Indian Journal of Chemistry Vol. 408. July 200 I . pp. 550-557

Advances in Contemporary Research

InCl3 in organic syntheses

Rina Ghosh Department of Chemistry, Jadavpur University, Calcutta 700 032, India

A revi ew on the use of InCl3 in organic syntheses is described.

Introduction Lewis ac id catalysed carbon-carbon bond forming

reactions have fo und widespread applications in organic synthesis Jo

•b

. The attracti ve fea tures of these reactions are their mild reaction conditions, improved stereo- and chemoselecti viti es and the prospec t of catalytic asymmetric induction via use of chirally modified Lewis ac id catalysts. Although several Lewis ac ids, based on main group and transition metal sa lts, have already been used for these purposes, newer Lewis ac ids are being regul arly scanned in search of improved efficiencies. In recent years, InCl3

has evolved as a versatile Lewis acid catalyst for a variety of organic transformations, e.g., aldol condensation, Diels-Alder reactions, Michael additions, glycosy lation reacti ons, etc. Compared to the conventional Lewis ac ids, a number of advantages have already been noted for InCl3 viz., low catalyst loading, moisture compatibility and catalyst recycling, whi ch promises broader rami ficati ons in years to come. The purpose of thi s review is to hi ghlight these and other interesting fea tures of InCl3 as applied to organic synthesis2

.

Nucleophilic addition to carbonyl compounds

(i) Mukaiyama-aldol reactions: Since the di s­covery of Mukaiyama-aldol reaction3a a wide variety of Lewis acids have been ex plored3b

.g for this

reaction. In fact, Mukaiyama and coworkers4 were the first to successfully utilise InCl 3 as a catalyst for aldol reactions in organic solvents (Scheme I). They showed that while aldehydes and acetals reacted with trimethyl or triethylsilyl enol ethers, only the former underwent reaction with the sterically more hindered silyl enol ethers.

Subsequently, Loh and coworkers5 described a highly improved InClr catalysed Mukaiyama-aldol reaction in aqueous solutions. The procedure which

R'CHO ''.l RlSICI + InCI3 ''.l ~ID4 yiD4

(10 mol%) + R R4 -----.. R 4 R1 or

Solvent R2CH(OMe)2

or

Scheme I

InCI3 (20 mol%) ..

R'CHO, 230 , H20, 15h

Scheme II

R'V:' R4

M R"

85-97%

owes its success to the unique hydrolyti c stability of InCb, however, is highly dependent on the order of addition of the reagents. Best resul ts were obtained when the silyl enol ether was added to a mi xture of the aldehyde and InCl3 followed by water6

(Scheme II). High yields in InCl3 catalysed aldol reactions have also been reported in sol vent free conditions or under micell ar systems 7. The catalytic ability of the reagent was compared8 wi th that of other metal salts in aqueous medium using the model Mukaiyama- aldol reaction of benzaldehyde with (Z)­I-phenyl- l -(trimethylsiloxy) propane. An InCl3

induced highly stereoselective Mukaiyama-aldol reaction has been applied for chain elongation of a glucose derived silyl enol ether9

•

(ii) Prins type reactions: Lewis ac id catalysed Prins reactions JOa-e between aliphatic aldehydes and alkoxyallylsilanes usually produce the respective tetrahydropyran derivatives in good yields; aromatic aldehydes are usually unreactive JOb-d . In contrast, Li et. al. J ta-c have shown that InCl3 mediated Prins reaction of both aliphatic and aromatic aldehydes with

GHOSH: InCI) IN ORGANIC SYNTHESES 551

homoally lalcohols led to the corresponding tetra­hydropyran derivatives in excellent yields with high diastereoselectivity.

Recently, we have successfully carried out the Prins reactions of benzaldehydes, 11I-chloro- and /1/­

bromo benzaldehyde with allyltrimethy lsi lane lead ing to the respective pyran derivatives in moderate to good yields t .

(iii) Carbon-carbon bond formation via trans­metallation of organometallic compounds with InCh: In situ generation of organoindium reagents via transmetallation between conventi onal organo­metallics and InCI 3 has found considerable use in organic synthesis. An allylind ium species generated via transmetallation of ally lmagnesium bromide with InCI3 was used by Whitesides et. ai l 2

• for diastereo­selective add it ion to free aldoses leading to higher sugars. Similar in sitll generated y-alkoxyall ylindium reagents and their add ition reactions to aldehydes has also been reported by Hirasita et. ai.13

• Triorgano­indium reagents derived from organolithium compounds and InCI 3 have been used for I A-addit ion reactions to enones in the presence of nickel catalysts 14 (Scheme III).

InCI3 mediated transmetallation of a-a lkoxyally l stannanes for carbon-carbon bond formation in reaction with different aldehydes including sugar based aldehydes, leading to the con'esponding coupling products in high yields and anti selectivity, was first demonstrated by Marshall et.ai. IS

.16 (Scheme

IV). The observed stereospeci fic and diastereo­selective SEi addition to aldehydes generating the major anti adducts, have been rationalised l6 by involvi ng a transient organoindium intermediate (AlA'). Ethyl acetate has been found to be the solvent of choice for this exchange and coupling reaction le~.di n g to higher yield and diastereoselectivity of the products with the exclusion of the y-adduct I6

.

A number of InCI3 catalysed addition reactions of allyl tin compounds to aldehydes I7

.22

, trifluoroacet­aldehyde hydrate and hemiacetal23

, and ketones l9,

have been reported . Nishigaichi and coworkers2 1

studied the reactions of a-oxygenated aldehydes (la-c) and tributylpentadienyltin 2 in the presence of various Lewis acids (Scheme V) and fou nd that InCI3

catalysed reactions with benzyl protected aldehydes produced practically one isomer- the syn y-adduct 4. Among the solvents examined , acetonitrile was found

tour unpublished resu lts

InCI3 3RlI -THF

RCHO

+ SnBu3

M~OP (R-IS-)

6 » R OH

RJln ~ + I N'CoI. TNF 0

13-80%

Scheme III

InCI3, McCN

OH

M~ . R

OP anti

.. ' OH

~ ~ R OP

anti InCI3, EtOAc OH

M~ : R

OH

~R Me

y-adduct

M~Me i Me

OP y- adduct

OH ¥R OP syn

".[ ~p/ (A)

OP ~ 1 anti (major)

Me 01 (A')

Scheme IV

OP

;:

InGI3 • .1 A. /A // + ~snBu3-R" I V'/'V

HO 2 OH 1a-c syn3

~ R :

OH anti 3

&-adduct

~ OH syn4

~ R :

OH anti 4

y- adduct

Scheme V

LO give the best result with respect to yield, rcgio- and stereoselecti vity and the rate of the reaction. The reacting species was supposed to be an in situ generated dichloropentadienylind ium 2a which reacted via chelation controlled SIX membered transition state (B) (Scheme VI).

Yasuda and coworkers24 have investigated the alkyny lation of aldehydes with alkynylindium species generated via transmetallation from alky nyltins and InCI3 in the presence of chlorotrimethylsilane (Scheme VII). Formation of the product C from the

552 INDIAN J CHEM. SEC. B. JULY 200 I

pP 1:1 OP

~lnCl2 AHO[ A.. R~~:!rC'2Ior - ~/"C'21 2a - // ~" H"'k\d

f - (B! - OP "R (B')

2

chelation . InCI3 model non~helatlon

model

1

~ lc OH

syn 4

Scheme VI

y- adduct

OH anti 4

...JnC13 (10mol%) R'

r-R OSiMe3

BU3Sn = R + R'CHO + Me3S1 OCi -M-ee-N-"

64-100% Scheme VII

add ition of alkynyltributyltin A to aldehyde B in the presence of chl orotrimethyl silane has been assumed to follow a catalytic cycle as illustrated in Scheme VIII.

InCI) catalysed transmetallation of the organotin compound 5 followed by an intramolecular cyclisation reaction has been reported to produce the cis-cis cyclic compound (7) with high stereo­selectivit/5 (Scheme IX).

(iv) Miscellaneous reactions: InCI3 catalysed addition of allyl-, ary l- , vinyl- , ethyny l- and propargyl silanes to chloral and chloroacetone26 and of al lyltrimethylsil ane to acy l chlorides27 has been reported. InCI3-AgCI04 mixture has been shown to be an effecti ve catalyst system for addition reactions of various silyl nucl eophiles28 to aldehydes. Loh et.al. has reported an InCI) catalysed aqueous one-pot Mannich type reacti on of aldehydes, amines and silyl enol ethers affordin g B-amino ketones and esters in moderate to good yie lds29. Sengupta et.al.3o utilised InCI) in the addition reaction of diazocarbonyl compounds to aldehydes and ketones. An efficient synthetic route to a -amino phosphonates has been developed by Ranu et.al. 31 via an InCI3 catalysed one­pot reaction between aldehydes or ketones and amines with diethylphosphite. They have also used this catalyst on Si02 support for the preparation of quinolines from ani lines and alkyl viny l ketones32.

(C) MerRt,R

Me3SICI ,nCr'3 R - SnBu3 (A) yR

~nC12 BU3SnCI

~R=I",," R'CHe

(B)

Scheme VIII

OH OH

a=</vvvsnBu3 ~ ~ ... >Z:. / + ~ / o=(" 5 DCM ~J 1 V 1

6 7

Scheme IX

Michael reactions L . . did M ' hi' 33·,· h f eWls aC I cata yse ' IC ae reactions' " are 0

considerable current interest in view of their non­basic and mild reaction conditions. InCl .l catalysed Michael reaction of silyl enol ethers to a,B­un saturated carbonyl compounds has recently been reported34 (Scheme X).

Again, due to the excepti onal hydrolytic stability of InCi3, Michael addi tion of primary and secondary amines to acrylates, crotonates, acryloni triles etc. can be carried out in water in moderate to good yields with InCI3 as the catalyst35 (Scheme XI).

Diels-Alder reactions Diels-Alder reaction is amongst the most widely

used carbon-carbon bond forming methods in organic synthesis36a.c. A variety of Lewis ac id catalysts, in both organic and aqueous media and under different conditions of temperature and pressure have been investigated for Diels-Alder reactions36b

.c

. InCI, catalysed aqueous Diels-Alder reaction has been shown to proceed37

.".b in good to excel lent yields with high endo/exo selectivity. The catalysts in these reactions could be recovered and recycled without loss in activit/7a (Scheme XII) . Ab initio calculations have establi shed a three-centre orbital interaction for the model Diels-A lder reaction of butadiene and acrolei n catalysed by InCI3 as well as for · few other metal chlorides38.

GHOSH: 1110.1 IN ORGA Ie SYNTHESES 553

o OTMS

~' R"' I R' "V'.

R'" InGll (20mol%) i i K

neat • RV V' 1" "R R

12.aS% anli product predominant

Scheme X

Scheme XI

A A H2O A + X -InCI3 n-O,1,2 X=EWG

Y=H/OP 81-99%

Scheme XII

Imino Diels-A lder reactions of Schiff's bases with • :I<J 40 :I I) cyclopentad lene" and cyc lohept-2-enone' have

been carried ou t with 20% anhydrous InCI} as (he catalyst to produce cyc lopentaquinoline and azabi­cyclanone deri vat ives in good yields (Scheme XIII). InC I) catalysed one-pot imine formation-imino Diels­Alder reaction has also been carried out with cyclopentadienes and 3,4-dihydro-2H-pyran affording new quinoline derivatives in good yields4la. Thc method has also been used for the sy nthesis of pyranoquinoli nes, indenoquinolines and phenan­thridine derivat ives4lb. A si milar sequence has been reported for the Diels-A lder reaction of ill sill! generated heteroaromatic imines with cyclopenta­diene4l c. A stereo- and regioselective sy nthesis of cis­pyrroloquinolines has been carried out by InCI) induced imino Diels-Alder reaction of aniline derived imines and cyclic enamides42 .

Friedel-Crans reactions (i) Acylation: While in Friedel-Crafts acylation

reactions a stoichi ometri c amount of Lewis acid is genera lly required4Ja.c. in case of activated molecules the reaction may proceed with catalytic amou nts of Lewis ac ids44a.d . InCIJ-AgCl04 combination has been reported to be an effecti ve mcdiator for Friedel-Crafts acylat ion of anisol e in good yiclds.J5. Art el.al .46

successfu lly effected thc acylat ion of 2-mcthoxy­naphthalene with acid chlorides using catalytic

R1

20 mol% InCI3 ~H 0 • R2

MeCN, r.t. H

H Ar 58-95%

j Ar' 6 ~~/:AN/r' I + I Ar ?"

17 Ar H major Ar

overall 62-74%

l: 6 ~ R,{ A/" ArH ~ Ar

mixed selectivity overall 48-78%

Scheme XIII

InCI3 (5 mol%) + ArH (X's) + Me2SiCIH •

Scheme XIV

R1

)-Ar

R2

42-99%

amounts of various Lewis acids and have shown that 2-acyl-6-methoxynaphthalene could be produced predominantly over l -acy l-7-methoxynaphthalene by using InCI} as the catalyst.

(ii) Reductive Friedel-Crafts reaction: Alkylation of aromatic systems with carbonyl compounds via

Reductive Friedel-Crafts reaction, is a potentially use ful synthetic methodology. Ga2C1447a.b, Sc(OTf)/ 8a.h and trinuoromethanesulfonic acid49 have

been used as the catalysts for these reactions. Recently. Miyai and coworkers50a.b have reported the Reductive Friedel-Crafts alkylation of aromatic compounds with aldehydes and ketones in the presence of catalytic amounts of InCI) and chlorodi­methy lsi lane as the hydride source (Scheme XIV).

A plausible mechani sm for thi s reaction has been proposed involving (i) hydros ilylation of the carbonyl component. (i i) genera tion of a carbocation by desiloxylation and (i ii) alkylation of the aromati c substrate, a depicted in Scheme XV. Both hydro­silylation and alkylation steps were shown to proceed on ly in the presence of InCIJ.

554 INDIAN J CIIEM. SEc.n, JULY 200 1

InCI3 --(i)

R1

rOSiCIMe2

R2 I (ii) .lnCl3

~ ~+ (iii) /

R2

Scheme XV

Glycosylation reactions Due to the manyfold biological utilities of

ol igosaccharides, glycoconjugates5la-e and C-glycosyl compounds52a-d, glycosy lation reactions (0_5Ia-c and C_53H

) are of much current interests. Recen tly, we have used InCl3 as a mediator for C­

glycosylation reaction of peracetylglycals with allyltrimethylsilane54 . Thi s C-glycosylation reaction proceeded in good yields and with high aI/Ii diastereo­selectiv ity (I, 5-al/li diastereoselectivity with pera­cetylated hexopyranoglycals and 1,4-al/li-diastereo­

selecti vity with peracetylpentopyranoglycal ) (Scheme XVI).

The InCl r AgCI04 system has been shown to be quite useful for O-olycosylation of benzyl protected

b ~ glycosyl acetates55 . Babu and Balasubramanian have reported an efficient syn thesis of 2,3-u nsaturated glycopyranosides via InCI) catalysed Ferrier reactions of tri-O-acetyl-D-glucal with a number of alcohols and phenols.

Miscellaneous reactions In addition to the aforementioned examples, there

are number of addi tiona l applications of InCI) in organic synthesis. Recently, Sengupta el.al. 30 has successfully used InCI) as a catalyst for some reactions with diazocarbonyl compounds viz., SoH insertion reactions, nitrile cyclisations and addition reactions to aldehydes and ketones (Scheme XVII). InCI] catalysed reactions of diazoacetates with imines have also been reported by the same au thors to produce cis-aziridine carboxylates with high diastereoselecti viti7

.

InCI} catalysed rearrangement of aryl subst ituted epoxides leads to substituted benzylic aldehydes and ketones58 (Scheme XVIII) . Alkyl substituted epoxides also undergo simi lar rearrangement but with lower selectivity. The reaction tolerates several functionalities such as -OMe, -C02Me, -C=C-, -C=C­elc.

.,)1 D~c

InCI3, ~SiM .. e3 R'y~

CH2CI2, r.t. ~

Ac 70-100%, dr>9:1

Scheme XVI

PhSH ~ SPh /".../ (80-95%)

~R' LL~ 50%

R'CHO ~R(15.a1%)

Scheme XVII

R~R2 T~t. )(:R2

A~ R3 InCI3 Ar ~ 50-95%

R1,R2,R3 = H/alkyl/phenyl

Scheme XVIII

Dichloroindium hydride generated ill silu via transmetallation of tribu tyltinhydride with InCl3 has been used for reductions of aldehydes, ketones and bromo compounds59. With a,~-unsaturated systems this reagent led to regioselective lA-reduction of the double bonds. Indium hydride generated from BU3S nH and InCI) in the presence of added phosphines has been reported to reduce acid chlorides to the respective aldehydes60

• Hydrodechlorination of I, I ,2-trinuoroethane over Bi-Pd, supported on metal ox ides in the presence of InCI3, proceeded in high yield to produce trinuoromethane6 1

• Reductive deoxy­genation of arylketones and secondary benzylic alcohols have been reported using the InCl)" Me2SiCIH combination, where functionalities as halogen, ester and ethers were tolerated during the reduction62

. InCl) has also been used in the splitting of ether by chlorotrimethy lsi lane and in the reaction of trialkylhydrosilane with ketones63

.

InCl3 has been reportedly used for chlorination of chlorophenylsi lane64 and pyridineb5 and for bromi­nation of quinoline66

. A bimetallic system (AI -InCI)) has been found to be effective for allylation of imines derived from methyl vallinate67 and that of enamine68

.

InCl3 has been used as a versatile catalyst for

GHOSH: InCl., IN ORGANIC SYNTHESES 555

polymerisation reactions6?a-

p. It has also been used as

an efficient med iator for various other reactions as mentioned in patent abstract70-76.

The utility of InCI3 in combination with other catalysts for the following reactions are also worth mentioning. InClr TMSCI combination has becn shown by Mukaiyama and eoworkers77a.b to eatalyse the reaction of O-trimethylsilylmonothioacclal s, trimethylsilane and silylalcd carbon nucleophilcs leading to sulphide dcrivatives. The aUlhors have modified77b the method for one pot sy nlhcsis of sulphides in hi gh yic ld from aldchydcs, trimelhylsil ylalkyl or aryJsulphide and lrialkylsilane using lhi s catalys t system. Synlhesis of carboxyli c e. tel' or S-phenylcarbothi oalcs were achi evcd l'i(l anhydride based esteri fical ion usi ng I nCI 3-AgCIO-l catalyst system78. Reports have al so bccn Illacle on hydrolysi s of phosphale eSler7? using InCl .l as a co­operative catalyst wilh La(III).

Although it is nol possible 10 include the references of the increasing use of olhcr indium halides, il Illay be mentioned that InF3~(), Inl 381 a.b, In1 82, as well as In (OTfh 83a-c ele. have also found important applica­tions in organic synthes is.

Conclusions InCI3 has emerged as an effective mediator for

various organic transformation s. The advantages of thi s catalyst are its low toxicity and hydrolylic stability. Due to the latter, many reactions wilh InCI3 can be performed effeclively in water2-7.9. 18.25.35 . .l7a under environmentally bcnign conditions8-l. Moreovcr, InCI3 can be recovered and recycled without appreciable loss in its reactivit/7a . InCl3 has lhus acquired a special importance in contcmporary organic synthesis and has considerable potcnlial for further exploration particularly in developing large scale synthetic products in aqueous media.

Acknowledgement Financial assislance from CSIR (Schcme No.

o 11I463/97/EMR-II) and DSA-UGC (New Delhi ) is gralefully acknowledged.

Addendum Since the submission of this manuscript following

reports on various uses of InCI" in organic synlhesis have appeared : Ranu n C, Ellr J Org ClICIII, 2000 , 2347; Chauhan K K & Frost C G, J C/iC/1I Soc Pakill TrailS I, 2000, 3015; Loh T -P, Liung S I3 K W, Tan K -L & Wei L-L, Tetra/icdron , 56, 2000, 3227;

Kobayashi S, Busujima T & Nagayama S, C/ielll A ElIr J, 6, 2000, 3491; Yasuda M, Onishi Y, Ho T & Baba A, Tetrahedroll Lett, 41, 2000, 2425; Hirashita T, Kinoshita K, Yamamura H, Kawai M & Araki S, J Chelll Soc Perkin Trans I, 2000, 825.

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