5,6-dehydro[3.3]Paracyclophane: Bridged benzobarrelene formation by intramolecular trapping of a novel aryne

Tetrahedron

Letters

No. 50, pp 4559-4562.

1976.

Pergamon

Press.

Printed

in Great Britain.

5,6-DEHYDRO[3.3]PARACYCLOPHANE: BRIDGED

BENZOBARRELENE

FORMATION

Daniel Department

BY INTRAMOLECULAR

of Chemistry,

University

Los Angeles,

OF A NOVEL ARYNE

lb and J. A. Gladys.2

la

T. Longone

TRAPPING

of California,

California

Los Angeles

90024"

and Department

of Chemistry, Ann Arbor,

(Received

in USA 1 September

The steric extensively

inhibition

studied.'

at 200"

(AG* _* ca

tion.3

No evidence

phanes;

optically

mization phane,

38 kcal/mol)

active

undergoes

phane derivatives

ring rotation

have resisted

groups in each bridge permits which

the two benzene

72 hr in refluxing

facile

rings are mutually

tridecane

cleavage

at the benzylic

been observed

(240").4

occurs posi-

in the [3.3]paracyclowithout

race-

Carboxy[4.3]paracyclo-

33.5 kcal/mol),3

and [4.4]paracyclo-

Hence the accumulation of four methylene

to date.5

attainment

has been

(1, X = COOH) was recovered

at 160" (AG* -* ca

resolution

bridge

has ever

5-carboxy[3.3]paracyclophane after

1976)

4-carbomethoxy[2.2]paracyclophane

via homolytic -

by any pathway

25 October

in the [m.n]paracyclophanes

of chiral

and proceeds

of Michigan

48104

in UK for publication

ring rotation

racemization

of ring rotation

or decomposition

however,

1976; received

of benzenoid

Thermal

University

Michigan

(AG' < 20 kcal/mol)

of a transition

state

in

perpendicular.

240" \/, .x

:R)

(s)

In this communication, encumbered benzene

a reaction

5,6-dehydro[3.3]paracyclophane

rings

accessible

we report

required

upon removal

for ring rotation

which

1) requires

(z), 2) demonstrates

the perpendicular

in the [3.3lparacyclophane

of the two offending

vicinal 4559

hydrogens

the intermediacy

series

of an un-

arrangement

is energetically

and superposition

of a trans-

of

No. 50

4560 annular

attraction

provides details

with an energy

a synthetic

entry

into a novel

at that position

bridged

on the reaction

benzobarrelene

system

coordinate,

(4).

and 3)

The experimental

are as follows:

To 108 mg (a.343 mmol) 824 mg (20 equiv) previously

;-BuO-

of 5-bromo[3.3]paracyclophane

K+.

conversion

and preoarative tion afforded

to a single

white

platelets,

m.n.

mixture

(2)6 in 8 ml t-butylbenzene

was refluxed

of arynes 7y8] and monitored product

thin layer chromatogranhy

of sym-hexahydropyrene

C 92.11,

The reaction

used for the generation

quantitative

sample

minimum

was observed,

(52.5 mg, 66%).

130.5-132,

in an oil bath at 185"

(conditions

gas chromatographically.

which

was isolated

distinct

Clean,

by solvent

Slow chloroform-ethanol

chromatographically

(m.p. 13219 and analyzing

was added

removal

recrystalliza-

from an authentic

for (CH), (talc: C 92.26,

H 7.74;

found:

H 7.82).

I \ fsolated

@

The structural spectrum and other

displaysa

assignment molecular

significant

upon extensive

spectral

ion (base peak) at m/e 234 (C18H18,

fragments

178 (131, and 165 (17). multiplets

4 is based

at 235

The proton

characterization. overall

(18%), 233 (12), 206 (21), 205

magnetic

resonance

(6 1.95, 4H; 2.55, 8H; TMS internal

spectrum

standard)

loss of HBr from 2)

(20), 191 (16), 179 (8),

in CDC13

and a single

The mass

reveals

two aliphatic

sharp absorption

at 6 6.61

No.

4561

50

(6H) which

is split into two singlets

recorded

in C6D6. This is consistent

chemical

shifts

barrelene."

are comparable

The uv spectrum

(E 260), 271

(52D), 262

the expected

absorptions

only with

tcle highly

to those reported resembles

(sh, 730), (CHC13,

6.55,

(6.50, 4H, vinylic;

symmetric

by Zimmerman

cm-'):

the spectrum

structure

lo [imax'

213 (sh, 36,000)1,

is

4, and the relevant

for benzobarrelene

that of benzobarrelene

218 (38,090),

2H, aryl) when

10

and anthra-

cyclohexane,

283 nm

and the ir spectrum

features

3042 w, 3008 m, shp, 2978 s, 2958 m, 1482 m, 1448 w,

1447 w, 1441 m, 1431 w, 1396 w, 1336 w, 1335 w, 1328 w, 1257 w, 1184 w, 1093 w, br, 1012 w, br, 955 w, shp, 897 w, shp, 857 w, 838 w, 708 s, 584 m. Previous

can be obtained is apparently

not long enough

trapping

obtained

photochemically

(u,

diminished

a more sophisticated

This

racemization

adduct

in this aryne

analogous adducts

Such species

to 4, but

can be

have received

of (-)-4-methyl[2.2]paracyclo-

K+ addition

to similarly

Therefore

in which the aryne

a perpendicular ring can rotate

to 3, despite _

generated

the barrier

of an extra methylene

4,5-dehydro[2.2]-

to ring rotation

group to each bridge. ring orientation

through

the twenty-

must be

While 2 is

can be thermally

180" without

reaction

awaits

test.

is made to the donors

Society,

from g-BuO-

dominate.

by the addition

of whether

arising

for support

of The Petroleum

of this research.

Research

We warmly

Fund, administered thank

Professor

by the

Cram for the

of 2 used in these experiments.

REFERENCES 1. (a)

length

Diels-Alder

13

derivatives.

is in sharp contrast

such products

chemical

Acknowledgement

sample

The bridge

transannular

in the photochemical

paracyclophane

the question

Chemical

K+.

of an intramolecular

is possible.8

lack of products

where

the smallest-bridged

.heriCan

formation

from [2.2]paracyclophane

of base employed.

substantially

and t-BuO-

that 4,5-dehydro[2.21paracyclophane

compounds.14

paracycloohane,8'12

achieved,

anthracene)

is a complete

fold excess

to allow

as intermediates

phane and related There

demonstrated

from 4-bromoC2.2lparacyclophane

external

consideration

12

work by one of us8 and by Cram

University summer

of Michigan

and Visiting

AND NOTES

Professor

at University

of California,

1976.

(b)

Universit.y of California,

(c)

Contribution

Number

Los Angeles

3688

2.

For a review,

3.

H. J. Reich and 0. J. Cram,

see D. J. Cram and J. M. Cram, Accts.

Chem.

J. Am. Chem. Sot., 91, 3517 _-

Res., 4, 204

(1969).

(1971).

Los Angeles,

4562

No. 50

4.

M. Sheehan,

5.

D. J. Cram. W. 3. Wechter,

Ph.D. Dissertation,

Y. Sheehan

7.

J. I. G. Cadogan,

8.

D. T. Longone

9.

E. A. Coulson, acetylene

and D. J. Cram,

ibid.,

and 5. R.Chipman, Sot.,

California,

J. Am. Chem. Sot., 80, 3126

__

1969.

(1958);

89, 3094 (1958).

91 3544 __,

(1969).

and J, T.Sharp,

J. Chem.

J. Chem. Sot., Chem. 1298

Los Angeles,

(1937).

Barrelenes

Sot.,

Commun.,

C, 1860 (1967).

1358

(1969).

are generally

quite

stable

toward

10ss.'Dyl'

10.

H. E. Zimmerman,

11.

H. E. Zimmerman

12.

I-I,J. Cram

R. S. Givens,

and R. M. Pagni,

and D. R. Amick,

ibid.,

and A. C. Day, J. Org. Chem.,

D. J. Cram,

J. Am. Chem.

13.

H. H. Wasserman

14.

Y. H. Delton reactions

ibid.,

J. K. A. Hall,

3. Chem.

of California,

and R. W. Kierstead,

0. J. Cram and R. A. Reeves, 6.

University

_-

and P. M. Keehn,

and D. J. Cram,

in cyclophanes,

Los Angeles,

Sot., 91, 3527

California,

95, 3977

__

(1968).

see also H. J. Reich and

(1969).

94, 2471

see M. H. Delton, 1970.

90, 6096

(1973).

31, 1227 (1966); -1

ibid., 89 __, 2770

ibid.,

J. Am. Chem. Sot.,

(1967).

(1972).

For a listing

Ph.D. Dissertation,

of transannular

University

of California,