Sodium perborate: A mild and convenient reagent for efficiently oxidizing trialkylboranes

Tetrahedron Letters,Vol.30,No.l2,pp Printed in Great Eritain

SODIUM

PERBORATE:

A MILD

1483-1486,1989

AND

OXIDIZING

George W. Kabalka’,

CONVENIENT

REAGENT

FOR

+ .oo

EFFICIENTLY

TRIALKYLBORANES

Timothy

Departments University

0040.-4039/89 $3.00 Pergamon Press plc

M. Shoup, and Naganna M. Goudgaon

of Chemistry

of Tennessee,

and Radiology,

Knoxville,

TN 37996-1600.

Abstract: Sodium perborate, a readily available and inexpensive reagent, efficiently oxidizes organoboranes. The reagent permits the oxidation of a wide variety of functionally substituted organoboranes. In nearly every instance, the product yields exceed those obtained using standard oxidation procedures.

Trialkylboranes sequences.

have

proven

to be versatile

The utility of the borane

reagents

intermediates

is centered

reactions and on the fact that they can be prepared containing groups,

eg. carboxylic

organoboranes generate

acid esters,

reagents includes

nitriles,

heating the boron reagent with 30% hydrogen of this standard

oxidation

a wide variety of important functional nearly

every synthesis

method for oxidizing

peroxide

reaction

of synthetic nature of their

reaction to remove organoborane

the target molecule. 2 The most effective

harsh nature

on the stereo-defined

etc. 1 Interestingly,

an oxidation

in a number

by-products

organoboranes

and 3 N sodium hydroxide

is often incompatible

involving or to

involves

at 5OC.3

with the functional

The

groups

present in the target molecules. In an attempted researchers

to minimize

side

have resorted to modifying

include the simultaneous modifications

7, Inconvenient

towards certain functional Sodium

perborate

of functionally

the standard

oxidation

procedure.

acids’s

reagents other than hydrogen

is an inexpensive,

stable

and easily

compounds

alcohols.

The product

yields

handled

Since sodium perborate substituted

is a mild oxidant, alkenes

oxidizes

are comparable

procedure. X7 The results of a comparative

series of functional!y

peroxide;

oxidant

methods

these reagents reactive

were hydroborated 1483

has an

of alkenylboronic

a variety of organoboranes to those

obtained

study are summarized

a comparative

which

agent 12, yet the application

has been limited to the oxidation

We wish to report that sodium perborate efficiently

standard oxidation

Successful

subtituents.7-11

to organoboron

the corresponding

organoboranes,

to handle e,s, difficult to prepare 10, or are themselves

excellent shelf life. The reagent has been shown to be a mild oxidizing of this reagent

substituted

addition of the base and peroxide 4 and the use of milder bases.516 Other

include the use of oxidizing

are often expensive

reactions

using the

in Table I.

study was performed

and oxidized

to

in which a

using both the sodium

1484

Table I Comparison

of the Efficiencies

of the Sodium

Perborate

and Hydrogen

Peroxide

Oxidation

Proceduces 0

Urganoborane

Yield, % e Sodium Hydrogen Perborate Peroxide

Product d

C

Tri-n-hexylborane

1-hexanol

f

94

94

Tri-l-(2-methyl)pentylborane

2-methyl-l

-hexanol

99

98

Tri-3-hexylborane

3-hexanol

99 g

98

Tri-cyclohexylborane

cyclohexanol

98 4

98

Tri-norbornylborane

exe-norborneol

98 o

98

aThe sodium perborate stoichiometric

procedure

quantity

adding hydrogen

peroxide

was prepared

bThe peroxide

(3 equiv),

(3 equiv.) as a 30% aqueous solution

(3 N) to the organoborane borane

was carried out for 2 h at room temperature

of Naf303~4H&I

(1 M in tetrahydrofuran)

via the hydroboration

oxidations

in water Using a

were carried out by

and 1 equiv. of sodium hydroxide

and heating to 50°C for 1 h.3 CThe organo-

of the corresponding

alkene

using

the standard

procedures outlined in ref 3. dAll products exhibited

physical properties and spectral characteristics

in accord with literature values.8

via GLC analysis.

hexylborane.

gOxidation

perborate procedure

eYields determined

fConversion

based on tri-n-

was performed using 1 eq of NaOH with heating to 5O’C for 30 min.

and the standard procedure. 3 The results are presented in Table II. Only the

major product is reported in Table II; isomeric alcohols are also formed due to the mesomeric inductive

effects

comparable

of the functional

to those obtained

often exceed those obtained

substituent

during

using trimethylamine

hydroboration.14

N-oxide

using the standard oxidation

(a relatively

procedure

oxidation

perborate procedure. THF contained

of tri-(3-chloro-2-methyljpropylborane 3-Chloro-2-methyl-l

in a dry, nitrogen-flushed,

-propene 25mL

nitrogen inlet tube, a gas outlet tube connected stirring bar and maintained and hydroboration

and the aqueous

isolated by distillation.

can be used.

in 1.5 ml_ of with a

a magnetic

of dimethyl sulfide-borane

The mixture was stirred at 0°C

To the resultant tri-(3-chloro-2-methyl)propylborane

water (3 mL) and sodium perborate (1.38 g, 9.0 mmol).

at room temperature

phase was washed

to a mercury bubbler, a thermometer,

borane-THF

for 2 h, and then brought to room temperature.

were separated,

of the sodium

flask. Which was equipped

by dropwise addition of a 2.0 M solution

Alternatively-,

in THF was added sequentially, was maintained

and

and cyclization.15

is representative

(0.81 g, 9.0 mmol) was dissolved

three-necked

reagent

under a positive pressure of N2. The flask was cooled to 0°C (ice bath)

was initiated

complex (1.5 mL, 3 mmol).

expensive

and

yields are

because the strong base used

in the peroxide method often leads to side reactions such as elimination The

The product

with saturated

(water bath) for 2 h while vigorously phase

extracted

NaCl solution

stirring.

The mixture

The two phases

with ether (3 x 5 mL). The combined (5 mL), dried

(MgS04).

organic

and the product

was

1485

Table II Comparison

of the Sodium Perborate and Hydrogen

Functionally

Substituted

Organoboranes

Peroxide Oxidation

Procedures for a Series of

a

Alkene

Yield % d NaBO3 e H202/0H-

Product b,c

f

CH, H,C

SCHZi:CH

CH,CH=

/ (t -

SCH2;HCH20H

CH2

P YH3(CH2)2 CH= C-0-CH

\

H,C

2

0 CH2

/ o- -

\

were formed via the hydroboration cAlI products exhibited

in accord with literature values.8 out for 2 h at room temperature oxidations

solution

77

89

a6

83

35

CH3

!-O-;H(CH2)40H

ClCH2CHCH20H

major product is indicated.

aqueous

81

fH3 CH,

aThe organoboranes

fThe peroxide

85

CH2 CH2CH20H

YH3 ClCH2C=

92

physical

properties

in water using a stoichiometric out by adding

of sodium

bOnly the

and spectral characteristics

eThe sodium perborate procedure was carried

oBy GLC analysis.

were carried

and 1 equiv.

of the alkenes listed in the table.

hydroxide

quantity of NaBOsa4H20

hydrogen

peroxide

(3 equiv.)

(3 N) to the organoborane

(3 equiv). as a 30%

(1 M in tetra-

hydrofuran) and heating to 50°C for 1 h.3 The use of sodium perborate as an oxidizing to the standard

oxidation

handle than hydrogen borane syntheses

procedure.

peroxide.

is currently

UNOWLEDGEMFNT support of this research.

The reagent

The application

agent for organoboranes is inexpensive, of the perborate

is a viable alternative

more stable and far safer to oxidation

to a variety

organo-

under investigation.

We wish, to thank the Department

of Energy (DE-FG05-85ER60434)

for

1486

REFERENCES

1. (a) Pelter.

A.; Smith,

K.; Brown,

Methods):

New York,

New York,

1975.

1988.

H. C. Borane

Reagents.

Academic

A.; Smith, K. Comprehensive

(c) Pelter,

Ollis, W. D. (Eds), Pergamon

Press Inc. (Best Synthetic

H. C. Organic Synthesis

(b) Brown,

Press: New York 1979.

via Boranes, Wiley Interscience:

Organic Chemistry, Barton

D. H. R.

G. W. Act. Chem. Res. 1984,

(d) Kabalka,

17, 215 2.

(a) Brown, Takacs,

J. V. N. Vara J. Am. Chem. Sot. 1986, 708, 2049. (b) Evans,

H. C.; Prasad,

J. M.; McGee,

1988, 1 IO, 3560-78. Matteson,

L. R.; Ennis, M. D.; Chapman, (d) Ikeda,

H. J. Am. Chem. 1986, 708, 483.

M. E.; Caille,

J. C. J. Org. Chem. 1988,53, 477.

(i) Pelter,

Tetrahedron Lett. 1985, 26. 5093. (j) Roush, W. R.; Palkowrtz, 1987, 52, 316. (k) Uenishi, 109, 4756.

(I) Zweifel,

T. M. Synthesis,

L. A.; A.

M. J. J. Org. Chem.

1988, 129.

G. ,/, Am. Chem. Sot. 1959, 87, 1512.

5. Brown, H. C.; Kabalka,

G. W.; Rathke,

6. Brown,

E.; Coleman,

H. C.: Knights,

(a) Kabalka,

(h) Paquette,

A.; Buss, D.; Pitchford,

R. W.; Kishi, Y. J. Am. them. Sot. 1987,

J.; Beau, J. M.; Armstrong,

6.; Shoup,

R. M.;

H. C. Org. React. 1963, 73, 1.

G.; Brown,

4. Brown, H. C.; Zweifel,

7.

S.; Kennedy,

A. D.; Palmer,

(e)

S.; Sato, T.;Kim,

(f) Masamune,

T. A. J. Am. Chem. Sot. 1986, IDS, 8279. Masamune,

J. S.; Houk, K. N.; Wu, Y. J. Am. Chem. Sac. 1986, 708, 7404.

Peterson, Okazaki.

3. Zweifel,

E. M. J. Am. Chem. Sot.

K. T.; Carreira.

N.; Arai, I.; Yamamoto,

M. L. J. Org. Chem., 1987, 52, 5116.

D. S.; Peterson,

B.; Wollman,

D. A.;

G. W.; Hedgecock,

M. W. J. Am. Chem. Sot. 1967, 89, 4528.

R. A. J. Am. Chem. Sot. 1969, 91, 2144.

H, C. J. Org. Chem. 1975, 40, 1776.

M. R. J. Org. Chem. 1986, 57, 1330. (c) Soderquist,

J. A.; Anderson,

(b) Soderquist,

J. A.; Najafi.

C. L. Tetrahedron Lett.

1986, 27, 3961.

8. Brown,

H. C.; Midland,

9. Pelter, A.; Hutchings, 10, (a) Midland, Nelson,

M. M.; Kabalka, M. G.; Smith,

M. M. Preston.

J. V. J. Am. Chem.

G. W. Tetrahedron

1986, 42, 5523.

K. J. Chem. D 1970, 1529.

S. B. J. Org. Chem. 1980, 45, 4514. Sot.

1979,

707, 6120.

(c) Vedejs,

(b) Evans

E.: Engler,

D. A.; Vogel, D. A.: Telschow,

E.: J.

E. J. Org. Chem. 1975, 43, 188.

11. Koster, R.; Morita, 12. (a) McKillop, Duranceau,

Y. angew. Chem. Int. Ed. Eng/. 1966, 5, 580.

A.: Hutchings, S. J.: Milier,

M. G.; Smith,

J. F.; Kosiba,

K. Tetrahedron

M. L. Synthetic

1987, 43, 1753.

Communications

(b) Gupton,

J. T.;

1988. 78, 937. (c)Ding,

X.; Ge, Y.; Teng, Z.; Fan, J. Yiyao Gongye, 1987, 18, 193. 13. (a) Matteson,

D. S.; Moody,

R. J. J. Org. Chem. 1980, 45, 1091. (b) Matteson,

J. J. Organomet. Chem. 1978, 752, 265: (c) Matteson,

D. S.; Moody,

Chem. Sot. 1975, 97, 5608. Sot, 1968, 90, 2906.

14. Brown,

H. C.; Gallivan,

R. M. J. Am. Chem.

15. Brown,

H. C.; Rhodes,

S. P. J. Am. Chem. Sot. 1968, 91, 2149.

(Received

in

USA 6 January

1989)

D. S.; Moody,

R. J.; Jesthi,

R.

P. K. J. Am.