Synopsis
CHAPTER-I
SECTION-A: Total synthesis of mevinic acid analogue.
Microorganisms make a wealth of unusual metabolites that have a secondary role in
the organism’s ontogeny, such as a self-defence, aggregation, or even communication, as
the need arises. Polyketides are a group of secondary metabolites, exhibiting remarkable
diversity both in terms of their structure and function. Posses know Polyketide natural
products a wealth of pharmacologically important activities, including antimicrobial,
antifungal, antiparasitic, antitumor and agrochemical properties. These metabolites are
ubiquitous in distribution and have been reported from organisms as diverse as bacteria,
fungi, plants, insects, dinoflagellates, mollusks and sponges.
Here we described an efficient and stereoselective synthesis of mevinic acid
analogue from (R)-2,3-O-isopropylidene glyceraldehyde 2. Wittig reaction, cyanation are
the key steps involved in our synthesis. The retrosynthetic analysis for mevinic acid
analogue may be represented as shown in (Scheme 1.)
O
OH
O
OH
OH
OH
14
1
O
CO2Et
CO2Et
13
OH
OTPS
OH
CHO
Wittig reaction
D-mannitol
11
5
Scheme 1
Our synthesis began with the chiral aldehyde (2), obtained easily from D-mannitol,
which was subjected to a Wittig reaction to give compound 3, in 90% yield. Hydrogenation
of compound 3 over 10% Pd/C in methanol gave acetonide 4 followed on treating with
conc. HCl in methanol afforded diol 5 in 97% yield. At this stage the asymmetric center of
the secondary hydroxyl group in the diol 5was inverted by the Mitsunobu reaction to give
inverted diol 7 in order to match with stereochemistry of the hydroxyl in the natural product
I
Synopsis
1 at C-2′. The primary hydroxyl group in 7 was protected with tosylchloride using
triethylamine and catalytic amount of Bu2SnO to produce tosylated compound 8 in 79%
yield with the minor tosylation at the secondary hydroxyl group of 8. The tosylate 8 was
converted to corresponding nitrile 9 in 91% yield by the reaction of KCN in ethanol and
H2O (3:2) at room temperature. The secondary hydroxyl group in the nitrile 9 was protected
with TBDMSCl/imidazole to give tertiary-butyldimethylsilyl ether 10 in 98% yield. The
nitrile function was reduced with DIBAL-H in dry dichloromethane at -78 0C to afford the
aldehyde 11 in 70% yield (Scheme 2).
O
O
O
O
[Ph(CH2)3Ph3P]Br
O
MeOH, rt, 6h, 96%
nBuLi, THF
0 0C, 0.5h, 90%
H
O
H2, 10%Pd/C
O
2
4
3
PPh3, DIAD
OH
OR
OH NO2C6H4CO2H
2M HCl, MeOH
OR
THF, rt
2h, 90%
rt, 1h, 97%
5
Na, MeOH
rt, 1h, 94%
R = NO2C6H4CO
6
OH
OH
OH
TsCl, (C2H5)3N
(nBu)2SnO, 0 0C-rt
7
TBDMS-Cl,
Imidazole
dry CH2Cl2
rt, 3h, 98%
OH
OTs
4h, 79%
8
OTPS
CN
DIBAL-H,
dry CH2Cl2
CN
KCN
Ethanol/H2O (3:2)
rt, 12h, 91%
SPTO
9
O
H
0
10
-78 C, 0.5h,
70%
11
Scheme 2
TBS protected aldehyde in compound 11 was reacted with ethyl diazoacetate and
tin chloride ( SnCl4) in the presence of dichloro methane at 0 0C to give the corresponding
β-keto ester 12. Deprotection of TPS group of compound 12 was done by treatment with
0.1 equivalent of PPTS in MeOH to afford compound 13 in 90% yield. In order to get syn
1,3-diol, compound `13 was subjected to syn-selective reduction using 2 equivalent of
catecholborane as reducing agent in dry THF at –10oC, which afforded the desired syn diol
II
Synopsis
14 in 95% yield. Protection of 1, 3 hydroxy groups of compound 14 was effected in dry
dichloro methane with 1.5 equivalent of 2, 2-DMP in the presence of catalytic amount of
pyridinium toluene 4-sulphonicacid for 3 h at room temperature to furnish 15 in 87% yield.
The cyclization of 15 was effected in dry DCM in the presence of a catalytic amount of
Para toluene-4-sulphonic acid for 6h at room temperature afforded final compound 1 in
84% yield (Scheme-3).
SPTO
OTPSO
O
H
O
ethyl diazoacetate, SnCl4
OEt
TBAF, MeOH
4Ao MS poeder, OoC-rt
11
OH
12
O
OH
O
OH
Catecholborane
O
OEt
OEt
2,2-DMP, PPTS
DCM, O0 C-rt
THF, -100 C
14
13
O
O
O
O
O
OEt
2,2-DMP, PPTS
DCM, O0 C-rt
OH
1
15
Scheme-3
SECTION-B: Total synthesis of Goniothalamin.
During the course of a program aimed at the synthesis of bioactive molecules, we
selected goniothalamin 16, a naturally occurring styryl lactone was isolated in 1967 from
the dried bark of Cryptocarya caloneura. Later it was isolated from Cryptocarya moschata,
Bryonopsis laciniosa and various species of Goniothalamus. Gonionthalamin 16 has shown
invitro cytotoxic effects especially by inducing apoptosis on different cancer cell lines
[cervical carcinoma (Hela), gastric carcinoma (HGC-27), breast carcinoma (MCF-7, T47D,
and MDA-MB-231), leukemia carcinoma (HL-60), and ovarian carcinoma (Caov-3)].
Goniothalamin 16 is a potent mosquito larvicide and also shows weak antibacterial and
III
Synopsis
significant antifungal activity against a wide range of gram positive and gram-negative
bacteria and fungi.
During the course of a program aimed at the synthesis of bioactive molecules, we
selected goniothalamin 16; an antitumor natural product was selected as our synthetic
target. Here we reported an efficient and stereoselective synthesis of goniothalamin 1 from
(R)-glycidol. Opening of epoxide with ethyl propiolate, cis hydrogenation and JuliaKociensky olefination are the key steps involved in our synthesis. The retro synthetic
approach for (R)-goniothalamin 16 may be represented as shown in Scheme 4.
O
O
O
OH
O
MPMO
OEt
O
HO
HO
O
16
20
18
17
Scheme 4
The synthesis of goniothalamin 16 is based on a sequence of reactions starting from
commercially available (R)-glycidol 17, which was protected with p-methoxy benzyl
bromide in presence of NaH in THF yielding the corresponding epoxy ether 18 in 95%
yield. 18.The opening of epoxy ether 18 with ethylpropiolate in presence of BuLi in THF at
–78 0C to produce the secondary alcohol 19 in 86% yield. The secondary alcohol 19 was
hydrogenated using Lindlar’s catalyst in the presence of hydrogen atmosphere in benzene
to the (Z)-α,β-unsaturated ester 20 in 91% yield.. Compound 20 was subjected to
lactonisation by treating the cis ester 20 in chloroform and using p-toluene sulfonic acid to
afford the compound 21 in 92% yield. The deprotection of MPM group in compound
21was proceeded smoothly with DDQ in dichloromethane/H2O (8:2) yielding the alcohol
22 in 92% yield.
The alcohol 22 was subjected to Swern oxidation to yield the unstable
aldehyde in 93% yield, which was directly used in Wittig reaction with benzyl triphenyl
phosphonium bromide in the presence of n-BuLi or KtObu provided 16 with the poor E/Z
IV
Synopsis
(1:4) selectivity. Attempts to employ the Julia-Kociensky protocol to selectively install the
desired E double bond configuration provided only goniothalmin 16 in 30% yield.
O
HO
NaH, THF, 0 0C-r.t.
O
MPMO
Ethyl propiolate, n-BuLi,
BF3.Et2O
3h, 95%
OH
MPMO
OEt
THF, -78 0C, 30 min. 90%
17
18
19
O
O
Pd/CaCO3, benzene
OH
MPMO
OEt
H2, 1h, 91%
PPTS, CHCl3
1h, r.t., 94%
20
O
O
DDQ
CH2Cl2/H2O (8:2)
MPMO
4h, 92%
O
O
21
O
(i) (COCl)2, CH2Cl2
DMSO, Et3N, -78 0C, 30 min
HO
(ii) then a solution of the 23,
KHMDS, THF, -78 0C (< 30%).
22
Ph
N N
N
N
S
O O
R1
O
R2
(R)-(Z)-(16), R1 = Ph and R2 = H
(R)-Goniothalamin (16), R1 = H and R2 = Ph
Ph
23
Scheme-5
CHAPTER-II
SECTION-A: The stereo selective synthesis of tiruchanduramine (24).
Synthesis of natural products is a challenging area. The total synthesis of natural products
involves prudent way of preparing and joining/stitching the various segments of the active
molecule using the different existing methods. Generally, the boundaries/targets are defined
by natural products, which at present is far reaching in spite of several advancements in
synthetic methodologies have been achieved. A novel -carboline guanidine alkaloid
tiruchanduramine 24 isolated from an ascidian Synoicum macroglossum, which was
collected at Tiruchandur, Tamilnadu, India during February 2002. Tiruchanduramine 24
showed promising α-glucosidase inhibitory activity (IC50 78.2 lµg/mL) as compared with
acarbose16 at 100 lµg/mL as the standard.
The plausible retro-synthetic analysis of the title compound is shown in the
Scheme-6, which recognized two conceivable segments 1) aromatic and 2) aliphatic part of
V
Synopsis
the molecule. The aromatic part of the molecule 3- carbolinic acid (29) can be readily
synthesized from the amino acid tryptophan(25).
H
N
O
N
N
H
NH
N
H
OH
O
N
H
N
H
N
H
N
OH
NH
+
H2N
NH2
40
24
O
O
O
HCHO
OR +
OH
+
NH2
N
H
N
H 25
Tryptophan
Scheme-6
O
H2N
N
37
R = H, OMe
29
Aromatic ring synthesis:
The 3--carbolinic acid (29) was prepared using Pictet-Spengler conditions.
Tryptophan 25 was reacted with aqueous formaldehyde in the presence of H2SO4 to give
tetrahydro 3--carbolinic acid (26) in 78% yield. Compound 26 was esterfied by bubbling
dry HCl gas in dry MeOH to give methyl ester 27 in 85% yield. Compound 27 was
aromatized using Pb(OAc)4 in acetic acid in the presence of oxalic acid to give 3-carboline methyl ester (28) in 56% yield. Compound 28 was further hydrolyzed with
NaOH in EtOH to give corresponding 3--carbolinic acid (29) in 90% yield (Scheme-6).
O
O
OH
NH2
N
H
31
Tryptophan
HCHO, H3O+
78%
O
OH MeOH, HCl
NH
N
H
85%
N
H
32
33
O
Pb (OAC)4
Ac OH, 56%
OMe
O
OMe
N
N
H
34
b-Carboline methyl ester
NaOH
OH
90%
N
H
35
Scheme-4
VI
N
b-Carbolinic Acid
N
Synopsis
1) Preparation of Aliphatic Fragment:
In order to prepare aliphatic part containing guanidine segment (37) of
tiruchanduramine, compound 37 was prepared starting from commercially available Lmalicacid (30). L-malicacid (30) was treated with methanol and catalytic amount of H2SO4
at reflux conditions for 12h to furnish the corresponding dimethyl ester (31) in 90% yield.
Reduction of this dimethyl ester with 1.2 equivalents of BH3.DMS and catalytic amount of
sodium borohydride in dry THF at room temparature for 3h afforded the corresponding diol
(32) in 80% yield. Protection of 1,2 hydroxy groups of compound 32 was effected in dry
DCM with 1.2equivalent of 2,2-dimethoxy propane (2,2-DMP) in the presence of catalytic
amount of p-toluene sulfonic acid (PTSA) for 3 h at room temperature to furnish 33 in 85%
yield. The ester group in 33 was reduced to alcohol 34 Using LiAlH4 at oC-rt in 90% yield.
The primary hydroxyl group in compound 34 as tosylated by using tosylchloride and
triethylamine in dichloromethane at room temperature to provide the tosylate 35 76% yield
Compound 35 s treated with 1.2 equivalents sodium azide in dry DMF to afford the azide
compound 36 in 80% yield. The azide compound 36 as hydrogenated by using 10% Pd/C
and NaHCO3 in ethyl acetate under hydrogen atmosphere at room temperature to afford the
acetonide protected amine compound 37 in 90% yield (scheme-7).
OH
O
HO
MeOH, Cat. H2SO4
OH
O
OH
OMe
O
O
PTSA
O
O
THF, 0 oC-rt, 3h
33
O
O
NaN3
OTs
35
DMF, 70 oC, 3h
THF, 0 oC-rt
OMe
32
O
OMe
O
HO
31
LiAiH4
O
OH
BH3.DMS
reflux, 90%
30
2,2-DMP, DCM
O
MeO
TsCl, (C2H5)3N
0 0C-rt, 4h, 85%
OH
34
O
O
O
N3
36
Scheme-7
VII
O
NH2
37
Synopsis
The amine 37 and 3--carbolinic acid (29) were coupled using DCC/DMAP in dry
DCM to give corresponding amide 38 in 70% yield. Also in a different experiment amine
37 and 3-carbolinic acid (29) were coupled using HOBT/EDCI to give amide 38 in 68%
yield. Acetinide protected amide compound (38) was reacted with BOC anhydride and
triethylamine in the presence of dichloromethane afforded the corresponding N-BOC
protected amide (39) in 85% yield. The deprotection of acetonide group in compound 39
was achieved by using pyridinium p-toluene sulfonate (PPTS) in dry methanol at room
temperature to afford the corresponding Boc protected diol 40 in 95% yield. Here PPTS
was working as a very mild catalyst, which does not deprotect the BOC and deprotects only
acetonide group.
A careful literature survey revealed that Murray Goodman et al reported new
guanidinylation reagents in the year of 1998. These reagents consist of N, N', N''-tri-Bocguanidine (a) and N, N', N''-tri-Cbz-guanidine (b), which allows a facile conversion of
alcohols to substituted guanidine’s. They synthesized a series of arginine analogues by
reacting of primary and secondary alcohols with guanidinylation reagents a and b under
Mitsunobu conditions. And reported N, N'-di-Boc-N''-trifylguanidine (c), and N, N'-di-CbzN''-trifylguanidine (d). The trifyldiurethane-protected guanidine c was utilized to
guanidinylate primary and secondary amines under mild conditions with high yield in
solution and on solid phase.
NBoc
BocHN
NCbz
NHBoc
CbzHN
NHCbz
a
b
NTf
NTf
BocHN
NHBoc
CbzHN
c
NHCbz
d
At this juncture again we went back to diol 40 and reacted with tri BOC guanidine
(a) under Mitsunobu conditions to afford the tetra Boc protected tiruchanduramine 41.The
VIII
Synopsis
Boc protected groups from the target molecule 41 was removed, which on treatment with
0.5 N HCl in dry methanol gave tiruchanduramine hydrochloride (24).
O
O
O
OH
37
N
H 29
N
O
HOBT+ EDCI
DIPEA, DMF
0 oC-rt, 6h
38
PPTS
MeOH, rt, 12h
OH
OH
TPP, DEAD, THF
N
H
Tri Boc Guanidine
40
Boc
N
O
N
Boc
N
N
Boc
39
N
Et3N, DCM
0 oC-rt, 2h
O
N
H
N
N
N
H
(BOC)2O
N
H
O
O
N
Boc
O
NH
N
H
N
Boc
H
N
O
TPP, DEAD, THF
Tri Boc Guanidine
41
Scheme-8
IX
N
N
H
24
NH
N
H
N
H
Synopsis
CHAPTER-II
SECTION-B: Chemical modification of polybrominated diphenylethers.
Br
OH
O
Br
Br
O
K2CO3, Acetone
Reflux, 6h
Br
OR
Br
Br
Br
Br
Scheme-1
R = Me
R = Ac
R = Allyl
R = - Allyl
R = (CH2)n-OH
n = 2, 3, 4, 5, 6
R = -CH(CH2)- COOEt
R = - CH2- Ph
R = CH2- CO-Ph
O
R=
-
H2C
Cl
X
Synopsis
Br
OH
O
Br
Br
Br
K2CO3, Acetone
O
1, 5-Dibromopentane
Br
Reflux, 4-5h
Br
Br
O
O
K2CO3, CH3CN
Br
Br
Reflux, 6h
Br
R
O
R
Br
Br
Br
R = Morpholine
R = N-methyl piperzine
R = N-Boc piperzine
R = Homo Boc piperzine
The above all the compounds showed antibacterial activity against gram positive and gramnegative bacteria.
CHAPTER III
XI
Synopsis
Synthetic organic chemistry has always been a frontier area of research due to its
impact on the material and biological sciences. The scientific community in this area is
constantly involved in developing efficient methodologies, novel reactions and processes
that will lead to the synthesis of desired target molecules and their derivatives with ease.
Synthetic organic chemistry is not only a tool for obtaining compounds that can be utilized
for understanding biological functions or the behavior of materials, but it also leads to the
creation of novel drug or drug like candidates and of novel materials with interesting
properties.
1) The chemo selective tetrahydropyranylation of primary alcohols using
La(NO3)3.6H2O as a catalyst:
The tetrahydropyranyl (THP) group is frequently used for the protection of alcohols
and phenols due to their ease of preparation and stability under a wide variety of reaction
conditions such as with hydrides, alkylating reagents, Griganard reagents and
organometallic reagents In addition, they also serve as stable protecting group in peptide,
nucleoside and nucleotide, carbohydrate and steroid chemistry. Tetrahydropyranylation is a
general and important protecting group to protect hydroxy groups in multistep organic
transformations. There are several reagents available for tetrahydropyranylation of
alcohols, which include the use of protic and Lewis acids. However several reported
methods are associated with certain drawbacks, which include long refluxing reaction time
conditions and the use for other functionalities. Thus there is a need for suitable, mild and
selective efficient alternative for the protection of hydroxyl functionality as THP ether. As a
part of our ongoing exploration of the acidic catalytic activity of lanthanum (III) nitrate
hexahydrate, we envisaged the chemo selective protection of primary alcohols with THP
ethers in the presence of secondary alcohols using La(NO3)3.6 H2O (Scheme-11).
HO
THPO
O
HO
BnO
O
O
La(NO3)3.6H2O
O
HO
O
DHP, rt, 2-3 h
BnO
Scheme 1
XII
O
Synopsis
Encouraged by the success of the reaction, various benzylic and allylic alcohols
were subjected to the tetrahydropyranylation with excellent yields. It has been observed
that the substrates containing other acid labile functional groups such as actinide, TBDMS,
isopropylidine protected diols were intact during tetrahydropyranylation . In order check
the versatility of the reagent La (NO3)3.6H2O, a mixture of 2-phenyl ethanol and 1-phenyl
ethanol were reacted with dihydropyran in the
presence of lanthanum (III) nitrate
hexahydrate to give exclusively THP protected 2-phenyl ethanol (Scheme-12).
OH
OH
OH
La(NO3)3.6H2O
+
OTHP
+
DHP, rt, 2-3 h
Scheme-2
In conclusion, we have developed a simple, efficient, mild, and highly selective
process for tetrahydropyranylation of alcohols using Lanthanum nitrate as a catalyst. The
mild, environmentally clean reaction conditions, and less reaction times with high yields
the advantages of the present methodology.
2) Acetylation of alcohols, phenols and amines with acetic anhydride using
La(NO3)3.6H2O as a catalyst:
Functional group protection strategies are central to target molecule synthesis. The
protection of alcohols, phenols and amines are fundamental and useful transformations in
organic synthesis. Among the many protecting groups for hydroxyls, phenols and amines,
acetate is used with high frequency. Although, numerous methods are available for the
preparation of acetates using acetic acid and a protic acid, acetic anhydride and pyridine are
the most commonly used reagents. 4-(Dimethylamino)pyridine (DMAP) and 4pyrrolidinopyridine (PPY) catalyze the acetylation of alcohols. However, most of these
reported methods suffer from one or more disadvantages like long reaction times, harsh
reaction conditions, the occurrence of side reactions, toxic reagents, poor yields of the
desired products and intolerance of other functional groups. Here, we report a mild and
XIII
Synopsis
efficient method for the acetylation of alcohols, phenols and amines using acetic anhydride
in the presence of La(NO3)36H2O (Scheme 13).
THPO
THPO
O
HO
BnO
O
O
La(NO3)3.6H2O
O
AcO
Ac2O, rt, 10-20 min
BnO
O
O
Scheme-1
We found that La(NO3)36H2O is an efficient and mild acidic catalyst for the acetylation of
alcohols with Ac2O under solvent-free conditions. In order to establish the catalytic activity of
La(NO3)36H2O, we carried out the acetylation of glucose diacetonide (1 mmol) with acetic
anhydride (1.2 mmol) using La(NO3)36H2O (5 mol %) at room temperature which gave the
corresponding acetate in 96% yield. Encouraged by the success of this reaction, various primary,
secondary, benzylic and allylic alcohols and phenols) and amines were subjected to acetylation in
excellent yields. Substrates containing other acid labile functional groups such as acetonide,
TBDMS and isopropylidene protected diols remained intact during acetylation. Interestingly, when
diols were subjected to acetylation, monoacetates were formed as the major products with very
good yields. From these results it is evident that acetic anhydride and lanthanum (III) nitrate
hexahydrate is an excellent combination for the acetylation of alcohols, phenols and amines under
solvent- free conditions. Thiols and thiophenols could not be acetylated using this method.
3) Synthesis of α-amino nitriles using Lanthanum (III) nitrate hexahydrate or Gadolinium
(III) chloride hexahydrate as a catalyst:
The addition of cyanide anion to imines (the Strecker reaction) provides one of the most
important and straight forward method for the synthesis of α-aminonitriles, which are useful
intermediates for the synthesis of aminoacids and nitrogen containing heterocycles such as
thiadiazoles and imidazoles, etc. The classical Strecker reaction usually carried out in aqueous
solution and the work-up procedure is also tedious. Thus several modifications of Strecker reaction
have been reported using a variety of cyanide reagents, such as diethyl phosphorocyanidate and α-
XIV
Synopsis
aminonitriles, as well as catalysts, such as InCl3, BiCl3, Montmorillonite KSF clay, Sc(OTf)3,
Bromodimethyl sulfonium bromide under various reaction conditions. The use of trimethylsilyl
cyanide is a safer and more effective cyanide anion source for the nucleophillic addition reactions
of imines under mild conditions. However, many of these methods involve the use of expensive
reagents, harsh conditions, extended reaction times, and also require tedious work-up leading to the
generation of a large amount of toxic waste. Further more many of these catalysts are deactivated
or sometimes decomposed by amines and water that exist during imine formation. In order to
overcome these problems recently one-pot procedures have been developed for this transformation.
In continuation of our work to develop new organic transformations, here we report that a mild
efficient and environmentally benign catalysts, for the preparation of α-aminonitriles from
carbonyl compounds, amines and trimethylsilyl cyanide in presence of La(NO3)3.6H2O or
GdCl3.6H2O in acetonitrile at room temperature (Scheme 14).
R-CHO + R'-NH2 + Me3SiCN
1
2
La(NO3)3.6H2O
or
GdCl3.6H2O
MeCN, r.t.
1.0 - 3.0 h
3
NHR'
R
CN
70 -98%
4
Scheme-1
In conclusion that the present procedure using Lanthanum(III) nitrate hexahydrate or
Gadolinium(III) chloride hexahydrate provides an efficient synthesis of α-aminonitriles by a onepot three component coupling of carbonyl compound, amine and TMSCN. The salient features of
this methodology are: General applicability to different types of aldehydes and amines, using cheap
and commercially available reagents, short reaction times, and high yields of products. Finally this
report provides us towards environmentally-friendly chemical processes.
4) Synthesis of homoallylic alcohols using Lanthanum (III) nitrate hexahydrate as a catalyst:
The Lewis acid catalyzed addition of allylstananes to aldehydes for the preparation
of homoallylic alcohols is important organic tranceformation as they are important building
XV
Synopsis
blocks and versatile intermediates for the synthesis of natural products . This has led to
development of new synthetic methodologies for the synthesis of homoallylic alcohols.
Organic reactions using mild and water tolerant catalyst have been received much
attention in recent years as they can conveniently be handled and removed from the
reaction mixture, making the experimental procedure simple and eco-friendly. In the course
of study in above transformations.
O
R
H
+
OH
La(NO3)3.6H2O
SnU3B
CH3CN, r.t
R
Scheme-1
In this report we have described an efficient method for the synthesis of homoallylic
alcohols using mild Lewis acid catalyst. The reaction proceeds efficiently and smoothly at
room temperature and the products are obtained in excellent yields. Furthermore, the
reaction conditions are very mild, no by-products were observed. Initially, we have reacted
allyltribultylstannane with benzaldehyde in acetonitrile at room temperature using catalytic
amount of lanthanum (III) nitrate hexahydrate (5 mol%) to give corresponding homoallylic
alcohol in 99% . In order to check the veracity of the catalyst we paid attention to other
substituted aromatic aldehydes, ,-unsaturated and aliphatic aldehydes to give
corresponding homoallylic alcohols. In all the cases the obtained yields are good to
excellent. The chiral substrates containing acid labile protective group such as acetonideprotected diols were also converted into corresponding products without disturbance of
chirality as well as acetonide. In conclusion we described mild and an efficient synthesis of
homoallylic alcohols by the reaction of aldehydes with allyltribultylstannane using catalytic
amount of La(NO3)3.6H2O. The present method has the advantage of mild reaction
conditions, comparatively less reaction time and improved yields of the products. We
thought that it is an important addition of existing methodologies.
XVI