aibn: A formal synthesis of steganone

Tetrahedron Letters,Vol.29,No.24,pp Printed in Great Britain

RADICAL

MEDIATED

INTRAMOLECULAR A

N.S. Garware

:

Despite

Research

have

Department

Pune

generated

increasing

to date,

have been

fashion.

where

of Chemistry,

- 411 007

(INDIA).

by the reaction

been

coupled

biaryl

coupled

of aryl

bromide

intramolecularly

(1 mmole)

and

was obtained, anticipated

&*

AIBN

(25%

with

to an

subsequent

reactions

in compound

-1 and 2.

by weight in poor

refluxed

our

benzene

or toluene

studies

towards

in benzene

of 1) for 18 hours.

yields

is no and

Ru3SnH/

in an inter or intramolecular

reports

was

there halides

(23%).

This

(50 ml) with A phenanthrol

did not have

is

intra-

Bu3SnH indeed

the

2 but the isomeric structure 5. The structure was 5 and also by comparison with authentic samples of data by photocyclisation

of 6 and -7 respectively

and

ethanolysis.

The mechanism

which

of formation Presumably

is not clear.

of 5_, in the reaction

a Spiro

intermediate

then

rearranges

to 1.

In another

experiment

, the bromoenamine

,

was

standard

procedure

and AIBN

(20% by weight

gave 2 in 66% yield. synthesis Similar

converted

ring either

of these

reactions, from aryl

structure

on spectral

a formal

generated

communication

(0.5 mmole)

although

2 and 5_, obtained

attack,

aryl

in many

This

in radical

radicals

witn

coupling

Compound

interest1

aryl

Interestingly

molecular

AIBN,

Centre,

of Poona,

and AIBN,

used as a solvent.

based

:

TRIBUTYLTINHYDRIDE/AIRN

ring.

report, AIBN,

USING

+ .OO

SYNTHESIS OF STEGANONE * Narasimhan and Indrapal Singh Aidhen

Aryl radicals,

tributyltinhydride aryl

ARYLATION

0040-4039/88 $3.00 Perqamon Press plc

FORMAL

University

ABSTRRCT

2987-2988,1988

refluxed

2 has already

to the above

gave

(3c:3c' ::1:6)- separated Acknowledgement

:

a

5 in good

thanks

CSIR 2987

obtained

by

(3.3 mmole)

and

thus

f, was achieved. 9a,b,c

were

yields

(50-80%).

of two phenanthrylamines

by HPLC.

IPS Aidhen

Bu3SnH/

by ipso

in 2 to 2.5 hrs,

to steganone4

steganone

the bromoenamines

mixture

Bu3SnH

complete

converted

phenanthrylamines

9cr as anticipated,

mmole),

(10 ml) with

lignan,

procedure,

9 (2.5

reaction,

been

of the antileukemic

to the corresponding

The enamine

in benzene

A clean

of 9).

of 1 with

8 is formed

for a fellowship.

also

2988

OMe

6Me z

8.

6Me L OMe

6Me

0 OCOCH3

h V/Pyrex Benzene

2

fi

R=R,=OMe

2

R =R2=OMe,

(C2H5)3 N

, R2=H Rl=H

n

R,=R2=R3=OMe

&

R, =R2=R3

-9b

RI =R3=H,

3

R,=H,

ti,, =H R2=OMe

R2R3=-OCH20-

3

RI =R2= R3= OMe

3a

R,=R2=

-3b

Rl=R3=H,

-3c

R,R2=OCH20

, R3=H

R2 R3 = OCH20

aRI= H

R3= H R2=OMe

References 1. 2.

B. Giese, Tetrahedron, 43 3541 (1987). -' S.F. Dyke, E.P. Tiley,

41 -' W-C.

3887

(1985):

M. Ramiah,

iJhite, D.P. Gale,

Tetrahedron,

Tetrahedron,

I,

1219

(1975).

3.

UV Amox (MeOH) : 370 (log E 3.00), 345 (3.40), 320 (4.07), 290 (.71), 255 (4.92) nm. PMR (CDCl & : : 5.90 (lH, bs, exchanges with D20), 7.80 (lH, s), 7.60 (lH, S7 , 7.40 (111, s), 7.20 (lH, s), 6.00 (2H, s) and 4.00 (9H, 3s). Compound 2 expected to have C-4 proton between 8.7 to 9.0 due to deshielding-by C-5 methoxyl.

4.

D. Reeker, L.R. 1674 (1977).

5.

PMR spectral data of aromatic protons of phcnanthrylamines (CDCl 6 3 (m.p. 130-310), 8.9 (lH, s), -1.60 (li!, s), 7.00-6.85 (ZH, 2s ?: Ja (m-p. 113-15"), S.05 (lH, s), 7.65 ((lH, s), 7.60-7.20 (5H, m): % (m-p. lOlo), 7.95 (lH, s), 7.83 (3H, m), 7.32 (2H m): z (R,R2= -OCH20-, R3=H: m.p. 156-57"), 8.05 (lH, s): 7.65 (IH, s), 7.24 (3H, m). ~~,i~l6~,(:~~3;s~CH2O-, m.p. lROe), 7.75-7.60 (3H, 3~1, . (Received

Huges,

.

R.A.

Raphael,

.

in

UK 18

February

1988)

J.Chem.Soc.

Perkin

Trans.

I,

) :