Pergamon

0040-4039(95)01784-4

Tmahedron Lprters. Vol. 36, No. 46. pp 8513.8516. 1995 Elsevter Science Ltd

Pnnted in Great Britain 0040.4039/95 $9.50+0.00

1-(Benzoylamiao)-3-methylimidazolium Chlomchmmate (BAMICC), a New Selective and

Mild Reagent for the Oxidation of Allylic and Benzylic Alcohols

Yolanda Martinez, Maria A. de las Heras, Juan J. Vaquem, Jo@ L. Garcia-Navio and Julio Alvarez-Builla”

!kpartament~~ dr @mm Orpmca. I’n~vrrsldad de hlcali 2X871 -.Alcala de lienares, Madnd Spain

Prior to 1975 the prtnctpal oxochromtum-amtne reagent used for the converston of alcohols to carbonyl

compounds was the C’ollms reagent’ and related systems based on the chromtum trtoxtde-pyrtdme complex

first descrrbed by Sarett ’ Stnce the rntroductton by Corey and Suggs of the pyrtdmium chlorochromate (PCC)3,

complexes of chlorochromate w-tth ltgands such as 2,2 -brpyrtdme,” 4-(dtmethylamtno)pyrtdme,5 1,8-

naphthyrtdme,” pyrazme”” and trtalkylammesX rn/er alra have been reported In general, these amme-

chlorochromate complexes are molder than the actd-based reagent systems and show vartous degrees of

selecttvtty towards the oxtdatton of alcohols to carbonyl compounds dependmg on the donor strength of the

assoctated amme ltgand ‘a’9 However. m most cases oxtdation stall rematns difficult on substrates contaming

baste nttrogens, smce exchange may occur with the oxtdant to gave substrate-chromrum complexes.”

Fyidine (FCC) BppMe (WCC) qmytamino)~idi (uvt4Fcc) 1 ,ENapMhyMine (NapCC) R/raam mm

BPMICC

Scheme I

Our Interest m new synthettc appllcattons of 1-(acylammo)cyclotmmonium salts”“’ led us to explore the

preparatton and oxtdant properttes of chlorochromate salts whtch mcorporate an N-amtmde as a hgand for the

ftrst ttme and here we report our unttal results tn the use of I-(benzoylammo)-3-methyhmtdazolrum

chlorochromate (BAMICC) as a new chromtum(V1) complex oxtdant

Of the vartous N-ammtdes explored. a combmatton of I-methyltmtdazole as heterocycle and the benzoyl

group as acyl motety gave a nonhygroscoptc and atr-stable chlorochromate salt which was easily prepared from

8514

the N-ammrde 2 and CrO, m the presence of HCI Like other complexes, BAMICC does not dtssolve

apprecrably m orgamc solvents. The selectrvtty of thus reagent was mdtcated by the absence of oxrdatron of

prrmary and secondary alcohols when compared to the slow oxrdatron of allylic or benzylic alcohols. Thus

treatment of 2-phenylethanol or 2-cyclohexylpropanol (see Table, entrres 1 and 2) m refluxmg CH,CI, with

5 0 equrv of BAMICC for 48 h leads to recover unchanged the alcohols Thus result contrasts with those

obtamed wrth benzylrc alcohols (entrtes 3-S) whrch are oxrdrzed m CH,Cl, to the corresponding aldehydes or

ketone usmg I 5 equrv of the complex. When a hrgher excess of the oxrdant was employed a reaction rate

enhancement was observed w-rthm the first two hours but the reaction was completed only after 15 h at reflux

temperature (entry 3) Under srmrlar conditions allylrc alcohols are also oxrdized to the correspondmg a,P-

unsaturated aldehydes rn good yields although the oxrdatron of Z-2-hexenol resulted in extensrve geometric

rsomerrzatron of the double bond either usmg I 5 or 5 equrv of the reagent (entry 6)

1 K2C03 i CH2Cl2 2 HCl/Crq

MSH = 2.4.6.tnmethylixnaresulfo~ hydraade

R 01 R’ = Ar, RCH=CH

Scheme 2

$4 remarkable utrltty of BAMICC was found m the oxrdatron of substrates bearing basic nitrogens (entries

7-9) Substrates such as 2- or 3-pyrrdylcarbmol proved to be more reactive than benzyl alcohol and complete

conversron to the correspondmg aldehydes were obtamed usmg I 5 equrv after 8 h. Under srmrlar conditions

other prevrously reported chromrum(V1) complexes farled to give this conversron due to above mentioned

exchange problems ”

Two drols were also tested for rllustratmg the selectrvrty of this reagent. The oxrdatron of 1-phenyl-1,3-

propanedrol (entry 10) wrth 1 S equrv afforded the ketone In 75% yreld, whereas the phenylglyoxal was the

mam reactron product (58%) obtained when the 1 -phenyl- I ,2-ethanedrol (entry 11) was subJected to oxrdatron.

In the latter case the mrtral formatron of the ketone presumably actrvates the remainmg primary alcohol group.

It should be noted that a further advantage of this reagent IS that at the end of the oxrdatron process the

rmrdazolrum salt 3 produced can be easrly recovered and reused to obtain the BAMICC complex through the

N-amnude 2 (Scheme 2)

8515

Table. Oxidation of Abhols to Carbonyl Compounds with BAMKK;:

ENTRY ALCOHOL CARBONYL CONDITIONS YIELD?6 coMPouNLl Equiv Tii (h) cx-&l,

1 0”

OH 1:

OH

2 CY-

3 0” ‘I OH \

a-

5 0% :I :I

6

7

8

9

10

w”

c.k ’ I \ ok N

CJ- ‘I OH \ N

Me

/ /

@CL \ \ OH

N

ai

OH

OH

11

e

OH

1:

10

10

1.5

1.5

5

1.5

1.5

1.5

1.5

1.5

5

1.5

1.5

1.5

1.5

1.5

1.5

48

48

8

20

15

25

2

2

20

2

15

25

8

8

8

20

20

r. t.

r. t.

reflux

reflux

reflux

0

0

35

83

83

92

33

71

82

46

81 ~/2(3:1)

80 E/z(3:1)

81

83

a3

79

56

8516

The BAMICC reagentI was prepared as follows. To a stlrred solution of CrO, (1 g, IO mmol) m 6N HCI

(10 ml), a solution of the N-ammlde 2’l (2 g, 10 mmol) m 20 ml of 6N HCl was slowly added The reaction

mixture was cooled to 0 “C and the yellow-orange solid formed was collected by filtration, washed with water

and dried under vacua (yield 3.1 g, 92%). In a typIcal oxidation procedure the reagent was suspended m

CH,CI, (5 ml for each 0.5 mmol) and the alcohol (0 5 mmol) was added. The mixture was refluxed until the

alcohol was consumed (see table) and then diluted with dry ether (10 ml). The supernatant was decanted and

the insoluble residue washed with dry ether (3x5 ml) The combmed organic solution was passed trough a short

column of cehte, and the solvent was removed under reduced pressure. The carbonyl compound was purified

by dlstlllatlon or column chromatography The N-amnude 2 was recovered by treatment of the insoluble

residue with K&O, (0 55 g, 4 mmol) m CH,CI, (15 ml) After stirring for 4 h, the orgamc phase was separed

by filtration and 2 was isolated m a 83% yield by simple removal of the solvent

In summary, the use of BAMICC IS a cheaper and cleaner alternative to other chromlum(VI) complexes

for the oxldatlon of allyhc and benzyllc alcohols. lncludmg those bearing basic mtrogens. Further studies of

the oxidant propertles of this and related reagents are In progress In our laboratory and WIII be reported on due

course

Acknowledgements The authors are grateful for a grant (MAH) received from Mlmsterio de Educaci6n

y Clencia and for fmanclal support from Comlsi6n lntermmisterlal de Clencia y Tecnologia (CICYT, proJect

PB90-0284)

REFERENCES AND NOTES

1 Collms, J C Hess, W W , Frank, F J 1crraheJron I,eft. 1968, 3363.

2 Poos, G I , .Arth. G E Beyler, R E , Sarett. L H J Am (Them. Sot 1953, 75, 422.

3 (a) Corey, E., Suggs, J W I’etruhedron Letf 1975. 2647 (b) For a review of PCC see: Plancatelll, G.

Scettrl. A , D’Aurla, M Synthesrs, 1982, 245

4. Guzlec, F S . LUZZIO. F A Syntheszs, 1980. 691

5 Guzlec, F S , LUZZIO. F A .I 0rg (‘henr. 1982. 47. 1787

6 Davis, H B., Sheets, R M , Brannfors. J M Paudler. W W.. Card, G. L Heferocycles, 1983, 20, 2029.

7 (a) Davis. H. B _ Sheets. R M., Paudler. W W . Card, G L., Heterocycles, 1984, 22, 2029. (b) Doad,

G, J S .I (‘hem &es. (S), 1988. 270

8. (a) Rao, C G Radhakrlsna, A S , Slngh. B B . Bhatnagar, S P Synthesis, 1980, 808. (b) Santaruello,

E , Mllanl. F Casatl. R Synthesis. 1983. 749 (c) Acharya, S P , Rane, R. A Synthesis, 1990, 127.

9 Guerrero. A F . Kim, IH J , Schlecht, M F I’erruhedron Letf 1988, 29, 6707

IO (a) Ley. S V , Madln. A Oxldatlon Adjacent to Oxlgen of Alcohols by Chromlun Reagents in

(‘omprehensrve Oqanrc Syn/hesls, Trost. B , Fleming, 1 Eds vol. 7. p 25 I-289, Pergamon Press, Oxford,

1991 (b) LUZZIO, F A.. Guzlec. F S Org Prep Proced. Int 1988. 20, 535

11 Heras, M A Mollna. A. Vaquero, J J , Garcia-Navlo, J L , Alvarez-Bullla, J J Org. (‘hem , 1993, 58,

5862

12 Heras, M A . Vaquero, J J Garcia-Navlo. J L i\lvarez-Bullla, J. l’etruhedron Left 1995, 3, 455.

13 BAMICC yellow-orange powder. mp 113-114 “C, IR (KBr) v,,,3103, 2954, 1634, 1514, 1273 cm-‘.

‘H NMR (300 MHz. D.MSO-d,) 6 12 80 (bs. 1H). 9 46 (s. IH). 7 9 (m, 3H). 7 77 (bs. lH), 7 6-7.5 (m,

3H). 3 91 (s. 3H) ppm

(Received in UK 28 July 1995: revised 19 September 1995; accepted 22 September 1995)