Ring isomerization of flavones. New synthesis of oroxylin-a and 7-methyl-oroxylin-A

Tetrahedron LettersNo.48,Pp, 4281-4282,1965. PergamonPress Ltd. Printedin GreatBritain,

KING ISCi'ld~~IZATION 03 %l,AVi)IGS.

NX\;, S.J!;U’TH~~SIS OF OROXfLIN-A AND 7-KETHYL-CWXYLIN-A J6zsef VQrady Department of Organic Chemistry, Technical University Budapest. (Received24 September1965) In a preliminary commttnication [l] we already have described a new method of ring isomerization by which both polyhydroxy-isoflavones and their O-methyl or 0-benzyl derivatives may directly be isomerized.

RO

RO octl3

a: R=H b: MI,-C& I.

c: X&H

3

II.

!;e now report on the extension of this method to the group of the flavones. At present our method is unique with respect to its suitability for effecting direct ring isornerisation of flnvones in alkaline media.

:,a starting materitils 7-benzyl-rogonin /Ib/ [2] and .

7-metilJl-

-:?o_.or,in /Ic/ have heen ayzt:::zsieedbv " garti:ll "enz;latiori and 7.et':;lnti_cn, rze~,ectivelj, of ::'o::o:.ir. [3,41.

4283

4202

No.40

Isomerization alcohol

has been effected

under anhydrous

carbonate.

4fter

destillatioi

treatment

Conversion

already

has been brought

process.

oroxilin-ii

of

sulfuric

,/IIa,

/IIc,

of

about

Chim. Acad.

Sci.

this

acid

mp.:

in both

and steam Co,

[7],

160-162

cases

however

Co,

lit. Co,

from

almost

the

quanti-

to ‘I-methyl-oroxylin-A

debenzylation

details

of potassium

have been isolated

being

mp. : 220-221

henzyl

rap. : 165-166

7-methyl-wogonin

Catalytic

Experimental in hcta

dilute /IIb,

the yield

tative.

step

with

respectively,

mi.xture,

with

in the presence

and 7-methyl-oroqylin-A

[6] : 155-156’/,

reaction

conditions

7-benzyl-oroxylin-A

[ 51 :164-166’/ lit.

by refluxing

of

lit.

onlj

by a multi-

the former

[ 51 : 218-220

work shall

shortly

gave Co/.

be published

Hung.

References: 1.

J. Vtiady:

2.

K. Venkateswara Proc.

Tetrahedron

Indian Shah,

3.

3.C.

4.

S. Battori:

Rao,

Acad. C.R.

Letters,

submitted

L. Visweswara

Sci.

g,

for

publication.

Rao and T.R.

Seshadri:

13 /1948/.

Mehta and T.S.

Weehler:

J.

Chem. Sec.

l&,

1555 /1938/. Lcta

Phytochim.

2,

99 /1930,

Tok.yo/ c 1931,

I.

1761i. 5.

R.S.

Sarin

and T.R.

Seshadri:

J.

Sci.

1r.d.

.!esearch

598.

117 /17X/. 5.

G. Sargellini:

7.

L. >‘ar

ki3.E,

Gazz. 1,

.

Hajor

Chim. Ital. und J.

2,

Strelisky:

47 /lY19/. Chem. Eer. 96, /1?63/.

1684