[3+2] Cyclopentane annulation reactions using organoiron reagents. Hydroazulene synthesis.

Tetrahedron Letters,Vo1.25,No.20,pp Printed in Great Britain

2097-2100,1984

[3+2] Cyclopentane Using Organoiron

Annulation

Reagents.

0040-4039/84 $3.00 + .OO 01984 Pergamon Press Ltd.

Reactions

Hydroazulene

Synthesis.

J. C Watkins and M. Rosenblum* Department

of Chemistry,

Brandeis

Walthrrm, Massachusetts

University

02254

Summary: A one step synthesis of 4-ketohydroazuleneiron troponeiron tricarbonyl is described.

We have shown that tropyliumiron reactions allenyl

with (nl-ally1

congeners,

tricarbonyl

complexes -6,7 and 2 from

enters

into stepwise

Fp complexes 1 LFp=n5-C,H,Fe(CO),J

and their propargyl

and that these products may be further

electrophiles

or nucleophiles.l

hydroazulenes

funtionalized

Such sequences

provide

[3+2] cycloaddition

elaborated

through

simple and efficient

at C-l, C-2 or C-4.

and

reaction

with

entry to

H

. + Q

FP

FP

+Fe(CO)x

In order to further the construction tropyliumiron the readily addition -78',

examine

of guaianolide

complexes available

by reaction

in methylene

as partners

troponeiron

chloride

in these cycloaddition

tricarbony12

solution.

Treatment

These reactions

product of cycloaddition.

ligand

reactions.

may be suitably triflate

nucleophile

or n-butylboryl

of the intermediate

complexes

may be depicted

tropyliumiron

complex 2 through

for

2097

cycloat

trimethylsilyloxy-

(6,7,8) ---

as proceeding

followed

or by

as the sole through

terminal

tricarbonyl

the uncomplexed

toward

triflate,

(1,4,5), ---

at C-l, the least hindered

in a 6-substituted

especially

We now find that

activated

of the resulting

has been found to yield 4-ketohydroazulene

of the pentadienyl

of this sequence,

salts 2 with a number of Fp synthons

attack of the organometallic

by closure

potential

we have begun a study of functionalized

with either trimethylsilyl

di-n-butylboryloxytropyliun hydrolysis,

the synthetic sequiterpenes,

initial

carbon

atom

cation 2, followed

enol double

bond.

This

2098

sequence

is illustrated

tropylium

cation.

summarized

below for the reaction

Cycloaddition

products

of Fp(n'-allyl)

complexes

with the

formed with a nunber of Fp synthons

are

in Table 1.3

02

n ,”

7

k.1+

FP~

Fp R

+Fe'(CO)3 -2

Fe(k0j3

1.

1

Z = SiMe3,

Table

+Fe(CO$

H;i

B BuZ

I

Cycloaddition Activator

Nucleophile

R

FP

H

a

H

b

Me

b

\

Products Product H FP

R -

% Yield

H

58

H

60

Me

62

Me

23

1

a a

Me Fp\

92

Me

ti k

62c -4

Fp-1

26

\

55

-5

a.

Structural

assignments

presence

of 4-proton

5.2-5.8

and 2.4-2.6)

the spectra

c. the TMS group is lost during the reaction

b. B+BOTf

TMS OTf

of these as 4-ketohydroazulene

NMR resonances

characteristic

and of low frequency

of all cycloaddition

products.

carbonyl

complexes

of the dieneiron absorption

Shift reagent

follow from the tricarbonyl

in the IR (v

experiments

group

(a

1620 cm-l)

in

with Eu(fod),

on 7

2099

confirm

the placement

stereochemical group,

of the Me group

relationship

of the hydrogens

in all of the cycloadducts,

nucleophiles

to pentadienyliron

A typical

experimental

at C-l in this substance.

follows

at C-3a, 8a with respect

from well precedented

illustrative

tricarbonyl

of the method

of troponeiron

chloride

was placed under argon and cooled to -78'.

4 (R=Me) dissolved

disappearance

carbonate

After 3 hours

of absorption

in 10 ml of methylene

for 2 hours

through

and stirring

at room temperature

celite,

solvent

tri-

of the soluof the start-

1:l).

(basic,

The trailing

activity

for 12 hours.

yellow

bands were collected

was

refluxed

for

and solid potassium

The solution

IV) by the dry column technique

The solution

and was finally

ethanol

and the product was chromatographed

was then filtered on silica gel

and chromatographed

(11x2 cm nylon,

again

EtOAc-Skelly

(R=Me) as an amber oil.

The use of excess 4 (R=Me) is advantageous presence

A

methylene

of di-n-butylboryl

and cooled to -78".

by adding absolute

was removed

1:2) to give 0.74 g of 1

Yellow

An equivalent

at -78', an ir spectrum

at -78', then warmed to room temperature was quenched

on alumina

of

is as follows.

at 1631 cm-' characteristic

chloride

The reaction

(EtOAc-Skelly,

addition

To this solution was added via cannula, 2.2 g (9.6 mnol) of l-Fp-2-butyne5

ing material.

stirred

to the Fe(CO),

(0.42 g., 1.7 nnnol) in freshly distilled

flate was added to this via syringe.

2 hours.

trans

the

cations.'*"

procedure,

solution

tion showed complete

Finally,

of a trace of acid to the p-xylene

band of the silica gel column

since part of it is converted,

complex 2, which

in the

is isolated from the leading

as a dark yellow oil (252 mg):

IR (CH,Cl,)2970, 2940, 2010, 1960, 1040 cm-l, NMR (COCl,) 6 7.45 (s, lH), 6.95 (d, lH, J = 9 Hz), 6.70 (d,

lH, J = 9 Hz) 4.84 (s, 5H), 2.40 (s, 3H), 2.20 (s, 3H). accounted

for by the following

The formation

sequence:

of 2 may be FP i

Fp

7

H+i

FP

The use of 3-substituted derivatives

at C-4 of the hydroazulene propargyl

or allenyl

unsaturation

which

show these to be mixtures

thus provides

a simple route to

at C-l and a carbonyl

while the use of the more highly

allows for regiocontrol

function

unsaturated

in the introduction

of

ring as well.

of a single regioisomeric

in view of the spectral

complexes

system with a substituent

skeleton,

Fp complexes

in the five membered

The formation markable

Fp(ally1)

of the parent complex

cycloadduct

in all of these reactions

analysis of alkyl substituted of two or more structural

tropyliumiron

isomers

is re-

tricarbonyls,

in rapid equilibriun.6

2100

The predominant

isomers for R=Me, Ph, c-C,Hs

C-6 substituted

isomers

and i-C,H, were found to be the C-2, 4 and

10 and 11.

R

b

= @

+Fe(CO)a R

+Fe(C013

The present

the several between

in equilibrium,

Finally, by exposure 5

results may be accounted

when R=OSiMe,

these

+Fe(C013

-11

-10

latter cation

P-

e

for either

in terms of the presence

or OBBu, or of the preferential but the available

evidence

reaction

does not allow us to distinguish

possibilities. removal

of the Fp group

to 1 M sulfuric

in L

(R=Me) is readily

accomplished,

The replacement

acid (THF, 25', 1 h).

(CH, in place of CO, R=Me) by COOMe or*Br has been reported,'

hydroazulene of course,

ligand from the Fe(CO), well precedented

Further

group with Ce(IV)

in the chemistry

use of these reactions

salts.'

of dieneiron

in sesquiterpene

Science

Foundation,

which

is gratefully

in 95% yield,

of Fp, in an analog of

as has the release

of the

This latter reaction

tricarbonyl

synthesis

Support for this work was derived

Acknowledgment. the National

of only the

of this isomer among

is,

complexes.4

is being pursued.

from a grant (CHE-8117510)

from

acknowledged.

References

1.

N. Genco,

2.

0. F. Hunt, G. C. Farrant,

3.

0. Morten,

All new compounds elemental

4. 5.

S. Raghu, M. Rosenblum, G. T. Rodeheaver,

were characterized

J. Am. Chem. Sot., 98, 848 (1976). J. Organometal.

by IR and NMR spectra

Chez,

38, 349 (1972).

and gave ztisfactory

analysis.

A. J. Pearson,

Act. Chem. Res., 13, 463 (1980).

M. R. Churchill,

J. Wormald,

0. z

Ross, J. E. Thomasson,

A. Wojcicki,

J. Am. Chem.

soc.,=r92, 1795 (1970). 6.

C. P. Lewis, W. Kitching,

A. Eisenstadt,

(1979).

(Received

in USA 10 February

1984)

M. Brookhart,

J. Am. Chem. Sot., l&,

4896