CATECHOL

1

Catechol

1

OH

OH

[120-80-9]

C

6

H

6

O

2

(MW 110.11)

InChI = 1/C6H6O2/c7-5-3-1-2-4-6(5)8/h1-4,7-8H
InChIKey = YCIMNLLNPGFGHC-UHFFFAOYAA

(reagent for heterocycle synthesis; allylation catalyst; carbonyl

protecting group; transition metal ligand)

Alternate Name:

pyrocatechol.

Physical Data:

mp 104–105

◦

C; bp 119–121

◦

C/10 mmHg;

d

1.344 g cm

−3

; sublimable (vp 1.0 mmHg, 75

◦

C); steam

volatile.

Solubility:

sol benzene, acetone, ether, ethanol, 2.3 parts water,

pyridine, aqueous alkali; slightly sol chlorinated solvents.

Form Supplied in:

colorless needles (or plates).

Purification:

recrystallization from toluene; distillation.

Handling, Storage, and Precautions:

toxic (readily absorbed

through skin); irritant; causes burns. Light and air sensitive.
Explodes on contact with conc. HNO

3

.

Original Commentary

Bruce A. Barner
Union Carbide Corp., South Charleston, WV, USA

Alkylation and Heterocycle Synthesis. Catechol undergoes

many of the reactions characteristic of phenols, and as such is
used to prepare o-alkoxyphenols, o-dialkoxybenzenes, and
heterocycles.

1

The high yield preparation of five-membered

o

-phenylene heterocyclic systems from catechol is particularly

common, and includes 1,3,2-benzodioxaborole from diborane
(eq 1) (see Catecholborane),

2

methylenedioxybenzene from

diiodomethane,

3

o

-phenylene carbonate from phosgene,

4

1,3-

benzodioxoles from allenic derivatives,

5

o

-phenylene chloro- and

bromoboronates from the respective boron trihalides,

6,7

and

o

-phenylene phosphorochloridite from phosphorus trichloride.

8

Larger heterocyclic ring systems, such as 1,4-benzodioxanes
(eq 2)

9

and dibenzo- and dicyclohexyl-18-crown-6 polyethers

10

are prepared in good yields using alkylations of catechol.

OH

OH

O

B

O

H

BH

3

, THF

(1)

0–23 °C

80%

O

OTs

K

2

CO

3

, DMF

60 °C

75%

OH

OH

O

O

OH

(2)

Allylation Catalyst.

Bis(catecholato)allylsiliconates, pre-

pared in situ from catechol, triethylamine, and allyl(trialkoxy)-
silanes, are effective allylating agents for aldehydes (eq 3).

11

Good

yields of homoallylic alcohols are obtained in a regiospecific man-
ner.

PhCHO

Ph

OH

erythro

:threo = 1:9

catechol, Et

3

N

CHCl

3

, reflux

88%

Si(OMe)

3

(3)

Carbonyl Protecting Group.

Ketones and aldehydes

react with catechol under acidic conditions to form cyclic acetals
(eq 4).

12

The acetals formed are more stable to acid than ethylene

acetals.

13

Cleavage of the o-phenylene acetals of α-unbranched

and aromatic ketones with BBr

3

gives geminal dibromides and

vinyl bromides, respectively (eq 5).

14

t

-BuCHO

TMSCl, CH

2

Cl

2

91%

OH

OH

O

O

H

t

-Bu

(4)

BBr

3

CH

2

Cl

2

, 0 °C

83%

O

O

Et

Et

Et

Et

Br

Br

(5)

Transition Metal Ligand. Catechol binds readily to virtually

all transition metals, giving catecholato metal complexes.

15

The

σ

- and π-donating properties of catecholato ligands,

16

as well as

other hydroxo ligands,

17

are postulated to stabilize unsaturated

organometallic derivatives.

First Update

Aileen F. G. Bongat & Alexei V. Demchenko
University of Missouri - St. Louis, St. Louis, MO, USA

Acylation.

Condensation reactions between catechol and

carboxylic acids or their derivatives are very common. The
reactions of catechol with esters can either be catalyzed by a
base

18

or an acid

19

(eq 6). Carboxylic acids couple with catechol

in the presence of dicyclohexylcarbodiimide (DCC) and catalytic
4-dimethylaminopyridine (DMAP, eq 7).

20

O

O

O

O

O

rt, 3 h, 83%

(6)

OH

OH

p

-TsOH, DCM

OH

+

Avoid Skin Contact with All Reagents

2

CATECHOL

OH

OH

OC

5

H

11

OC

5

H

11

OC

5

H

11

O

OH

+

OC

5

H

11

OC

5

H

11

OC

5

H

11

O

O

OC

5

H

11

OC

5

H

11

OC

5

H

11

O

O

DCC, DMAP

CH

2

Cl

2

, rt, 20 h, 90%

(7)

Oxidation.

Oxygen (O

2

) readily oxidizes catechol to o-

quinone in the presence of a suitable catalyst. In enzyme-catalyzed
transformations of this type, oxidases, such as tyrosinase

21

and laccase,

22

are often the catalysts of choice (eq 8). Salts

such as PbO

2

,

23

Ag

2

O,

24

or a combination of Pd(OAc)

2

-

Cu(OAc)

2

25

have also been employed as catalysts for this reaction.

Furthermore, catechol can be oxidatively opened to form useful
synthetic intermediates, for instance the (Z,Z)-monomethyl
muconate shown below (eq 9).

26

OH

OH

O

O

cat laccase, O

2

(8)

buffer, rt

O

2

, pyridine

80–85%

OH

OH

Cu

O

Cu

O

py

Cl

Cl

Py

Me

Me

COOH

COOCH

3

+

(9)

Functional Group Interconversion. Catechol can be trans-

formed into more reactive intermediates through selective or
global conversion of its hydroxyl moieties. In the example below
(eq 10), catechol was converted into 1,2-bis(nonaflyl)benzene
since the aromatic sulfonate functionality is more easily replaced
by a cyano group in the next step.

27

It was noted that catechol

reacted with polyfunctional 2-(chloroseleno)benzoyl chloride
in a different way than that of aliphatic alcohols. While in the
latter case faster O-acylation with the COCl moiety was
detected, reaction with catechol favored the O-selenylation
product (eq 11).

28

OH

OH

OSO

2

C

4

F

9

OSO

2

C

4

F

9

CN

CN

1. Et

3

N

2. C

4

F

9

SO

2

F

Pd(PPh

3

)

4

/Zn(CN)

2

(10)

DMF, 79%

DMF, 83%

OH

OH

+

C(O)Cl

SeCl

C(O)Cl

Se

HO

O

(11)

CH

3

CN, Et

3

N

rt, 71%

Electrophilic Aromatic Substitution Reactions. By virtue

of its aromatic nature, catechol typically undergoes electro-
philic aromatic substitution reactions such as halogenation,

29

carboxylation,

30

sulfonation,

31

and Friedel–Crafts acylation

32

(eqs 12–15). In addition to these common classes of aromatic
substitution reactions, a solvent- and catalyst-free regioselective
Mannich-type reaction of catechol resulting in the exclusive
formation of o-substituted aminomethylated derivatives has been
recently reported (eq 16).

33

OH

OH

OH

OH

Br

Br

Br

2

, CCl

4

(12)

80%

OH

OH

OH

HO

COOH

HOOC

(13)

NaOH then CO

2

, 80 atm

200

°C, 48 h, 54%

HSO

3

Cl

110

°C, 1.5 h, 37%

OH

OH

OH

OH

SO

2

Cl

ClO

2

S

(14)

OH

OH

O

O

O

O

O

OH

OH

(15)

+

AlCl

3

/NaCl

OH

OH

OH

HO

N

CO

2

Et

CO

2

Et

(16)

1 equiv ethyliminodiacetate

excess (CH

2

O)

n

, 50

°C, 70%

Formation of Zwitterionic Pentacoordinate Silicates.

Recently, catechol was found to mediate Si–C and Si–O bond
cleavage reactions in dialkoxy- (aminoorganyl)organylsilanes
to afford spirocyclic λ

5

Si–silicates with an SiO

4

C framework

(eqs 17 and 18).

34

These novel Si–C cleavage reactions were

applied to novel “traceless” silicon-based linkage formation and
cleavage strategies for the synthesis of aromatic compounds on
solid phase.

35

A list of General Abbreviations appears on the front Endpapers

CATECHOL

3

Si

OEt

Ph

N

O

H

H

OH

HO

O

O

Si

O

O

NH

O

H

H

(17)

H

3

C

Si

CH

3

O

CH

3

O

N

H

H

OH

HO

O

O

Si

O

O

H

H

NH

(18)

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2.

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3.

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4.

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4

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13.

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14.

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15.

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22.

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Avoid Skin Contact with All Reagents