A convenient one-pot preparation of glycosyl bromides as well as glycosyl acetates from benzyl glycosides using N-bromosuccinimide.

Tetrahedron Letters,Vo1.28,No.30,pp Printed in Great Britain

A CONVENIENT GLYCOSYL

ONE-POT

ACETATES

Hironobu

PREPARATION

FROM BENZYL

Hashimoto",

Department

0040-4039/87 $3.00 + .oo Pergamon Journals Ltd.

OF GLYCOSYL

GLYCOSIDES

Manabu

Shigeomi

Institute

3505-3508,1987

Kawa,

BROMIDES

USING

Yoshihiro

AS WELL AS

N-BROMOSUCCINIMIDE.

Saito,

Tomoko

Date,

Hori'co, and Juji Yoshimura

of Life

of Technology,

Science,

Faculty

Nagatsuta,

of Science,

Midoriku,

Tokyo

Yokohama,

227 Japan

Summary: Some conversions of benzyl glycoside using NBS were examined and one-pot preparation of glycosyl acetates and bromides An efficient 0-debenzylation at non-anomeric were developed. position was also observed.

Benzyl especially

group

has been

in the field

frequently

on glycocinnamoylspermidine, deoxy-a-D-xylopyranoside of azido

as well

hydrogenolytic hydrolysis

conversions

a selective

derivatives

as carbamate

deprotection

nor acetolysis'

this communication

groups.

for protection In the course

debenzylation

of benzyl

Furthermore,

to be applicable

like to describe

glycoside

of hydroxyl

group

of synthetic

studies

2-azido-2-

such as -I-4' was required in the presence In this case the generally used

is inadequate. proved

we would

of benzyl

used

of carbohydrates.

neither

for these

a convenient

into the corresponding

acid

compounds.

In

and one-pot

bromide

as well

as

acetate. It is well

known2

that benzyl

(NBS) to give benzaldehyde benzyl and

protecting

it was

various

found

treatment

in the following

group,

ether

via a-bromination. especially

that reaction provided scheme

alkyl

This

at the anomeric

of benzyl

several

reacts

glycoside

efficient

and Table.

Treatment

with N-bromosuccinimide reaction

center, with NBS

conversions, of benzyl

was applied

followed

which

by

are summarized

2-azido-2-deoxy-8-L-

-0

OCH,Ph + f

OCHPh Br

_J-

kaHC03

Br

y&~+ AcOK i

3505

to

of carbohydrates

3506

Table. Some Chemical Conversions of Benzyl Glycosides via Bromination with NBS Benzyl

Reaction

Entry

Methoda glycoside4

timeb

(1)

(2)

Yield Product5 8

3h

I)

2)

0.5 h 3.5 h

OAc

(2)

a1

(8)

61

AcO N3 2

I)

2) I)

2)

0.5 h 2h

60

10 min 5 min

a5

12 h

a7

12 h

ai ai (14)~

1) 22 h 2) 4h OAc

OAc 5

I)

2) 3) 1)

21 3)

15 min Ih 1.5

a5 (6)e

h

min 1.5 h 1.5 h

15

OAc (13)

a3 (ale

OAc

a) A: NBS(l.5 equiv), BaC03/CC14; B: 1) NBS(3 equiv)/CC14, 2) AcONa(l0 equiv)/AcOH; C: l)NBS(l.S equiv), BaC03/CC14, 2) AcONa(l0 equiv)/AcOH; D: l)NBS(2.7 equiv), BaC03/CC14, 2) HMPA(0.4 equiv); E: NBS(3 equiv), (PhC0)202(0.08 equiv), AcOK(8.8 equiv)/CHC13-Ccl4

(1:l);

F: I) NBS(3 equiv), BaC03/CC14, 2) AcOK(10 equiv); G: I) NBS(l.4 equiv), BaC03/CC14, 2) HMPA(l equiv), 3) AcOK(10 equiv)/AcOH b) For each step described in the method. cl The ratio of a- and fl-anomers was 3 to 1. d)

Obtained as an epimeric mixture at the benzylic position with a ratio of 3 to 2.

e) Recovered benzyl glycoside.

3507

lyxopyranoside

derivative

the corresponding

glycosyl

glycosyl

bromide

benzylic

bromination

proceed

rapidly

(1) with NBS bromide

from benzyl

in order

products,

but

in good yield

glycoside

mechanism

to prevent

seems

some

reactivity

of J_ and 2 may attributed

compound equiv)

caused

bromide

acetate

with

9: the second

3, 8 and

G).

acetate

a-acetoxy

derivative

a-bromo

further methoxide

of benzyl

added,

with

(1 mmol)

and heating

NBS

was continued

and acetic

acid

conventional

workup

A further

under

(1.4 mmol)

reflux, obtained

portionwise

two kinds

carbonate

Addition heating

of potassium

was observed

respectively,

one (16) in 14% yield. quantitatively by treatment

Q

AcO

N,

R=NHBoc

E

R=OAc

was

(1 mmol), (10 mmol)

by

of benzyl

4-O-

(17). When NBS (1 equiv) tetrachloride under

together

with

with NBS and catalytic

R=OBn

acetate

in the case

Furthermore,

&

in carbon

lo-15 min HMPA

of -17 in carbon 0-debenzylated derivatives,

15

A mixture

To this mixture

debenzylated

OAc

seems

(10) was -

acetate.

of this reaction

14% yields,

(0.5 mmol)

for 1.5 h followed

to a solution

0

chloroform

peroxide

is as follows:

prepared

R

of

derivative

for 20 min.

and then after

1.5 h.

of partically

in 50% and

2,

as the corresponding

in this reaction,

acetate

acetyl-2-azido-3-0-benzyl-2-deoxy-a-D-xylopyranoside was added

(entries

step of the

out in the presence

such as dibenzoyl

reflux

and further

gave glycosyl

aspect

9: the into the

(14) by treatment with sodium acetylation. Typical procedure for

and barium

for

(2.5 ml),

acid

An a-acetoxy

into glycosyl

(6 ml) was heated stirring,

acetate/acetic

be trapped

(1

step of

acetate

glycoside

glycoside

tetrachloride

converted

Although

initiator

by conventional

of benzyl

could

high

of

8 and

B and C, and the third

the reaction.

into glycosyl

followed

conversion

a radical

(entries

was further

is carried

5 and 6).

for promoting

converted

or potassium

intermediate

(entries

was used as a cosolvent, to be effective

sodium

of HMPA

for the formation

as 5 and 5

bromide

step of the method if the reaction

Moreover,

potassium

Glycosyl

G).

effect

(entry 4: the second

utilized

glycoside

The relative

of the starting

A remarkable

to be generally

carbonate

by-

The step II has

2.

3-22 h.

to the instability

step was observed

such benzyl

step of the method

corresponding

method

from

for

is, I may

Barium

by acidic

in entry

heating

interaction.

of this

D), and proved

the method glycosyl second

by 1,3-diaxial

for acceleration

accepted. caused

gave of

that

The step

(step II).

as shown

and needs

Formation

of two steps,

as generally

to be not necessary

an ionic mechanism

tetrachloride

(entry 1).

side reactions

presumably

carbon

may consist

(step I) and rearrangement

via radical

was added

in refluxing

-18 and 15, was totally O-

the last compound amount

could

1_7 R=Bn Bn N,

a

be

of bromine

R=Ac

3508

at room

temperature

hydrolysis

for

conventional

(induction

with

aqueous

time was observed),

sodium

As the reaction

carbohydrate

of benzylidene

acetal 6

by

and then by

using

NBS described

chemistry

H. Hashimoto,

with NBS has been widely

, chemical

into sugar bromobenzoate

in this

letter

conversions

could

used

for

of benzylated

provide

a new aspect

in

of carbohydrates.

References

1.

followed

hydrogencarbonate

acetylation.

its conversion

synthetic

19 h

of u-bromide

M. Kawa,

Y. Saito,

and Notes

T. Date,

and J. Yoshimura,

Carbohydr.

Res

(in contribution). 2. a) R. L. Huang

and K. H. Lee,

"N-Bromosuccinimide"

J. Chem.

in "Synthetic

Sot., 3,

Reagents",

5957.

John Wiley

b) J. S. Pizey, & Sons,

New York

(1974), pl. 3. K. Araki,

M. Kawa,

Sot. Jpn., 4. Compound

2,

5. New glycosyl (100 MHz

6 6.33

J3 4=7.0 2:'s Other

6.45

bromides

-8: 'H-NMR 18), 5.33

1 and 2 could

be characterized

while

Chem.

14-17 were --

1 H-NMR

only by

(s, MS),

1.45

(s, t-B;).

(d, Jl 2=3.0 Hz, H-l),

2.10

(s, AC),

Hz, H-3;,

3.14

2, lo,

and _11 gave

data

1.46

5.44

(dd,

(s, Boc).

satisfactory

elemental

analysis

and

data. (CDC13):

6 6.00

(dd, J2,3=3.5

Hz,'J4

5=10.3

[a]g5 +171.4'

(CDC13) : 6 5.25

(bd, J=8.0 CHC13,

Hz, NH),

1 :I mixture 5.19

2.16

is, PhCga),

6.99

(each s, OAcb), 3:2 mixture 5.57

6.85 (s, Phcgb), 2.14 (s, OAca), (s, PhCHa), 6. J. Gelas, Adv. Carbohydr. Chem. Biochem., 2, 1987)

4.96

1144

(s, t-Bu).

'H-NMR

4.90

(CDC13)

(dt,

(dt, J3,4=J4,5=9.5

(s, PhCHb), 1.47

Hz, H-

(dd, J2 3=3.O Hz,

(s, AC),

(d, J, 2=3.2 Hz, H-lb),

(d, Jl,2 =3.4 Hz, H-la),

9 April

(d, J1,2=2.5

of two epimers);

Hz, J4 5 ,=5.8 Hz, A-4a),

(c=l.8, CHC13,

in Japan

5.93

Hz, J3,4 18.5 Hz, H-3c.), 5.22

4.74

+135°,(c=1.1,

(d, J, 2=3.5 Hz, H-lu),

=6.1 Hz: H-4b) , 6.87 J4,5' (each s, OAca), 2.10 and 2.15

(Received

paper',

(dd, J2 3=3.O Hz, H-2),

Hz: 11:

Bull.

4.46

:d, J 1 2=3.6 Hz, H-la),

J3 4=10.1

in the contributed

(d, Jl 2=l.0 Hz, H-l),

J3 4=8.0 Hz, H-38),

11): [a]25

and J. Yoshimura,

in CDC13).

new compou;ds

spectral

65.48

H. Hashimoto,

(1986).

l-4 will be reported -3 previously .

reported

7:

Y. Saito,

3137

2.03 and

(s, t-Bu).

of two epimers);

'H-NMR

(d, J, 2=3.6 Hz, H-lb), 2.15

2.17

(L, OAcb),

71 (1981).

6.29

6.95

(bs, NH)