An expeditious approach to the synthesis of Angular Triquinane

oo4o-4039192 $5.00 + .a0 PargamonRarL&d

Teuahedron L.emm.Vol. 33, No. 25. pi. 3687-36’0.1992 Printedin GreatBritam

AN EXPEDITIOUS APPROACH TO THE SYNTHE!ilS OF ANGULAR TRIQUINANE Yadav

Praveen Kumar T.K. of Chemical Technology,

J.S*,

Indian Institute

A flexible approach for the synthesis mediated reaction is described.

ABSTRACT:

free

radical

A variety Prominent

of

angular

among

them

(IV),

and

pentalenene4

over

strategies

the

involving

trlcyclopentanoids

are

isocomene’

subergorgc

cyclopenta(C)-pentalene chemists

and SadgIl Hyderabad

system past

few

sequential

(I),

acld5

of years

have The

these and

annulations’

been

isolated

lead

to

(II), has

the

from

development

and tandem radical

products.

acid3

challeqlng

attracted

using

natural

retigeranic

synthetically

compounds

India

of Angular Triquinane

silphenene2

(V).

V.R.

500007,

synthetic of

(III),

decahydro-

many

organic synthetic

cycllsations7.

I COOH

0 V

\\” @

for

Ueno’ s9 methods

We studied

Stork’s8

and

synthesis

of

triqulnane

the

moiety.

Scheme -1

OEt

Ott

i

of radical The

initially

cycllzation generated

of bromoacetals radical

from

(1) 1

3688

predominently

attacks

substituents bearing

radical

cyclisation bromoacetal

(1)

lncornorated alcohol

moiety

was found such

would

governed

cyclisation

in

the

we envisioned

the

readily,

stereochemistry always

oxa-triquinane

synthesis

present

of be

required The

enone’O.

cyclopenta-2-en further

was

which

bromoacetal

(6)

nonselective

l-one

with

if,

the

the

derived the

of

attack

group. side

The chain

be

of such would

resultant

carbon

enabling

further

2

describe

the

prepared

butenyl

above

to the

bromoacetal

stratagem

new

to the optically starting

bromide

according

to

could

of the cyclisation

hydroxyl the

group

from the bromoacetal face

from

was

at

using

6

active

give I1 and Ducker .

produced

3 to

dienol

ptocedure9a.

standard

on

the

cyclopent-2-

with

of Ansell -78°C

for

ttiquinane.

2-methoxy

condensed

procedure

DIBAL-H in dichloromethane

converted

thus obtained,

to

cyclisation bifacial

hydroxy

with

be extended

was

from

reagent

4 on reduction

the

3 -facial

cyclisation

2).

we

can also

bromoacetal

Grignard

2(buta-4-enyl) Compound

which

hand,

tandem

Thus,

to the

where

“syn”

(Scheme

communication,

of triquinane

The

1).

that

the radical

rq,

Scheme-

In

(Scheme

to the carbon

other

undergoes

wherein

(la)

respect

On the

which owing

radical

with

bond.

cyclisation

~111

geometry

cyclisation.

(lb)

21% yield

a situation,

(7a)

to give

further

forming

e-face,

“trans.”

to be unsatisfactory

undergo

by

radical

the

product

on the cyclopentene

(5)

bearing

“~1s”

on to the olefinic

overcome

from

r&rig have

preventing to

oxa-triquinane

of the radical

be

rise

olefin

formed

thereby

gives

oroduce

fo

the

on the newly

5

The

of sodium

in t-butanol

of tributyltinchloride 8 in At

to the this with

C-9 13 C NUR spectrum the value of methyl carbon from the as a- by correlating 12 13 which was also observed by several other workers . those of reported values

Having complete

of

secured the

the

tricyclic

synthesis

transformations

on

the

TFA and the resulting bromide

to

produce

of

acetal

hemracetal diol

our next

triquinane

oxo-ring. in

on

the

First,

moiety. the

was opened

70% yield.

The

task

was to construct

This

was

trlcyclic with

three

diol

was

achieved

acetal

was

equivalents oxidized

the by

third simple

hydrolysed of methyl

with

Jones’

ring

and

chemical with

90%

magnesium reagent

to

3689

obtain

the

ethanollc

dlketone

KOH, yielded

55% yield dlol

have

desired

of optically

of

a

novel

dlketone

tricycle

IO was also

trlquinanes

active

the

9-methyl

converted

presented

synthesis

and finally

compound

was eventually

we

stereospeclflc

the

Slmllarly,

13a.

1 lb which Thus,

preparation

in 75% yield

and

(6.3.0.0.“5)

opened

to triqulnane would

tricyclic

natural

Sctwllw

- 3

with

find

with

20%

unde-4-en-3-one

3 eq.

13b In 52% yield

operationally

which

on cyclodehydt-atlon

feasible widespread

of

EtMq6r (Scheme

aoproach application

in

to give 3). for

the

in the

products.

13b R = CH3 Reagents

:

a)

Mg ,&+e’-.Br,HCl,

-s-oEt, t-Butanol Ether,

HzSOr,

DCM , 0.--l , ref lur ;

; 6) DIBAL-H,

; d) NaBHaCN

c) Jonrr’oxidation,

RT ; h) 20%

KOH,

ethanol,

(lcq),

OCM,-7g.C AIBN

O*C ; 1) 90%

rrflux.

;

c) NBS,

kat),BujSnCI TFA ; g)

(cat),

Mg , RCHzBr,

3690

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