carbonyl compounds.
❑ Formula :C13H18AlClTi
❑ Synthesis
Titanocene dichloride reacts with trimethyl aluminium in toluene.
Me3Al
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❑ Applications
❑ Methylation of carbonyl compound
base or
without
base❑ Mechanism in presence of base
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❑ Mechanism in absence of base
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❑ Methylation of amides
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❑ Reactivity of carbonyls
> > >
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1 eq.
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